Annual meeting of the HS9 subdivision for Erosion, Sedimentation and River Processes.

Meeting of the subdivision HS10 Ecohydrology, wetlands and estuaries. Exchange on the organization of the EGU General Assembly and general activities of the subdivision. Everybody interested is kindly invited.

The MacGyver session focuses on novel sensors made, or data sources unlocked, by scientists. All geoscientists are invited to present:
- new sensor systems, using technologies in novel or unintended ways,
- new data storage or transmission solutions sending data from the field with LoRa, WIFI, GSM, or any other nifty approach,
- started initiatives (e.g., Open-Sensing.org) that facilitate the creation and sharing of novel sensors, data acquisition and transmission systems.

Connected a sensor for iPhone to an Arduino or Raspberri Pi? 3D printed an automated water quality sampler? Or build a Cloud Storage system from Open Source Components? Show it!

New methods in hydrology, plant physiology, seismology, remote sensing, ecology, etc. are all welcome. Bring prototypes and demonstrations to make this the most exciting Poster Only (!) session of the General Assembly.

This session is co-sponsered by MOXXI, the working group on novel observational methods of the IAHS.

Water is our planet’s most vital resource, and the primary agent in some of the biggest hazards facing society and nature. The twin pressures of population growth and a rapidly changing global climate act as multipliers of water’s value and of water-related hazards.

River streamflow is one of the most crucial hydrological variables for ecology, for people and industry, for flood risk management and for understanding long term changes to the hydrological regime. However, despite significant efforts, long-term, spatially dense monitoring networks remain scarce, and even the best monitoring networks can fail to perform when faced with extreme conditions, and lack the precision and spatial coverage to fully represent crucial aspects of the hydrological cycle.

Happily, a number of new technologies and techniques are emerging which show great potential to meet these challenges. In this context, this session focuses on:
1) Innovative methodologies for measuring/modelling/estimating river stream flows;
2) Real-time acquisition of hydrological variables;
3) Remote sensing for hydrological & morphological monitoring;
4) Measuring extreme conditions associated with a changing climate;
5) Measurement of sudden-onset extreme flows associated with catastrophic events;
6) Strategies to quantify and describe hydro-morphological evolution of rivers;
7) New methods to cope with data-scarce environments;
8) Inter-comparison of innovative & classical models and approaches;
9) Evolution and refinement of existing methods;
10) Guidelines and standards for hydro-morphological streamflow monitoring;
11) Quantification of uncertainties;
12) Development of expert networks to advance methods.

Contributions are welcome with an emphasis on innovation, efficiency, operator safety, and meeting the growing challenges associated with the changing climate, and with natural and anthropogenically driven disasters such as dam failures and flash floods.

Additionally, presentations will be welcomed which explore options for greater collaboration in advancing riverflow methods and which link innovative research to operational monitoring.

This session is sponsored by the COST Action CA16219, Harmonisation of UAS techniques for agricultural and natural ecosystems monitoring (HARMONIOUS).

Within the water cycle, physical and chemical interactions between water, air and land shape the Earth’s surface. Human activity also induces major changes to natural systems at a wide range of temporal and spatial scales. Experimental methods have played – and still play – a fundamental role in Hydrology and Hydraulics. Laboratory- and field-based experiments allow physical systems to be analysed under semi-controlled conditions to understand process-form interactions. As such, experimental studies provide an effective platform for investigating physical processes under controlled hydrometeorological or physical conditions, and improve understanding of the Earth systems.

This session aims to provide with a discussion platform to exchange experiences on the design, methodologies and application of physical experiments in hydrology and hydraulics, both in the laboratory and the field. We welcome experimental research contributions across a series of disciplines with a hydrological, hydraulic and geomorphological focus across a wide range of spatiotemporal scales.

We invite contributions directing on (but not restricted to):
- The use of laboratory- and field-based experiments to understand real-world physical systems with a hydrological, geomorphological or hydraulic focus;
- Fundamental science and practical applications of physical and experimental models such as flumes, lysimeters, soil columns, rainfall simulators or scaled physical systems;
- The application of novel and innovative instrumentation, measurement and visualisation techniques;
- Experimental adaptations to well-established monitoring or data analysis techniques;
- Development and application of hybrid or composite (numerical-physical) models to contribute to numerical modelling frameworks;
- The use of experimental methods and models for science communication and as demonstrative teaching tools.

Geophysical and in-situ measurements of the cryosphere offer important baseline datasets, as well as validation for modelling and remote sensing products. In this session we welcome contributions related to a wide spectrum of methods, including, but not limited to radioglaciology, active and passive seismology, acoustic sounding, Global Navigation Satellite System (GNSS) reflectometry or time delay techniques, cosmic ray neutron sensing, remotely operated vehicle (ROV) or drone applications, geoelectrics, nuclear magnetic resonance (NMR) and methods in radiative transfer (i.e. infrared photography, thermal sounding...).

Contributions could be related to field applications, new approaches in geophysical or in-situ survey techniques, or theoretical advances in data analysis processing or inversion. Case studies from all parts of the cryosphere such as snow and firn, alpine glaciers, ice sheets, glacial and periglacial environments, permafrost, or sea ice, are highly welcome. The focus of the session is to compare experiences in the application, processing, analysis and interpretation of different geophysical and in-situ techniques in these highly complex environments.

This year our session will be a virtual PICO session. The session begins with each presenter giving a “quick fire” 2-minute overview of their research, followed by breakout "rooms" - one per presentation, for authors to further discuss their research. We hope the virtual PICO format will provide as much lively discussion as our normal in-person PICO!

++++++++++++++++++++ Invited Speaker ++++++++++++++++++++

Amy R. Macfarlane: Quasi in-situ snow and sea ice interface microstructure measured by micro-computed tomography

Recent advances in image collection, e.g. using uncrewed aerial vehicles (UAVs), and topographic measurements, e.g. using terrestrial or airborne LiDAR, are providing an unprecedented insight into landscape and process characterization in geosciences. In parallel, historical data including terrestrial, aerial, and satellite photos as well as historical digital elevation models (DEMs), can extend high-resolution time series and offer exciting potential to distinguish anthropogenic from natural causes of environmental change and to reconstruct the long-term evolution of the surface from local to landscape scale.

For both historic and contemporary scenarios, the rise of techniques with ‘structure from motion’ (SfM) processing has democratized data access and offers a new measurement paradigm to geoscientists. Photogrammetric and remote sensing data are now available on spatial scales from millimetres to kilometres and over durations of single events to lasting time series (e.g. from sub-second to decadal-duration time-lapse), allowing the evaluation of event magnitude and frequency interrelationships.

The session welcomes contributions from a broad range of geoscience disciplines such as geomorphology, cryosphere, volcanology, hydrology, bio-geosciences, and geology, addressing methodological and applied studies. Our goal is to create a diversified and interdisciplinary session to explore the potential, limitations, and challenges of topographic datasets for the reconstruction and interpretation of past and present 2D and 3D changes in different environments and processes. We further encourage contributions describing workflows that optimize data acquisition and processing to guarantee acceptable accuracies and to automate data application (e.g. geomorphic feature detection and tracking), and field-based experimental studies using novel multi-instrument and multi-scale methodologies. This session invites contributions on the state of the art and the latest developments in i) modern photogrammetric and topographic measurements, ii) remote sensing techniques as well as applications, iii) modelling technologies, and iv) data processing tools, for instance, using machine learning approaches.

Liaising with stakeholders, policy-makers and society is becoming increasingly important for academic research to turn research into impactful action, but also to improve research by allowing society to take part within research processes in terms of co-producing knowledge and policy. In hydrological sciences, this is needed when implementing innovative solutions in areas such as river basin management, water allocation, impact-based hydrological forecasting, flood protection, drought risk management, climate change mitigation, ecohydrology and sustainable environmental solutions, among others.
Contributions focus on:
1. Science-policy interface in hydrology. How science influences policy and policies impact science? How scientists can provide easily digestible pieces of evidence to policy-makers? What are the key gaps in joining science to feasible policy solutions in the water sector? How can we use knowledge to improve policy, and vice-versa? How do we deal with uncertainty, adaptation, path dependencies but also with aspects of power, inequality and vested interests in the co-production of knowledge and policy?
2. Interdisciplinary collaborations. How do we create the interdisciplinary knowledge needed to address the questions faced by decision-makers and societal stakeholders? How have new, interdisciplinary, science questions been generated in response to existing and emerging research problems? How can individual disciplinary perspectives come together in interdisciplinary studies and experiments?
3. Hydrology as practiced within society. Who are the users of our knowledge, how useful is our knowledge for those societal users, how useful are our tools, models and methods? What approaches are available to support a fruitful collaboration between hydrological science and practitioners? And, since scientists are not removed from the things they study, how has hydrological science been shaped by the historical interplay of cultural, political and economic factors? What are the opportunities and challenges that this science/society nexus creates for producing scientific knowledge?

The International Association of Hydrological Sciences (IAHS) coordinates two initiatives in hydrology:

- The Panta Rhei hydrological decade 2013- 2022, focusing on gains in our understanding of water cycle processes, their changing dynamics in respect of interactions and feedbacks with human systems. [1]
- The 23 Unsolved Problems in Hydrology (UPH), launched in 2017 after a public consultation process, in collaboration with the Hydrology Divisions of EGU and AGU as well as the IAH. [2]

This session presents works related to these initiatives.

Approaching the end of this Panta Rhei decade (2013-2022), it is time to synthesize the achievements of this decade. The main focus of this grand synthesis, which will be published in an IAHS book, is on coevolution and prediction of coupled human-water systems, including understanding of emergent phenomena, mechanisms, and implications for predictions and practices. Focus is put on theoretical/conceptual framework for understanding changes in hydrology and society; coevolution and emergent phenomena; dynamic models; data needs and acquisition; benchmark datasets in various context and scales, including human-flood, human-drought, agricultural, transboundary and global systems. Case studies from Panta Rhei working groups, IAHS Commissions and beyond are also welcome.

The 23 UPH are articulated around 7 themes: Time variability and change, Space variability and scaling, Variability of extremes, Interfaces in hydrology, Measurements and data, Modelling methods, and Interfaces with society. A crucial issue is to put together fragmented knowledge to address the questions raised and enhance coherence in hydrological sciences. The purpose of this session is to present research results that advance the understanding of any of the 23 UPH, review (or present a contribution to review) the state of the art of one (or more) of the UPH, pointing towards directions where progress is most promising.

[1] Panta-Rhei: https://iahs.info/Commissions--W-Groups/Working-Groups/Panta-Rhei.do
[2] 23 UPH: https://doi.org/10.1080/02626667.2019.1620507

Understanding the complex interactions of the coupled terrestrial-atmospheric water cycle requires cross-compartment strategies encompassing coupled modeling from the bedrock to the top of the atmosphere, integrated hydro-meteorological observations and datasets, novel data assimilation schemes and multivariable validation approaches. The objective of the session is to create opportunities for interdisciplinary exchange of ideas and experiences among members of the Earth System and hydrology communities. Contributions are invited dealing with the complex interactions between groundwater, surface water, land surface and atmospheric processes with a specific focus on the development, application and validation of novel one-way (both deterministic and ensemble) or fully-coupled hydrometeorological modeling systems for process understanding and predictions and projections across various space- and time scales. This includes also combined dynamical-statistical approaches and studies addressing data assimilation in coupled models. An additional focus is placed on the use of field experiments and testbeds equipped with complex sensors and measurement systems allowing cross-compartment and multivariable validation of these modeling systems.

This session focuses on advances in theoretical, methodological and applied studies in hydrologic and broader earth system dynamics, regimes, transitions and extremes, along with their physical understanding, predictability and uncertainty, across multiple spatiotemporal scales.

The session further encourages discussion on interdisciplinary physical and data-based approaches to system dynamics in hydrology and broader geosciences, ranging from novel advances in stochastic, computational, information-theoretic and dynamical system analysis, to cross-cutting emerging pathways in information physics.

Contributions are gathered from a diverse community in hydrology and the broader geosciences, working with diverse approaches ranging from dynamical modelling to data mining, machine learning and analysis with physical process understanding in mind.

The session further encompasses practical aspects of working with system analytics and information theoretic approaches for model evaluation and uncertainty analysis, causal inference and process networks, hydrological and geophysical automated learning and prediction.

The operational scope ranges from the discussion of mathematical foundations to development and deployment of practical applications to real-world spatially distributed problems.

The methodological scope encompasses both inverse (data-based) information-theoretic and machine learning discovery tools to first-principled (process-based) forward modelling perspectives and their interconnections across the interdisciplinary mathematics and physics of information in the geosciences.

Take part in a thrilling session exploring and discussing promising avenues in system dynamics and information discovery, quantification, modelling and interpretation, where methodological ingenuity and natural process understanding come together to shed light onto fundamental theoretical aspects to build innovative methodologies to tackle real-world challenges facing our planet.

We are glad to welcome Mahesh Maskey (dynamical systems) and Uwe Ehret (information theory) as our invited authors for this eclectic session, where we promote a fruitful cross-fertilisation between complementary visions of the world.

In recent years, the geoscience community has been making strides towards making our science more open, inclusive, and accessible, driven both by individual- or community-led initiatives and by broader-scale regulatory changes. Open-source software, accessible codebases and open online collaboration resources (such as GitHub, VHub, etc.) are becoming the norm in many disciplines. The open-access publishing landscape has been changing too: several geoscience journals have defined data availability policies, and many publishers have introduced green and gold open-access options to their journal collections. Pre-print servers and grassroots diamond open-access journals are changing the readiness with which scholarly content can be accessed beyond the traditional paywall model.

However, good scientific practice requires research results to be reproducible, experiments to be repeatable and methods to be reusable. This can be a challenge in geosciences, with available data sets that are becoming more complex and constantly superseded by new, improved releases. Similarly, new models and computational tools keep emerging in different versions and programming languages, with a large variability in the quality of the documentation. Moreover, how data and models are linked together towards scientific output is very rarely documented in a reproducible way. As a result, very few published results are reproducible for the general reader. These challenges especially apply to hydrology, which is highlighted here as an example in the general geosciences.

This session is designed to gain a community overview of the current open-science landscape and how this is expected to evolve in the future. It aims to foster a debate on open science, lower the bar for engaging in open science and showcase examples, including software and other instruments for assisting open research. This may include software and tools, open science dissemination platforms (such as pre-print servers and journals), the teams driving the development of open-science resources and practices, and discussion on the regulatory moves towards standardising open access in the scientific community and what those policies mean in practice. The session has a focus on hydrological sciences, as an example within the geosciences. This session should advance the discussion on open and reproducible science, highlight its advantages and also provide the means to bring this into practice.

Water is a strategic issue in the Mediterranean region, mainly because of the scarcity of the available resources, in quantity and/or quality. The Mediterranean climate and the surface hydrology are characterized by a strong variability in time and space and the importance of extreme events, droughts and floods. This irregularity is also met at a lower level in aquifers dynamics. During the last century, modifications of all kinds and intensities have affected surface conditions and water uses. The Mediterranean hydrology is then continuously evolving.

This session intends to identify and analyse the changes in the Mediterranean hydrology, in terms of processes, fluxes, location. It will gather specialists in observation and modeling of the various water fluxes and redistribution processes within the catchments.
Contributions addressing the following topics are welcome:

• Spectacular case studies of rapid changes in water resources;
• Using various sources of information for comparing past and present conditions;
• Differentiating climatic and anthropogenic drivers (including GCM reanalysis);
• Modelling hydrological changes (in surface and/or ground water);
• Impacts of extreme events on water systems.

Annually, various parts of Africa are affected by climate related impacts, such as droughts, flooding etc., to varying degrees of severity. Global and regional hydrological models have recently seen tremendous advances in improved representations of physical processes underpinning these impacts, resulting in better reproductions of observed variables such as streamflow and water extent. As a result, they are increasingly used for predicting socio-economic risks of floods, droughts and water stress in regions around the globe. However, the use of hydroclimatic models for disaster risk reductions in data-sparse regions, while gradually improving, is still limited in comparison.
This session aims to bring together communities working on different strands of African hydrology, climate and other water-related topics, including environmental and food security. We welcome both fundamental and applied research in the areas of hydrological process understanding, flood forecasting and mapping, seasonal forecasting, water resources management, climate impact assessment and societal impacts. Interdisciplinary studies aiming at increasing our understanding of the physical drivers of water-related risks and their impacts in Africa are encouraged. Case studies showcasing practical experiments and innovative solutions in decision making under large uncertainty are welcomed.

A large proportion of the global stream network comprises channels that cease to flow or dry periodically. These systems range from near-perennial rivers with infrequent, short periods of zero flow to rivers experiencing flow only episodically following large rainfall events. Intermittent and ephemeral rivers support a unique high-biodiversity because they are coupled aquatic-terrestrial systems that accommodate a wide range of aquatic, semi-aquatic and terrestrial flora and fauna. Extension and connection of the flowing stream network can affect the quantity and quality of water in downstream perennial rivers. In many arid conditions, they are the main source of fresh water for consumptive use. However, in many places intermittent and ephemeral rivers lack protection and adequate management. There is a clear need to study the hydrology, ecology and biogeochemistry of natural intermittent and ephemeral streams to characterize their flow regimes, to understand the main origins of flow intermittence and how this affects their biodiversity, and to assess the consequences of altered flow intermittency (both increased and decreased) in river systems.
This session welcomes all contributions on the science and management of intermittent and ephemeral streams, and particularly those illustrating:
• current advances and approaches in characterizing and modelling flow intermittency,
• the effects of flow in intermittent streams on downstream perennial streams,
• the factors that affect flowing stream network dynamics
• land use and climate change impacts on flow intermittency,
• links between flow intermittency and biogeochemistry and/or ecology.

Agriculture plays a vital role in the socio-economic development. For agricultural production, whether rainfed or using irrigation, water is a key requirement. Therefore, a thorough understanding of the hydrological processes in agricultural lands is essential to address a wide range of issues, including soil moisture condition, crop water requirement, agricultural productivity, water efficiency, soil erosion, and solute transport.
This session is intended to address and advance our understanding of the role of hydrological processes in agricultural lands. Some of the topics and questions of interest are: (1) modelling the impacts of climate change on water balance and agricultural productivity at watershed scale; (2) identification of dominant hydrological factors and how they can be measured locally for improving water supply to crops; (3) effects of irrigation schemes on regional evapotranspiration and soil moisture content; (4) effects of artificial drainage on water regime and solute transport at different spatial scales; (5) aquifer vulnerability to high rates of fertilizer and pesticide applications; (6) multi-process and multi-scale water and energy transitions in agricultural lands; (7) water and energy responses of water-saving practice; and (8) linking hydrological issues with other environmental issues, including removal of natural vegetation, drought or flood events, and soil erosion. We welcome abstracts addressing the above topics or other topics related to hydrological processes in agricultural lands.

Forests are recognized as prime regulators of the hydrological cycle. Their change has effects on the ecosystem services they provide via their water and biochemical cycles. The traditional idea that forest hydrology emphasizes the role of forests and forest management practices on runoff generation and water quality has been broadened in the light of rapid global change. Some of the largest pristine forested areas are in the tropics and have suffered drastic land-use changes during recent decades. These tropical systems are still markedly underrepresented in hydrological studies compared to temperate regions, especially concerning long-term experimental setups and monitoring networks.
Anthropogenic intervention is exerting enormous pressure on natural ecosystems, affecting water quantity and quality, and, consequently, threatening socio-economic and human development as described by the UN Sustainable Development Goals. Yet, we lack a proper understanding of how catchments respond to changing environmental conditions and disturbances. To answer these open questions, it requires interdisciplinary approaches in combination with novel monitoring methods and modelling efforts. This session brings together studies that will enhance our understanding and stimulate discussions on the impact of global change on hydrological processes in forest systems at different scales.
We invite field experimentalists and modelers to submit contributions that investigate hydrological processes in forests from boreal to tropical regions, including water quality, the carbon cycle, or ecohydrological aspects.
This session welcomes studies that:
1) Improves our understanding of forested hydrological processes using an experimental or modelling approach or a combination of both;
2) Assesses the hydrological-related impacts of land use/cover change in forested systems;
3) Presents new methods (e.g. remote sensing techniques) or tools that unveils new perspectives or data sources in forest hydrology;
4) Includes interdisciplinary research that supports the consideration of overlooked soil-plant-atmosphere components in hydrological studies.

Despite only representing about 25% of continental land, mountains are an essential part of the global ecosystem and are recognised to be the source of much of the world’s surfaces water supply apart from important sources of other commodities like energy, minerals, forest, and agricultural products, and recreation areas. In addition, mountains represent a storehouse for biodiversity and ecosystem services. People residing within mountains or in their foothills represent approximately 26% of the world’s population, and this percentage increases to nearly 40% when considering those who live within watersheds of rivers originated in a mountain range. This makes mountains particularly sensitive to climate variability, but also unique areas for identifying and monitoring the effects of global change thanks to the rapid dynamics of their physical and biological systems.
This session aims to bring together the scientific community doing hydrology research on mountain ranges across the globe to share results and experiences. Therefore, this session invites contributions addressing past, present, and future changes in mountain hydrology due to changes in either climate and/or land use, how these changes affect local and downstream territories, and adaptation strategies to ensure the long-term sustainability of mountain ecosystem services, with a special focus on water cycle regulation and water resources generation. Example topics of interest for this session are:
• Sources of information for evaluating past and present conditions (in either surface and/or groundwater systems).
• Methods for differentiating climatic and anthropogenic drivers of hydrological change.
• Modelling approaches to assess hydrological change.
• Evolution, forecasting, and impacts of extreme events.
• Case studies on adaptation to changing water resources availability.

By accumulating precipitation at high elevations, snow and ice change the hydrologic response of a watershed. Water stored in the snow pack and in glaciers thus represents an important component of the hydrological budget in many regions of the world and a sustainment to life during dry seasons. Predicted impacts of climate change in headwater catchments (including a shift from snow to rain, earlier snowmelt and a decrease in peak snow accumulation) will affect both water resources distribution and water uses at multiple scales, with potential implications for energy and food production.
Our knowledge about snow/ice accumulation and melt patterns is highly uncertain, because of both limited availability and inherently large spatial variability of hydrological and weather data in remote areas at high elevations. This translates into limited process understanding, especially in a warming climate. The objective of this session is to integrate specialists focusing on snow accumulation and melt within the context of catchment hydrology and snow as a source for glacier ice and melt, hence streamflow. The aim is to integrate and share knowledge and experiences about experimental research, remote sensing and modelling.
Contributions addressing the following topics are welcome:
- experimental research on snowmelt runoff processes and potential implementation in hydrological models;
- development of novel strategies for snowmelt runoff modelling in various (or changing) climatic and land-cover conditions;
- evaluation of remote-sensing (time-lapse imagery, laser scanners, radar, optical photography, thermal and hyperspectral technologies) or in-situ snow products (albedo, snow cover or depth, snow water equivalent) and application for snowmelt runoff calibration, data assimilation, streamflow forecasting or snow and ice physical properties quantification;
- observational and modelling studies that shed new light on hydrological processes in glacier-covered catchments, e.g., impacts of glacier retreat on water resources and water storage dynamic or the application of techniques for tracing water flow paths;
- studies on cryosphere-influenced mountain hydrology, such as landforms at high elevation and their relationship with streamflow, water balance of snow/ice-dominated, mountain regions.

Snow cover characteristics (e.g. spatial distribution, surface and internal physical properties) are continuously evolving over a wide range of scales due to meteorological conditions, such as precipitation, wind and radiation.
Most processes occurring in the snow cover depend on the vertical and horizontal distribution of its physical properties, which are primarily controlled by the microstructure of snow (e.g. density, specific surface area). In turn, snow metamorphism changes the microstructure, leading to feedback loops that affect the snow cover on coarser scales. This can have far-reaching implications for a wide range of applications, including snow hydrology, weather forecasting, climate modelling, and avalanche hazard forecasting or remote sensing of snow. The characterization of snow thus demands synergetic investigations of the hierarchy of processes across the scales ranging from explicit microstructure-based studies to sub-grid parameterizations for unresolved processes in large-scale phenomena (e.g. albedo, drifting snow).

This session is therefore devoted to modelling and measuring snow processes across scales. The aim is to gather researchers from various disciplines to share their expertise on snow processes in seasonal and perennial snowpacks. We invite contributions ranging from “small” scales, as encountered in microstructure studies, over “intermediate” scales typically relevant for 1D snowpack models, up to “coarse” scales, that typically emerge for spatially distributed modelling over mountainous or polar snow- and ice-covered terrain. Specifically, we welcome contributions reporting results from field, laboratory and numerical studies of the physical and chemical evolution of snowpacks, statistical or dynamic downscaling methods of atmospheric driving data, assimilation of in-situ and remotely sensed observations, representation of sub-grid processes in coarse-scale models, and evaluation of model performance and associated uncertainties.

Understanding and representing hydrological processes is the basis for developing and improving hydrological and Earth system models. Modeling and learning is a symbiotic and continuous process through which our understanding of human-natural systems is formulated and tested constantly. As a result, a variety of models are developed and trained by quantitative and qualitative data across desired temporal and spatial scales.
In this session, we welcome contributions on the development of novel data sets and frameworks for model development and evaluation across spatio-temporal scales from catchment to continental scale hydrology. The vision of our session, following the initiative of 23 Unsolved Problems in Hydrology (UPH, https://doi.org/10.1080/02626667.2019.1620507), is to address three questions: What are the hydrologic laws at the catchment scale and how do they change with scale? How can hydrological models be adapted to be able to extrapolate to changing conditions, including changing vegetation dynamics? How can we disentangle and reduce model structural/parameter/input uncertainty in hydrological prediction?

We welcome contributions that (but not limited to):
(1) introduce new global and regional data products into the modeling process;
(2) introduce new approaches for model calibration and evaluation, especially to improve process representation, and/or to improve model predictions under changing conditions;
(3) improve model structure by representing often neglected processes in hydrological models such as human impacts, river regulations, irrigation, as well as vegetation dynamics;
(4) provide novel concepts for improving the characterization of internal and external model fluxes and their spatio-temporal dynamics;
(5) upscale experimentalists' knowledge from smaller to larger scale by identifying driving forces for spatial patterns for a better usage of them in models;
(6) suggest more effective monitoring and seamless modeling of spatial patterns in hydrology and land models using distributed earth observations;
(7) develop novel approaches and performance metrics for evaluating and constraining models in space and time; and
(8) identify model limitations and conceptual improvements that are of general relevance to the geosciences modeling community.

This session is organized as part of the grass-root modelling initiative on "Improving the Theoretical Underpinnings of Hydrologic Models" launched in 2016.

Stable and radioactive isotopes as well as other natural and artificial tracers are useful tools to fingerprint the source of water and solutes in catchments, to trace their flow pathways or to quantify exchanges of water, solutes and particulates between hydrological compartments. Papers are invited that demonstrate the application and recent developments of isotope and other tracer techniques in field studies or modelling in the areas of surface / groundwater interactions, unsaturated and saturated zone, rainfall-runoff processes, nutrient or contaminant export, ecohydrology or other catchment processes.

Salinisation of both groundwater and surface water resources is a growing problem, threatening freshwater security for agricultural, domestic and industrial purposes, as well as biodiversity, in many regions of the world. Although the problem of freshwater salinisation is increasingly recognised, there are major research gaps in terms of its impacts, extent and magnitude, particularly at cross-regional to global scales. Both observational, remote sensing and model-driven approaches are needed to improve our understanding of salinisation processes, drivers and impacts across different scales, and to ensure sustainable water resources management today and in the future.

This session aims to bring together scientists working on salinity monitoring (in-situ or remote sensing) data, as well as model-driven studies related to quantifying and predicting historic to future salinisation patterns, drivers and impacts at catchment to global scales. Contributions including - but not limited to - any of the following topics are of particular interest for this session:

- Surface water and groundwater interactions and its effects on salinity dynamics
- Impacts of hydrological extremes and seasonality on salinity levels of freshwater resources
- Human and hydro-climatic drivers of freshwater salinisation across different spatial and temporal scales
- Implications of inland salinity for ecosystem health and sectoral water use
- Applications of surface and/or groundwater in-situ and remote sensing data, and/or data-driven models to determine salinity concentrations across multiple scales
- Global change (e.g. climate change, land use change) impacts on future freshwater salinisation
- Assessment of management and adaptation measures to salinity changes

Land use and climate change as well as legal requirements (e.g. the EU Water Framework Directive) pose challenges for the assessment and sustainable management of surface water quality at the catchment scale. Sources and pathways of nutrients and other pollutants as well as nutrient interactions have to be characterized to understand and manage the impacts in river systems. Additionally, water quality assessment needs to cover the chemical and ecological status to link the hydrological view to aquatic ecology.
Models can help to optimize monitoring schemes and provide assessments of future change and management options. However, insufficient temporal and/or spatial resolution, a short duration of observations and the widespread use of different analytical methods restrict the data base for model application. Moreover, model-based water quality calculations are affected by errors in input data, model errors, inappropriate model complexity and insufficient process knowledge or implementation. Additionally, models should be capable of representing changing land use and climate conditions, which is a prerequisite to meet the increasing needs for decision making. The strong need for advances in water quality models remains.

This session aims to bring scientist together who work on experimental as well as on modelling studies to improve the prediction and management of water quality constituents (nutrients, organic matter, algae, or sediment) at the catchment scale. Contributions are welcome that cover the following issues:

- Experimental and modelling studies on the identification of sources, hot spots, pathways and interactions of nutrients and other, related pollutants at the catchment scale
- New approaches to develop efficient water quality monitoring schemes
- Innovative monitoring strategies that support both process investigation and model performance
- Advanced modelling tools integrating catchment as well as in-stream processes
- Observational and modelling studies at catchment scale that relate and quantify water quality changes to changes in land use and climate
- Measurements and modelling of abiotic and biotic interaction and feedback involved in the transport and fate of nutrients and other pollutants at the catchment scale
- Catchment management: pollution reduction measures, stakeholder involvement, scenario analysis for catchment management

Surface water quality is typically assessed and managed at the catchment scale. Management decisions needs a sound process knowledge and understanding of underlying cause-effect relationships to be effective. However, the dynamics of solute and particulate concentrations integrate a multitude of hydrological and biogeochemical processes interacting at different temporal and spatial scales, which are difficult to assess using local field experiments. Hence, time series of water quality observed at the outlet of catchments can be highly beneficial to understand these processes. Long-term, high-frequency as well as multiple-site datasets can be used to inform experimental and modelling studies and formulate hypotheses on dominant ecohydrological and geochemical processes moving “from pattern to process”. Recent advances in this field have used concentration-discharge relationships to infer the interplay between hydrological and biogeochemical controls, both in the terrestrial part of catchments and in the river network. Long-term time series of nutrient input-output relationships help understand nutrients legacy effects and catchments response times. High-frequency observations allow understanding the fine structure of concentration dynamics, including flowpaths and their age distribution during runoff events and ecological controls on diel cycles. When multiple catchments are monitored, it is possible to relate water quality metrics to catchment properties to conclude on dominant processes.
This session aims to bring together studies using data-driven analysis of river concentration time series to infer solute and particulate mobilization, retention and export mechanisms. We strongly encourage studies that use findings from data-driven analysis to build conceptual and process-based models. Presentations of the following topics are invited:
- Interpretation of C-Q relationships from storm events to long-term shifts
- Utilization of high-frequency observations of water quality
- Long-term changes of nutrient inputs, outputs and nutrient stoichiometry
- Role of hydrological extremes such as the recent mid-European droughts in long-term trajectories of nutrient exports
- Instream, network and lake effects on nutrient load and concentration dynamics
- Utilizing time series of compound-specific isotopic fingerprints
- Linkage of water travel time distribution and water quality dynamics

A large number of pathogens, micropollutants and their transformation products (veterinary and human pharmaceuticals, personal care products, pesticides and biocides, chlorinated compounds, heavy metals) pose a risk for soil, groundwater and surface water. The large diversity of compounds and of their sources makes the quantification of their occurrence in the terrestrial and aquatic environment across space and time a challenging task. Regulatory monitoring programmes cover a small selection out of the compound diversity and quantify these selected compounds only at coarse temporal and spatial resolution. Carefully designed monitoring however allows to detect and elucidate processes and to estimate parameters in the aquatic environment. Modeling is a complementary tool to generalize measured data and extrapolate in time and space, which is needed as a basis for scenario analysis and decision making.

This session invites contributions that improve our quantitative understanding of the sources and pathways, mass fluxes, the fate and transport of micropollutants and pathogens in the soil-groundwater-river continuum. Topics cover:
- Novel sampling and monitoring concepts and devices
- New analytical methods, new detection methods for DNA, pathogens, micropollutants, non-target screening
- Experimental studies and modelling approaches to quantify diffuse and point source inputs
- Novel monitoring approaches such as non-target screening as tools for improving processes understanding and source identification such as industries
- Comparative fate studies on parent compounds and transformation products
- Diffuse sources and (re-)emerging chemicals
- Biogeochemical interactions and impact on micropollutant behaviour

Plastic pollution in freshwater systems is a widely recognized global problem with potential environmental risks to water and sediment quality. Furthermore, freshwater plastic pollution is also considered the dominant source of plastic input to the oceans. Despite this, research on plastic pollution has only recently expanded from the marine environment to freshwater systems. Therefore data and knowledge from field studies are still limited in regard to freshwater environments. Sources, quantities, distribution across environmental matrices and ecosystem compartments, and transport mechanisms remain mostly unknown at catchment scale. These knowledge gaps must be addressed to understand the dispersal and eventual fate of plastics in the environment, enabling a better assessment of potential risks as well as development of effective mitigation measures.
In this session, we explore the current state of knowledge and activities on macro-, micro- and nanoplastics in freshwater systems, including aspects such as:
• Plastics in rivers, lakes, urban water systems, floodplains, estuaries, freshwater biota;
• Monitoring and analysis techniques;
• Source to sink investigations, considering quantities and distribution across environmental matrices (water and sediment) and compartments (water surface layer, water column, ice, riverbed, and riverbanks);
• Transport processes of plastics at catchment scale;
• The role of river regulation structures, e.g. dams, navigation, flood control, etc., in plastic retention and transport
• Effects of hydrological extremes, e.g. accumulation of plastics during droughts, and short-term export during floods in the catchment;
• Degradation and fragmentation processes, e.g. from macro- to micro- and nanoplastics;
• Modelling approaches for local and/or global river output estimations;
• Legislative/regulatory efforts, such as monitoring programs and measures against plastic pollution in freshwater systems.

(Contributions with a strong focus on remote sensing of plastics are encouraged to be submitted to the session “Detecting and Monitoring Plastic Pollution in Rivers, Lakes, and Oceans”)

This session presents the works submitted to session HS2.3.5 “Fate and transport processes of pathogens and emerging contaminants at multiple scales” and to session HS6.9 “From short-term detection to long-term projections: complementing water quality assessments by combining modelling and remote sensing”.
HS2.3.5 Invited speaker: Dr. Liping Pang, ESR Christchurch, NZ
The occurrence of pathogens and an exponentially increasing number of contaminants in freshwater and estuary environments pose a serious problem to public health. There is a need to better understand the dominant processes controlling fecal indicator, pathogen and contaminant fate and transport at larger scales. Consequently, we welcome contributions that include both small and large-scale experimental and modelling studies with a focus on:
- The development of novel experimental and analytical methods to investigate fate and transport of fecal indicators, pathogens and emerging contaminants in rivers, groundwater and estuaries
- Hydrological, physically based modelling approaches
- Methods for identifying the dominant processes and for transferring fecal indicator, pathogen and contaminant transport parameters from the laboratory to the field or catchment scale
- Investigations of the implications of contamination of water resources for water safety management planning and risk assessment frameworks

HS6.9
Climate change and major socio-economic developments such as increasing population and expanding public water supplies that fail to adequately treat wastewater flows lead to significant water quality deterioration. An exponentially increasing number of contaminants and nutrients in freshwater and estuary environments pose a serious problem to public and ecosystem health. This part of the session focuses on regional and global water quality research where remote sensing and modelling are combined in order to complement a water quality assessment compared to one based on monitoring data only. Topics of interest:

- Remote sensing facilitating water quality model development and modelling
- Processing water quality data from remote sensing products across scales
- Improve water quality assessments

Our invited speaker is Lucy Marshall from the University of New South Wales, Sydney, Australia.

The application of multi-datasets and multi-objective functions has proven to improve the performance of hydrologic and water quality models by extracting complementary information from multiple data sources or multiple features of modelled variables. This is useful if more than one variable (runoff and snow cover, sediment or pollutant concentration) or more than one characteristic of the same variable (e.g., flood peaks and recession curves) are of interest.
Similarly, a multi-model approach can overcome shortcomings of individual models, while testing a model at multiple scales helps to improve our understanding of the model functioning in relation to catchment processes. Finally, the quantification of multiple uncertainty sources enables the identification of their individual contributions and this is critical for uncertainty reduction and decision making under uncertainty. In this aspect, Bayesian approaches emerge as very powerful tools for comprehensive handling of uncertainty in data, model structure and parameters.

This session welcomes contributions that apply one or more of the multi-aspects in hydrologic and water quality studies. In particular, we seek studies covering the following issues:
• Frameworks using multi-objectives or multi-variables to improve the identification (prediction) of hydrologic or water quality models
• Studies using multi-model or multiple-data-driven approaches
• Use of multiple scales or sites to improve understanding of catchment processes
• Assimilation of remote sensed data or use of multi-datasets to improve model identification
• Hypothesis testing with one of the multi-aspects
• Metaheuristics (e.g., Monte Carlo) or Bayesian approaches in combination with multi-aspects of model identification
• Techniques to optimize model calibration or uncertainty quantification via multi-aspect analyses
• Studies handling multiple uncertainty sources in a modelling framework
• Bayesian applications to address the problem of scaling (e.g. disparity between process, observations, model resolution and predictions) through hierarchical models
• Bayesian approaches to model water quality in data sparse environments
• Applications of Bayesian Belief Networks as decision support tools
• Application of machine learning and data mining approaches to learn from large, multiple or high-resolution data sets.

Estimates of water availability and flooding risks remain one of the central scientific and societal challenges of the 21st century. The complexity of this challenge arises particularly from transient boundary conditions: Increasing atmospheric greenhouse gas concentrations lead to global warming and an intensification of the water cycle and finally to shifts in the temporal and spatial distribution of precipitation and terrestrial water availability. Likewise, large-scale land use changes impact and alter regional atmospheric circulation, thereby local precipitation characteristics and again terrestrial water availability. Also the feedbacks between the interlinked terrestrial and atmospheric processes on different spatial and temporal scales are still poorly understood.
This session therefore invites contributions addressing past, present and prospective changes in regional hydrological behaviour due to either (or joint) climate- and/or land use changes. We especially welcome contributions on the development of novel methods and methodologies to quantify hydrological change. Further aspects of this topic comprise particularly:

- Robustness of hydrological impact assessments based on scenarios using downscaled climate model – hydrology model modelling chains.
- Quantification of regional land use change predictions and impact of past, present and future land use changes on water and energy fluxes in meso- to large-scale catchments.
- Joint or coupled modelling of water and energy fluxes between the atmosphere and the land surface/subsurface and analyses of feedback mechanisms.
- Climate change/land use change signal separation techniques and quantification of future land use change vs. climate change induced hydrological change.
- Adequate handling of climate change and land use change data and their uncertainty for the forcing of hydrological models.
- Case studies of regional hydrological behaviour in climate sensitive and flood or drought prone regions worldwide.

In the current context of global change, assessing the impact of climate variability and changes on hydrological systems and water resources is increasingly crucial for society to better-adapt to future shifts in water resources as well as extreme conditions (floods and droughts). However, hitherto, important sources of uncertainties have often been neglected in projecting climate impacts on hydrological systems, especially uncertainties associated with internal/natural climate variability, whose contribution to near-future changes could be as important as forced anthropogenic climate changes at the regional scales. Internal climate modes of variability (e.g. ENSO, NAO, AMO) and their impact on the continent are not always properly reproduced in the current global climate models, leading to large underestimations of decadal climate and hydroclimatic variability at the global scale. At the same time, hydrological response strongly depends on catchment properties, whose interactions with climate variability are little understood at the decadal timescales. These factors altogether reduce significantly our ability to understand long-term hydrological variability and to improve projection and reconstruction of future and past hydrological changes on which improvement of adaption scenarios depends.

We welcome abstracts capturing recent insights for understanding past or future impacts of large-scale climate variability on hydrological systems and water resources as well as newly developed projection and reconstruction scenarios. Results from model intercomparison studies are encouraged.

Hydrological extremes (floods and droughts) have major impacts on society and ecosystems and are expected to increase in frequency and severity with climate change. Although both at the extreme ends of the hydrological spectrum, floods and droughts are governed by different processes, which means that they operate on different spatial and temporal scales and that different approaches and indices are needed to characterise them. However, there are also many similarities and links between the two extremes that are increasingly being studied.

This session on hydrological extremes aims to bring together the two communities in order to learn from the similarities and differences between flood and drought research. We aim to increase the understanding of the governing processes of both hydrological extremes, find robust ways of modelling and analysing floods and droughts, assess the influence of global change on hydroclimatic extremes, and study the socio-economic and environmental impacts of both extremes.

We welcome submissions that present innovative flood and/or drought research, including insightful case studies, large-sample studies, statistical hydrology, and analysis of flood or drought nonstationarity under the effects of climate change, land cover change, and other anthropogenic influences.

This session is jointly organised by the Panta Rhei Working Groups “Understanding Flood Changes”, “Changes in Flood Risk”, and “Drought in the Anthropocene” and will further stimulate scientific discussion on change detection, attribution, and the feedbacks between hydrological extremes and society. The session is linked to the European Low Flow and Drought Group of UNESCO´s IHP-VIII FRIEND-Water Program, which aims to promote international drought research. Submissions from early-career researchers are especially encouraged.

Key topics:
Floods, Droughts, or both
Hydrological extremes
Large-sample hydrology or insightful case studies
Flood and drought nonstationarity
New approaches for analysis of extremes
Spatial and temporal variability

The space-time dynamics of floods are controlled by atmospheric, catchment, river system and anthropogenic processes and their interactions. The natural oscillatory behaviour of floods (between flood-rich and flood-poor periods) superimpose with anthropogenic climate change and human interventions in river morphology and land uses. In addition, flood risk is further shaped by continuous changes in exposure and vulnerability. Despite more frequent exploratory analyses of the changes in spatio-temporal dynamics of flood hazard and risk, it remains unclear how and why these changes are occurring. The scope of this session is to report when, where, how (detection) and why (attribution) changes in the space-time dynamics of floods occur. Of particular interest is what drivers are responsible for observed changes. Presentations on the impact of climate variability and change, land use changes and morphologic changes in streams, as well as on the role of pre-flood catchment conditions in shaping flood hazard and risk are welcome. Furthermore, contributions on the impact of socio-economic and structural factors on past and future risk changes are invited. This session is jointly organised by the Panta Rhei Working Groups “Understanding Flood Changes” and “Changes in Flood Risk”. The session will further stimulate scientific discussion on flood change detection and attribution. Specifically, the following topics are of interest for this session:
- Decadal oscillations in rainfall and floods
- Process-informed extreme value statistics
- Interactions between spatial rainfall and catchment conditions shaping flood patterns
- Detection and attribution of flood hazard changes: atmospheric drivers, land use controls and river training, among others
- Changes in flood risk: urbanisation of flood prone areas; implementation of risk mitigation measures, such as natural water retention measures; changes of economic, societal and technological drivers; flood damages; flood vulnerability; among others.
- Future flood risk changes and adaptation and mitigation strategies

Flash droughts (FDs) are distinguished from slower-developing droughts by their rapid rate of intensification. They may occur during the initial stage of a long-term drought, represent a period of rapid intensification within a longer-term drought, or terminate after a relatively short, yet impactful, event. Due to their rapid development, FDs are difficult to manage and can be particularly devastating for agriculture. They can occur with little or no warning due to limitations in monitoring capabilities, prediction skill of relevant environmental variables, and understanding of key physical mechanisms. Efforts to create working definitions of FD have been hindered by these limitations and a lack of data to quantify the many impacts associated with FD. This session welcomes abstracts relating to:
1) proposed FD definitions,
2) regionality and seasonality of FD physical mechanisms,
3) advances in FD detection and monitoring,
4) predictability and prediction of FDs,
5) quantification of impacts of FD, and
6) the changes in FD frequency and intensity in response to human-induced climate change.
We also encourage contributions that benefit from multivariate analysis, model-observation comparison, uncertainty quantification, or machine-learning predictions.

With global climate change affecting the frequency and severity of extreme meteorological and hydrological events, it is particularly necessary to develop models and methodologies for a better understanding and forecasting of present day weather induced hazards. Future changes in the event characteristics as well as changes in vulnerability and exposure are among the further factors for determining risks for infrastructure and society, and for the development of suitable adaptation measures. This session considers extreme events that lead to disastrous hazards induced by severe weather and climate change. These can, e.g., be tropical or extratropical rain- and wind-storms, hail, tornadoes or lightning events, but also floods, long-lasting periods of drought, periods of extremely high or of extremely low temperatures, etc. Papers are sought which contribute to the understanding of their occurrence (conditions and meteorological development), to assessment of their risk and their future changes, to the ability of models to reproduce them and methods to forecast them or produce early warnings, to proactive planning focusing to damage prevention and damage reduction. Papers are also encouraged that look at complex extreme events produced by combinations or sequences of factors that are not extreme by themselves. The session serves as a forum for the interdisciplinary exchange of research approaches and results, involving meteorology, hydrology, hazard management and applications like insurance issues.

Global, continental, and other large-scale hydrological research is very important in many different contexts. Examples include; increasing understanding of the climate system and water cycle, assessment of water resources in a changing environment, hydrological forecasting, and water resource management.

We invite contributions from across the atmospheric, meteorological and hydrological communities. In particular, we welcome abstracts that address advances in:

(i) understanding and predicting the current and future state of our global and large scale water resources;

(ii) use of global earth observations and in-situ datasets for large scale hydrology and data assimilation techniques for large scale hydrological models;

(iii) understanding and modelling of extremes: like droughts and floods.

(iv) representing and evaluating different components of the terrestrial water cycle fluxes and storages (e.g. soil moisture, snow, groundwater, lakes, floodplains, evaporation, river discharge) and their impact on current and future water resources and atmospheric modelling.

(v) synthesis studies assembling knowledge gained from smaller scales (e.g. catchments or hillslope) to advance our knowledge on process understanding needed for the further development of large scale models and to identify large scale patterns and trends.

Since early work on the assessment of global, continental and regional-scale water balance components, many studies use different approaches including global models, as well as data-driven approaches that ingest in-situ or remotely sensed observations or combination of these. They attempted to quantify water fluxes (e.g. evapotranspiration, runoff/discharge, groundwater recharge) and water storages on the terrestrial part of the Earth, either as total estimates (e.g. from GRACE satellites) or in separate compartments (e.g. water bodies, snow, soil, groundwater). In addition, more and more attention is given to uncertainties that stem from forcing datasets, model structure, parameters and combinations of these. Current estimates in literature show that flux and storage calculations differ considerably due to the methodology and datasets used such that a robust assessment of global, continental and regional water balance components is challenging.
This session is seeking for contributions that are focusing on the:
i. past/future assessment of water balance components (fluxes and storages) such as precipitation, river discharge to the oceans (and/or inland sinks), evapotranspiration, groundwater recharge, water use, changes in terrestrial water storage or individual components at global, continental and regional scales,
ii. application of innovative explorative approaches undertaking such assessments – through better use of advanced data driven, statistical approaches and approaches to assimilate (or accommodate) remote sensing datasets for improved estimation of terrestrial water storages/fluxes,
iii. analysis of different sources of uncertainties in estimated water balance components,
iv. examination and attribution of systematic differences in storages/flux estimates between different methodologies, and/or
v. applications/consequences of those findings such as sea level rise and water scarcity.
We encourage submissions using different methodological approaches. Contributions could focus on any of the water balance components or in an integrative manner with focus on global, continental or regional scale applications. Assessments of uncertainty in past/future estimates of water balance components and their implications are highly welcome.

Large-sample studies lead to generalizable insights about hydrologic similarity, understanding of dominant hydrologic processes and modelling capabilities. Studies that investigate the organization and response of single catchments (e.g. well-monitored experimental catchments, innovative process models) can provide a testing ground for hydrologic theories that can scaled up to larger samples. Combining detailed local knowledge with large data samples can provide insights unavailable to either approach alone, about e.g. hydrologic organization across large spatial scales or across varied hydroclimatic conditions.

This session provides the opportunity for researchers to highlight recent data and model-based efforts on catchment organization, diversity and response. We specifically encourage studies that seek to advance understanding of the following topics:

1. Data mobilization for hydrologic similarity and regionalization:
Can currently available global datasets of hydrologically relevant information (e.g. soil properties, land use, soil moisture estimates, meteorological re-analysis) effectively be used to define hydrologic similarity and thus improve the prediction in ungauged or scarcely gauged basins?

2. Testing of hydrologic theories:
To what extent can hydrologic theory developed in well-monitored experimental catchments be transferred to larger samples of relatively data-scarce catchments?

3. Modelling capabilities:
What can large sample hydrology reveal about the strengths and weaknesses of current modelling capabilities and how can large sample approaches be used to improve and constrain modelling efforts?

4. Explaining water use dynamics:
How can we use large sample hydrology to better understand water resource use, allocation and future availability, and inform sustainable management of these resources?

5. Development and improvement of large-sample data sets:
How can we overcome current challenges on unequal geographical representation of catchments, quantification of uncertainty, catchment heterogeneity and inclusion of human interaction with the global water cycle?

A splinter meeting is planned to discuss development and improvement of large-sample data sets, titled “Large sample hydrology: facilitating the production and exchange of data sets worldwide”. See the final program for location and timing.

The session and splinter meeting are organized as part of the Panta Rhei Working Group on large-sample hydrology.

Reducing natural hazard risk is high on the global political agenda. In response, more and more risk datasets, methods, and models are being developed and applied together with stakeholders in the decision-making process. At the same time, climate change, globalisation, urbanisation, and increased interconnectedness between ecological, physical, human, and technological systems pose major challenges to disaster risk reduction in a globally interconnected world. COVID-19 has clearly shown that single-hazard approaches to disaster risk management can leave countries unprepared. This calls for novel scientific approaches and new types of data, including loss data, to integrate the study of multiple natural and human processes. The integration of socioeconomic loss databases in risk assessments allows for effective use for both science and policy. This session is a merger between the following sessions:

Global and continental scale risk assessment for natural hazards: methods, practice and open loss and risk assessment
In this sub-session we: (1) showcase current state-of-the-art in global and continental natural hazard risk science, assessment, and application; (2) foster exchange of knowledge and good practice between scientists and practitioners; and (3) collaboratively identify future research avenues. We examine all aspects of natural hazard risk assessment at the continental to global scale, including contributions focusing on single hazards, multiple hazards, or a combination or cascade of hazards. It includes contributions focusing on globally applicable methods, such as using globally available datasets to force more local models or inform more local risk assessment.

Interplay between natural hazards and vulnerable societies in the context of global change
This sub-session aims to: (1) gather research, empirical studies, and observation data that are useful for understanding and assessing risk to inform resilience building strategies in the context of global change, (2) identify persistent gaps, and (3) propose potential ways forward. The session welcomes contributions on the following topics, among others: What can we learn from comparative studies of past successes and failures? Why do we still see increasing impacts of natural hazards despite major progress in understanding their drivers and constant innovation in methods? Which approaches are needed to assess and manage multi-hazard and multi-risk?

Hydroinformatics has emerged over the last decades to become a recognised and established field of independent research within the hydrological sciences. Hydroinformatics is concerned with data acquisition, development and hydrological application of mathematical modelling, information technology, systems science and computational intelligence tools. We also have to face the challenges of the so-called Big Data: large data sets, both in size and complexity. Methods and technologies for data handling, visualization and knowledge acquisition are often referred to as Data Science.

The aim of this session is to provide an active forum in which to demonstrate and discuss the integration and appropriate application of emergent computational technologies in a hydrological modelling context. Topics of interest are expected to cover a broad spectrum of theoretical and practical activities that would be of interest to hydro-scientists and water-engineers. We aim to address the following classes of methods and technologies:

* Predictive and analytical models based on the methods of statistics, computational intelligence, machine learning : neural networks (including deep learning), fuzzy systems, genetic programming, cellular automata, chaos theory, etc.
* Innovative sensing techniques: satellites, gauges and citizens (crowdsourcing)
* Methods for the analysis of complex data sets, including remote sensing data: principal and independent component analysis, time series analysis, information theory, etc.
* Specific concepts and methods of Big Data and Data Science
* Optimisation methods associated with heuristic search procedures: various types of evolutionary algorithms, randomised and adaptive search, etc.
* Applications of systems analysis and optimisation in water resources
* Hybrid modelling involving different types of models both process-based and data-driven, combination of models (multi-models), etc.
* Data assimilation and model reduction in integrated modelling
* Novel methods of analysing model uncertainty and sensitivity
* Software architectures for linking different types of models and data sources

Applications could belong to any area of hydrology or water resources: rainfall-runoff modelling, flow forecasting, sedimentation modelling, analysis of meteorological and hydrologic data sets, linkages between numerical weather prediction and hydrologic models, model calibration, model uncertainty, optimisation of water resources, etc.

Geostatistical methods are commonly applied in the Water, Earth and Environmental sciences to quantify spatial variation, produce interpolated maps with quantified uncertainty and optimize spatial sampling designs. Space-time geostatistics explores the dynamic aspects of environmental processes and characterise the dynamic variation in terms of correlations. Geostatistics can also be combined with machine learning and mechanistic models to improve the modelling of real-world processes and patterns. Such methods are used to model soil properties, produce climate model outputs, simulate hydrological processes, and to better understand and predict uncertainties overall. Big data analysis and data fusion have become major topics of research due to technological advances and the abundance of new data sources from remote and proximal sensing as well as a multitude of environmental sensor networks. Methodological advances, such as hierarchical Bayesian modeling, machine learning, sparse Gaussian processes, local interaction models, as well as advances in geostatistical software modules in R and Python have enhanced the geostatistical toolbox.

This session aims to provide a forum where scientists from different disciplines can present and discuss innovative geostatistical methods targeting important problems in the Water, Earth and Environmental sciences. We also encourage contributions focusing on real-world applications of state-of-the-art geostatistical methods.

The topics of interest include:
1) Space-time geostatistics for hydrology, soil, climate system observations and modelling
2) Hybrid methods: Integration of geostatistics with optimization and machine learning approaches
3) Advanced parametric and non-parametric spatial estimation and prediction techniques
4) Big spatial data: analysis and visualization
5) Optimisation of spatial sampling frameworks and space-time monitoring designs
6) Algorithms and applications on Earth Observation Systems
7) Data Fusion, mining and information analysis
8) Geostatistical characterization of uncertainties and error propagation
9) Bayesian geostatistical analysis and hierarchical modelling
10) Functional data analysis approaches to geostatistics
11) Multiple point geostatistics

This session is co-sponsored by the International Association for Mathematical Geosciences (IAMG), https://www.iamg.org/

Machine learning (ML) is now widely used across Hydrology and the broader Earth Sciences and especially its subfield deep learning (DL) has recently enjoyed increased attention.. This session highlights the continued integration of ML, and its many variants, including deep learning (DL), into traditional and emerging Hydrology-related workflows. Abstracts are solicited related to novel theory development, novel methodology, or practical applications of ML and DL in hydrological modeling. This might include, but is not limited to, the following:

(1) Development of novel DL models or modeling workflows.
(2) Integrating DL with process-based models and/or physical understanding.
(3) Improving understanding of the (internal) states/representations of ML/DL models.
(4) Understanding the reliability of ML/DL, including under nonstationarity.
(5) Deriving scaling relationships or process-related insights with ML/DL.
(6) Modeling human behavior and impacts on the hydrological cycle.
(7) Hazard analysis, detection, and mitigation.
(8) Natural Language Processing in support of models and/or modeling workflows

Clustering analysis is a well-known exploratory task for partitioning databases into smaller groups based on patterns or inherent similarity in data. Clustering methods have found many applications in many disciplines due to growing interest in unravelling the hidden and meaningful patterns that exist in large amounts of available data. Due to its unsupervised nature, clustering data is a complex task that requires attention to optimal choice alternatives regarding methods, model parameters and performance metrics. However, the suitability of clustering algorithms depends on their application. Different methods and approaches co-exist in a large pool. The challenge is to obtain application-specific insights while enabling a practical knowledge perspective for benchmarking. There are still research gaps in the wider clustering literature, and hydrology-specific knowledge is fragmented and difficult to find.

In hydrology, unsupervised classification of multivariate data is often used but typically in rather basic forms and as an intermediate step. Recently, the number of studies using clustering methods has rapidly increased. However, a clear and integrative vision on clustering algorithms is currently missing. Despite advances in other fields, the scope of hydrological studies is limited. Knowledge exchange on hydrology-specific ways of dealing with the issues related to clustering is needed.

The aim of this session is to explore theoretical and conceptual underpinnings of well-known clustering methods, offer fresh insights into applications of new clustering methods, gain thorough understanding of pearls and pitfalls in clustering algorithms, provide a critical overview of the main challenges associated with data clustering process, discuss major research trends and highlight open research issues. It is expected to improve scientific practice within the hydrology domain, and foster scientific debate on benchmarking in cluster analysis.

We invite contributions (case studies, comparative analyses, theoretical experiments) on a wide range of topics including (but not limited to): hard vs fuzzy clustering; comparison of clustering algorithms; benchmarking in cluster analysis; clustering as an exploratory tool vs clustering as a hypothesis testing tool; determination of number of clusters; selecting variables to cluster upon; evaluation of clustering performance; alternative clustering methods (sequential, evolutionary, deep, ensemble, etc.)

Proper characterization of uncertainty remains a major challenge and is inherent to many aspects of modelling such as structural development, hypothesis testing and parameter estimation, and the adequate characterization of parameters, forcing data and initial and boundary conditions. To address this challenge, useful methods are uncertainty analysis, sensitivity analysis and inversion (calibration), either in Bayesian, geostatistical or conventional manners.

This session invites contributions that discuss advances, both in theory and/or application, in methods for SA/UA and inversion applicable to all Earth and Environmental Systems Models (EESMs). This includes all areas of hydrology, such as classical hydrology, subsurface hydrology and soil science.

Topics of interest include (but are not limited to):
1) Novel methods for effective characterization of sensitivity and uncertainty,
2) Novel approaches for parameter estimation, data inversion and data assimilation,
3) Novel methods for spatial and temporal evaluation/analysis of models,
4) Single- versus multi-criteria SA/UA/inversion,
5) The role of data information and error on SA/UA (e.g., input/output error, model structure error, worth of data etc.), and
6) Improving the computational efficiency of SA/UA/inversion (efficient sampling, surrogate modelling, parallel computing, model pre-emption, etc.).

Contributions addressing any or all aspects of sensitivity/uncertainty, including those related to structural development, hypothesis testing, parameter estimation, data assimilation, forcing data, and initial and boundary conditions are invited. We also invite instances of the above research questions applied to scientifically built machine-learning models.

This interdisciplinary session welcomes contributions on novel conceptual and/or methodological approaches and methods for the analysis and statistical-dynamical modeling of observational as well as model time series from all geoscientific disciplines.
Methods to be discussed include, but are not limited to linear and nonlinear methods of time series analysis. time-frequency methods, statistical inference for nonlinear time series, including empirical inference of causal linkages from multivariate data, nonlinear statistical decomposition and related techniques for multivariate and spatio-temporal data, nonlinear correlation analysis and synchronisation, surrogate data techniques, filtering approaches and nonlinear methods of noise reduction, artificial intelligence and machine learning based analysis and prediction for univariate and multivariate time series.
Contributions on methodological developments and applications to problems across all geoscientific disciplines are equally encouraged. We particularly aim at fostering a transfer of new methodological data analysis and modeling concepts among different fields of the geosciences.

___

Sub-Session "Mathematical Climatology and Space-time Data Analysis" (Abdel Hannachi, Amro Elfeki, Christian Franzke, Muhammad Latif, Carlos Pires)

The recent progress in mathematical methods to solve various problems in weather & climate nonlinear dynamics and data analysis calls for the need to develop a new session that focus on those methods. Novel and powerful mathematical methods have been developed and used in different subjects of climate. Because those methods are used within specific contexts they go unnoticed most of the time by climate researchers. The proposed new session will provide the opportunity to climate scientists and researchers working on developing mathematical methods for climate to come together and present their findings in a transparent way. This will also be easily accessible to other climate scientists who look for, and are interested in specific methods to solve their problems.
Contributions are encouraged from researchers working on mathematical methods and their application to weather and climate. We particularly welcome contributions on optimization, dimension reduction and data mining, space-time patterns identification, machine learning, statistical prediction modelling, nonlinear methods , Bayesian statistics, and Monte-Carlo Markov Chain (MCMC) methods in stochastic modelling.

Heavy precipitation events in small and medium size catchments can trigger flash floods, which are characterized by very short response times and high specific peak discharges, and often occur in ungauged basins. Under appropriate geomorphological conditions, such rainstorms also cause debris flows or shallow landslides mobilizing large amounts of unconsolidated material. Although significant progress has been made in the management of these different hazards and related risks, they remain poorly understood and their predictability is affected by large uncertainties, due to the fast evolution of triggering rainfall events, the lack of appropriate observations, the high variabilities and non-linearities in the physical processes, and the high variability and complexity of societal vulnerability.
This session aims to illustrate current advances in monitoring, understanding, modelling, and forecasting flash floods and associated geomorphic processes, and documenting and anticipating the societal impacts and social responses.
Contributions on the following scientific themes are more specifically expected:
- Development of new measurement techniques adapted to flash floods and/or rainfall-induced geomorphic hazards monitoring (including in-situ sensors and remote sensing data, such as weather radar, and lightning ..), and quantification of the associated uncertainties,
- Identification of processes leading to flash flood events and/or rainfall-induced geomorphic hazards from data analysis and/or modelling, and of their characteristic space-time scales,
- Possible evolutions in hazard characteristics and frequency related to climate change,
- Development of short-range (0-6h) rainfall forecasting techniques adapted to heavy precipitation events, and representation of associated uncertainties,
- Development of hydro-meteorological forecasting chains for predicting flash floods and/or rainfall-induced geomorphic hazards in gauged and ungauged basins,
- Development of inundation mapping approaches specifically designed for an integration in flash floods monitoring or forecasting chains,
- Use of new criteria such as specific “hydrological signatures” (high water marks, impacts and damages, ..) or other proxy data for model and forecast evaluation,
- Observation, understanding and prediction of the societal vulnerability and social responses to flash floods and/or associated hydro-geomorphic hazards.

Drought and water scarcity are important issues in many regions of the Earth. While an increase in the severity and frequency of droughts can lead to water scarcity situations, particularly in regions that are already water-stressed, overexploitation of available water resources can exacerbate the consequences of droughts. In the worst case, this can lead to long-term environmental and socio-economic impacts. It is, therefore, necessary to improve both monitoring and sub-seasonal to seasonal forecasting for droughts and water availability and to develop innovative indicators and methodologies that translate the information provided into effective drought early warning and risk management. This session addresses statistical, remote sensing and physically-based techniques, aimed at monitoring, modelling and forecasting hydro-meteorological variables relevant to drought and/or water scarcity. These include, but are not limited to, precipitation, snow cover, soil moisture, streamflow, groundwater levels, and extreme temperatures. The development and implementation of drought indicators meaningful to decision-making processes, and ways of presenting and explaining them to water managers, policymakers and other stakeholders, are further issues that are addressed. The session aims to bring together scientists, practitioners and stakeholders in the fields of hydrology and meteorology, as well as in the field of water resources and/or risk management; interested in monitoring, modelling and forecasting drought and water scarcity, and in analyzing their interrelationships, hydrological impacts, and the feedbacks with society. Particularly welcome are applications and real-world case studies in regions subject to significant water stress, where the importance of drought warning, supported through state-of-the-art monitoring and forecasting of water resources availability is likely to become more important in the future. Contributors to the session are invited to submit papers to the Special Issue (SI) entitled "Recent advances in drought and water scarcity monitoring, modelling, and forecasting", to be published in the open-access journal Natural Hazard and Earth System Sciences (https://www.natural-hazards-and-earth-system-sciences.net/special_issues/schedule.html). Submission is open until 31 December 2020, for manuscripts that are not under consideration for publication elsewhere.

This session brings together scientists, forecasters, practitioners and stakeholders interested in exploring the use of ensemble hydro-meteorological forecast techniques in hydrological applications: e.g., flood control and warning, reservoir operation for hydropower and water supply, transportation, and agricultural management. It will address the understanding of sources of predictability and quantification and reduction of predictive uncertainty of hydrological extremes in deterministic and ensemble hydrological forecasting. Uncertainty estimation in operational forecasting systems is becoming a more common practice. However, a significant research challenge and central interest of this session is to understand the sources of predictability and development of approaches, methods and techniques to enhance predictability (e.g. accuracy, reliability etc.) and quantify and reduce predictive uncertainty in general. Ensemble data assimilation, NWP preprocessing, multi-model approaches or hydrological postprocessing can provide important ways of improving the quality (e.g. accuracy, reliability) and increasing the value (e.g. impact, usability) of deterministic and ensemble hydrological forecasts. The models involved with the methods for predictive uncertainty, data assimilation, post-processing and decision-making may include machine learning models, ANNs, catchment models, runoff routing models, groundwater models, coupled meteorological-hydrological models as well as combinations (multimodel) of these. Demonstrations of the sources of predictability and subsequent quantification and reduction in predictive uncertainty at different scales through improved representation of model process (physics, parameterization, numerical solution, data support and calibration) and error, forcing and initial state are of special interest to the session.

The session welcomes new experiments and practical applications showing successful experiences, as well as problems and failures encountered in the use of uncertain forecasts and ensemble hydro-meteorological forecasting systems. Case studies dealing with different users, temporal and spatial scales, forecast ranges, hydrological and climatic regimes are welcome.

The session is part of the HEPEX international initiative: www.hepex.org

This interactive session aims to bridge the gap between science and practice in operational forecasting for different water-related natural hazards. Operational (early) warning systems are the result of progress and innovations in the science of forecasting. New opportunities have risen in physically based modelling, coupling meteorological and hydrological forecasts, ensemble forecasting, impact-based forecasting and real time control. Often, the sharing of knowledge and experience about developments are limited to the particular field (e.g. flood forecasting or landslide warnings) for which the operational system is used.
The focus of this session will be on bringing the expertise from different fields together as well as exploring differences, similarities, problems and solutions between forecasting systems for varying natural hazards. Real-world case studies of system implementations - configured at local, regional and national scales - will be presented, including trans-boundary issues. An operational warning system can include, for example, monitoring of data, analysing data, making forecasts, giving warning signals and suggesting response measures.
Contributions are welcome from both scientists and practitioners who are involved in developing operational forecasting and/or management systems for water-related natural or man-made hazards, such as flood, drought, tsunami, landslide, hurricane, hydropower, pollution etc.

The Sendai Framework for disaster risk reduction (SFDRR) and its seventh global target recognizes that increased efforts are required to develop risk-informed and impact-based multi-hazard early warning systems. Despite significant advances in disaster forecasting and warning technology, it remains challenging to produce useful forecasts and warnings that are understood and used to trigger early actions. Overcoming these challenges requires understanding of the reliability of forecast tools and implementation barriers in combination with the development of new risk-informed processes. It also requires a commitment to create and share risk and impact data and to co-produce impact-based forecasting models and services. To deal with the problem of coming into action in response to imperfect forecasts, novel science-based concepts have recently emerged. As an example, Forecast-based Financing and Impact-based Multi-Hazard Early Warning Systems are currently being implemented operationally by both governmental and non-governmental organisations in several countries as a result of increasing international effort by several organizations such as the WMO, World Bank, IFRC and UNDRR to reduce disaster losses and ensuring reaching the objectives of SFDRR. This session aims to showcase lessons learnt and best practices on impact-based multi-hazards early warning system from the perspective of both the knowledge producers and users. It presents novel methods to translate forecast of various climate-related and geohazards into an impact-based forecast. The session addresses the role of humanitarian agencies, scientists and communities at risk in creating standard operating procedures for economically feasible actions and reflects on the influence of forecast uncertainty across different time scales in decision-making. Moreover, it provides an overview of state-of-the-art methods, such as using Artificial Intelligence, big data and space applications, and presents innovative ways of addressing the difficulties in implementing forecast-based actions. We invite submissions on the development and use of operational impact-based forecast systems for early action; developing cost-efficient portfolios of early actions for climate/geo-related impact preparedness such as cash-transfer for droughts, weather-based insurance for floods; assessments on the types and costs of possible forecast-based disaster risk management actions; practical applications of impact forecasts.

Hydrological forecasting can benefit from a better understanding of urban floods and of the thresholds values of the hydrological variables that are crucial for making decisions. This session addresses these two aspects.
Urban flooding is becoming a major issue in many megacities around the world due to a lack of adequate storm water management, hydrologic design, and failure of aging hydrologic infrastructure. To model such extreme flood events, it is of utmost importance to develop state-of-the-art disaster mitigation and damage reduction measures, as well as one and two-dimensional hydrologic and coupled hydrodynamic modelling approaches. Innovative methods are needed to address the modelling and management of urban floods and their spatial and temporal complexity. The session discusses urban floods analysis and measures to mitigate the effects of these events, emerging (e.g., Internet-of-Things (IoT)-based) flood monitoring systems, street-level flood forecasting, dissemination of flood warnings and measures to evacuate people, case studies that provide a better understanding of urban flood management, and innovative methods of floodwater conservation, including strategies and practices to control surface runoff at its sources in a sustainable way.
In hydrological forecasting, where the stochastic nature of the processes makes impossible a deterministic forecast of both the magnitude of the processes and their effects, threshold values can be of great importance and usefulness. Thresholds can be simple (e.g., the threshold of rainfall intensity that might separate stratiform from convective rainfall) or complex and multi-variate (e.g., the threshold for damaging snow-melt flooding, or the threshold for intense hillslope erosion in an agricultural field). They can be useful for real-time forecasts based on simple thresholds on rainfall data (e.g., activation of mass movements such as landslides, debris flow, rill and inter-rill erosion, etc.), for the adoption of satellite data in the management of ground actions (e.g., values of the satellite indexes to be used in irrigation management), for distinguishing among water flow regimes, among other applications.

Statistical post-processing techniques for weather, climate, and hydrological forecasts are powerful approaches to compensate for effects of errors in model structure or initial conditions, and to calibrate inaccurately dispersed ensembles. These techniques are now an integral part of many forecasting suites and are used in many end-user applications such as wind energy production or flood warning systems. Many of these techniques are flourishing in the statistical, meteorological, climatological, hydrological, and engineering communities. The methods range in complexity from simple bias correction up to very sophisticated distribution-adjusting techniques that take into account correlations among the prognostic variables.

At the same time, a lot of efforts are put in combining multiple forecasting sources in order to get reliable and seamless forecasts on time ranges from minutes to weeks. Such blending techniques are currently developed in many meteorological centers.

In this session, we invite presentations dealing with both theoretical developments in statistical post-processing and evaluation of their performances in different practical applications oriented toward environmental predictions, and new developments dealing with the problem of combining or blending different types of forecasts in order to improve reliability from very short to long time scales.

Sociohydrology aims to better understand the dynamic interactions and feedbacks in human-water systems as well as their implications for the assessment and management of water resources and hydrological risks. While acknowledging that the human impact on natural processes has reached unprecedented levels, the sociohydrological perspective provides for a comprehensive understanding of integrated water systems and aims to identify adequate solutions for water supply, management, and adaptation to risk.

Sociohydrology offers novel entry points for a more fertile engagement between hydrological and social sciences across different scales ranging from the plot level to entire watersheds. Its interdisciplinary nature encompasses (and integrates) various methodological approaches, epistemologies, and disciplines.

We welcome contributions from researchers from social and natural sciences who are keen to look beyond their research perspective and who like to discuss their research findings in a broader context of coupled human water systems, i.e. the subject matter of socio-hydrology. Abstracts are solicited on topics that deal with planetary water boundary concepts, integrated assessment models (IAMs), water history and archaeology, sustainability of engineered river basins, water valuation (both monetary and non-monetary), urbanizing deltas etc. with a focus on understanding feedbacks and the spatial and temporal dynamics between human society (from individuals to global levels) and their environment and/or simulating plausible co-evolutionary dynamics that emerges into the future. Resulting policy insights for a sustainable future are equally welcomed. Coupled systems can be human-flood systems, human-infrastructure systems, human-irrigation systems, human-agricultural systems, human-delta systems etc.

Papers should 1) contribute to the understanding of complex human-water relations and their management, 2) discuss the benefits and shortcomings based on empirical, conceptual or model-based research and disciplinary perspective; and 3) shed light on the added value of socio-hydrological modelling for risk-based decision making and adaptation design. This session is jointly developed with the framework of the Panta Rhei Research Initiative of the International Association of Hydrological Sciences (IAHS).

Land use and land cover (LULC) changes are known to be one of the main drivers of the alteration of hydrological processes, impacting water resources availability and other Nature’s Contribution to Peoples (NCPs) via the many functions of water that are intricately linked to complex ecosystem dynamics. LULC changes can be determined by anthropic and/or natural drivers and may affect a large array of hydrological processes including rainfall interception, evapotranspiration, moisture recycling, runoff generation, erosion, groundwater recharge, pollution and alteration of surface and groundwater quality. Their analysis is therefore key to inform adequate water resources management.

The session therefore welcomes studies exploring different aspects of the water-land nexus, including, but not limited to:
• Advances in the quantification of hydrological impacts of LULC changes through modelling and experimental data, including water quantity and quality
• Disentanglement of LULC and climate change impacts on hydrological processes and water resources
• The impact and extent of large scale land and water acquisitions (grabbing)
• Impacts of deforestation and reforestation, with a focus on tropical areas
• Spatial assessments of Water-related Ecosystem Services (WES) - Nature’s Contribution to Peoples (NCPs)

Many water sectors are already coping with extreme weather events, climate variability and change. Such stressors, together with the dynamic interconnection between water and other critical infrastructures, are creating a wealth of challenges and opportunities for improving water resources forecasting and management. By providing science-based and user-specific information on potential impacts of variations in water availability at multiple timescales, operational hydro-meteorological and climate services are invaluable to a range of water-related sectors. Providing skilful forecasts is just one part of the equation; effectively informing operational decisions with this newly available information is necessary to the design and implementation of adaptive and robust water management solutions. Yet, this comes with the additional challenge of accounting for existing operational complexity, including multi-sectoral water demands or electricity prices.

This session brings together HS4.6 - “From sub-seasonal forecasting to climate projections: predicting water availability and servicing water sectors” and HS5.2.1 - “Water resources policy and management - forecast and control methods”. In this merged session, we propose a forum for discussing novel contributions related to the research and operational advances in climate and hydro-meteorological forecasting and services, improved multi-sectoral forecasts on multiple timescales (e.g., water availability and demand, energy and crop prices), novel data analytics and machine learning tools for processing observational data, real-time control solutions taking advantage of this new information, and real-world examples on the successful application of these methods into decision-making practice.

Climate change, world population forecasts of 9 billion by 2050, growing urbanisation and irrigated agriculture will add extra pressures on water resources and the environment. Groundwater is worldwide the main source for domestic supply and irrigation. Water scarcity occurs facing a severe combination of a lack and increasing demand for high-quality water. As a result, a negative water balance is widespread established. Pressures on groundwater arise from pollution sources mainly due to the agriculture use of chemicals as well as to the inflows of domestic and industrial wastewater into aquifers. Approximately 70% of the population on earth lives in coastal areas and most of these people depend on coastal aquifers for freshwater, facing salinization problems. Many islands face seawater intrusion problems. Many coastal aquifer systems are reported to be affected by quality and quantity deteriorations due to seawater intrusion and irrational management. In this framework, the challenge is reconciling demand satisfaction, durable quality and quality sustainability of resources, and climate change, pursuing adaptation and mitigation solutions.

This session accepts the challenge calling any contribution to previous subjects which include any useful innovative scientific activities. A non-exhaustive list of desired contributions includes tools, equipment, methods, modelling, and/or experiences on hydrogeological, geophysical, geochemical mapping and aquifer characterization, including assessment of climate change impacts on groundwater resources in terms of groundwater resource quantity and quality and/or dependent ecosystem status; tools for efficient online visualization and dissemination; risk and vulnerability assessment methods; and monitoring experiences especially if linked to management approaches. All these types of experiences must share the aim of contributing to success in the challenge.

While water plays a critical role in sustaining human health, food security, energy production and ecosystem services, factors such as population growth, climate and land use change increasingly threaten water quality and quantity. The complexity of water resources systems requires methods integrating technical, economic, environmental, legal, and social issues within a framework that allows for the design and testing of efficient and sustainable water management strategies to meet the pressing global water challenges of the 21st century. Current systems analysis practice adopt a practical, problem-oriented approach for addressing the most challenging water issues of our times. It is marked by competing objectives, interdisciplinary processes, and dynamic adaptation under high levels of uncertainty. The session will feature state-of-the-art contributions on systems approaches and solutions for water management in an uncertain environment.

Water sustains societies, economies and ecosystem services globally. Increasing water demands from population growth, coupled with shifts in water availability due to climate and land use change, are increasing competition and conflict over access to and use of freshwater resources in many regions. To address these challenges, integrative approaches to water management and policy are required to balance and manage trade-offs between social, economic and environmental uses of water. This session will provide a forum for showcasing novel and emerging research at the intersection of agricultural production, energy security, economic development, and environmental conservation. In particular, we encourage contributions to the session that: (i) identify knowledge gaps and improvements to understanding about the critical interconnections, feedbacks, and risks between system components, (ii) highlight development of new methods or tools for evaluating and monitoring trade-offs and performance in water allocation and management between different users and sectors, (iii) evaluate alternative technical, policy, and/or governance solutions to address water-food-energy-environment system challenges in different locations and at various scales (local, regional, and even global), and (iv) discuss examples of more and less successful initiatives within research and policy designed to facilitate integrative planning of water-food-energy-environment systems.

The transition to a low-carbon economy will require the development of innovative methods to integrate renewable sources of energy while minimizing the additional pressure on closely connected ecosystems.

Hydropower is a mature and cost-competitive renewable energy source, which helps stabilize fluctuations between energy demand and supply. The structural and operational differences between hydropower systems and renewable energy farms may require changes in the way hydropower facilities operate to provide balancing, reserves or energy storage. Yet, non-power constraints on the hydropower system, such as water supply, flood control, conservation, recreation, navigation may affect the ability of hydropower to adjust and support the integration of renewables. Holistic approaches that may span a range of spatial and temporal scales are needed to evaluate hydropower opportunities and support a successful integration of renewables maintaining a resilient and reliable power grid. In particular, there is a need to better understand and predict spatio-temporal dynamics between climate, hydrology, and power systems.

This session solicits academics and practitioners contributions on novel technical tools and analytics that explore the use of hydropower and storage technologies to support the integration of distributed renewable energy sources in planning and management of low-carbon electricity systems. We specifically encourage interdisciplinary teams of hydrologists, meteorologists, power system engineers, and economists to present on case studies and power grid modernization initiatives, and discuss collaboration with environmental and energy policymakers.

Questions of interest include:
- How to predict water availability and storage capabilities for hydropower production?
- How to predict and quantify the space-time dependences and the positive/negative feedbacks between wind/solar energies, water cycle and hydropower?
- How do energy, land use and water supply interact during transitions?
- What policy requirements or climate strategies are needed to manage and mitigate risks in the transition?
- Quantification of energy production impacts on ecosystems such as hydropeaking effects on natural flow regimes.

This session has the support of the European Energy Research Alliance (EERA) that established the joint program “Hydropower” to facilitate research, promote hydropower and enable sustainable electricity production.

The world's energy, water, and land systems are in transition and rapidly integrating, driven by forces such as socioeconomic, demographic, climatic, and technological changes as well as policies intended to meet Sustainable Development Goals (SDGs) and other societal priorities. These dynamics weave across spatial scales, connecting global markets and trends to regional and sub-regional economies. At the same time, resources are often locally managed under varying administrative jurisdictions closely tied to inherent characteristics of each commodity such as river basins for water, grid regions for electricity and land-use boundaries for agriculture. Local decisions, in turn, are critical in deciding the aggregate success and consequences of national and global policies. Thus, there is a growing need to better characterise the energy-water-land nexus to guide robust and consistent decision making across these scales under changing climate.

This session aims to address this challenge for the energy-water-land nexus in nascent infrastructure planning and sectoral transitions. Contributions can include work dealing with applications of existing nexus approaches in sustainability assessment and design of future developments at different scales (i.e. urban to regional planning), as well as new methods that address existing gaps related to incorporating processes at different scales, bridging data gaps, improving optimisation approaches, or dealing with transboundary issues.

For example, the concepts of water footprint (WF) and water productivity (WP) are widely used in agricultural and industrial production. As a global resource, a wise management of water is not a national matter, it needs to be understood in a global context. To achieve SDGs, water management can be improved through smart consumption and trade of blue and green water resources in all water-related sectors across different scales (local to national to global) to sustain and enhance food and energy supply and manufacturing. Contributions that integratively apply WF and WP concepts in different sectors or scales to study scarcity, sustainability, security, and equity of limited water resources are also welcome.

Water utilities and municipalities must embrace technological innovation to address the exacerbating challenges and uncertainties posed by climate change, urbanization, and population growth. The progressive digitalization of urban water infrastructure and the adoption of IoT solutions for water resources are opening new opportunities for the design, planning, and management of more sustainable and resilient urban water networks and systems. At the same time, the “digital water” revolution is strengthening the interconnection between urban water systems and other critical infrastructure sectors (e.g., energy grids, transportation networks) motivating the development of novel approaches accounting for the intrinsic complexity of such coupled systems. This session aims to provide an active forum to discuss and exchange knowledge on state-of-the-art and emerging tools, framework, and methodologies for planning and management of modern urban water infrastructure, with a focus on digitalization and/or interconnection with other systems. Topics and applications could belong to any area of urban water demand and supply network analysis, modelling and management, including intelligent sensors and advanced metering, digital twins, novel applications of IoT for urban water, and challenges to their implementation or risk of lock-in of rigid system designs. Additional topics may include big-data analytics and information retrieval, data-driven behavioural analysis, descriptive and predictive models of water demand, experimental approaches to demand management, water demand and supply optimization, trend and anomaly (e.g., leak) identification. Examples of interesting investigations on interconnected systems include cyber-physical security of urban water systems (i.e., communication infrastructure), combined reliability studies on power-to-water networks (energy), and minimization of impacts of flooding on urban networks.

Urban areas are at risk from multiple hazards, including urban flooding, droughts and water shortages, sea level rise, disease spread and issues with food security. Consequently, many urban areas are adapting their approach to hazard management and are applying Green Infrastructure (GI) solutions as part of wider integrated schemes.

This session aims to provide researchers with a platform to present and discuss the application, knowledge gaps and future research directions of urban GI and how sustainable green solutions can contribute towards an integrated and sustainable urban hazard management approach. We welcome original research contributions across a series of disciplines with a hydrological, climatic, soil sciences, ecological and geomorphological focus, and encourage the submission of abstracts which demonstrate the use of GI at a wide range of scales and geographical distributions. We invite contributions focusing on (but not restricted to):

· Monitored case studies of GI, Sustainable Drainage Systems (SuDS) or Nature Based Solutions (NBS), which provide an evidence base for integration within a wider hazard management system;
· GIS and hazard mapping analyses to determine benefits, shortcomings and best management practices of urban GI implementation;
· Laboratory-, field- or GIS-based studies which examine the effectiveness or cost/benefit ratio of GI solutions in relation to their wider ecosystem potential;
· Methods for enhancing, optimising and maximising GI system potential;
· Innovative and integrated approaches or systems for issues including (but not limited to): bioretention/stormwater management; pollution control; carbon capture and storage; slope stability; urban heat exchange, and; urban food supply;
· Catchment-based approaches or city-scale studies demonstrating the opportunities of GI at multiple spatial scales;
· Rethinking urban design and sustainable and resilient recovery following crisis onset;
· Engagement and science communication of GI systems to enhance community resilience.

Evapotranspiration (ET), the key component of water and energy balances, has myriad challenges to measure it precisely. In the last two decades, innovative approaches for remote sensing (RS) based measurements of ET has allowed for its measurement in a range of climates on most continents for different green covers. Remotely-sensed ET methods have been proved to be reliable, affordable and applicable to a broad range of scales from plot/field to regional to global in different landscapes including agricultural, forested, riparian zones and urban green spaces.

We invite researchers to contribute abstracts to share their advances and challenges in the development, application, validation, calibration and accuracy assessment of landscape ET through remote sensing platforms. We welcome studies that estimate ET using both prognostic and diagnostic approaches from process-based models that rely on the integration of gridded precipitation and soil-vegetation dynamics to a more direct estimation of ET using remote sensing-based data streams. The scope of the session will include: (1) advances in remote sensing-based ET estimation, (2) applications for a range of land covers and spatiotemporal scales, and (3) accuracy enhancement.

We invite presentations concerning soil moisture estimation, including remote sensing, field experiments, land surface modelling and data assimilation. The technique of microwave remote sensing has made much progress toward its high potential to retrieve surface soil moisture at different scales. From local to landscape scales, several field or aircraft experiments (e.g. SMAPvex) have been organised to improve our understanding of active and passive microwave soil moisture sensing, including the effects of soil roughness, vegetation, spatial heterogeneities, and topography. At continental scales, a series of several passive and active microwave space sensors, including SMMR (1978-1987), AMSR (2002-), ERS/SCAT (1992-2000) provided information on surface soil moisture. Current investigations in L-band passive microwave with SMOS (2009-) and SMAP (2015-), and in active microwave with Metop/Ascat series (2006-) and Sentinel-1, enable accurate quantification of the soil moisture at regional and global scales. Future missions, such as the CIMR Copernicus High Priority Candidate Mission, the EPS-SG Metop-SG/SCA and continuity of the Sentinel programme, will further enhance soil moisture remote sensing accuracy and spatial resolution, and they will ensure continuity of multi-scale soil moisture measurements on climate scales.

We encourage submissions related to soil moisture remote sensing, including:
- Field experiment, theoretical advances in microwave modelling and calibration/validation activities.
- High spatial resolution soil moisture estimation based on e.g. Sentinel observations, GNSS reflections, or using novel downscaling methods.
- Preparation of future missions including CIMR, Metop-SG/SCA, SMOS-High Resolution, Terrestrial Water Resources Satellite, etc.
- Root zone soil moisture retrieval and soil moisture data assimilation in land surface models, hydrological models and in Numerical Weather Prediction models.
- Evaluation and trend analysis of soil moisture climate data records such as the ESA CCI soil moisture product as well as soil moisture from re-analysis (e.g. MERRA2, ERA5, ERA5-Land).
- Inter-comparison and inter-validation between land surface models, remote sensing approaches and in-situ validation networks.
- Application of satellite soil moisture products for improving hydrological applications such as flood prediction, drought monitoring, rainfall estimation.

Snow constitutes a freshwater resource for over a billion of people world-wide. High percentage of this snow mainly come from seasonal snow located in mid-latitude regions. The current warming situation alerts that these snow water storages are in high risk to be dramatically reduced, affecting not only water supply but also ecosystems in these areas. Remote sensing has been the main technique used to monitor the snow properties across mid-large extensions for decades. The recent advances are focused on the study of snow dynamics at higher spatio-temporal scales (i.e., small-scale snow-topography interactions, diurnal variation of snow).

This session will focus on remote sensing studies dealing with techniques and data from different technologies, such as time-lapse imagery, laser scanners, radar, optical photography, thermal and hyperspectral technologies, or other new applications, with the aim of quantifying and better understanding snow characteristics (i.e., snow grain size, snow depth, albedo, pollution load, snow specific area and snow density), snow related processes (snowfall, melting, evaporation and sublimation), snow dynamics, snow hydrological impacts and snow environmental effects.

Remote sensing techniques are widely used to monitor the relationship between the water cycle and vegetation dynamics and its impact on the carbon and energy cycles. Measurements of vegetation water content, transpiration and water stress contribute to a better global understanding of the water movement in the soil-plant system. This is critical for the detection and monitoring of droughts and their impact on biomass, productivity and feedback on water, carbon and energy cycles. With the number of applications and (planned) missions increasing, this session aims to bring researchers together to discuss the current state and novel findings in the remote observation of the interactions between vegetation and hydrology. We aim to (1) discuss novel research and findings, (2) exchange views on what should be done to push the field forward, and (3) identify current major challenges.

We encourage authors to submit presentations on:
• Remote sensing data analyses,
• Modelling studies,
• New hypothesis,
• Enlightening opinions.

The socio-economic impacts associated with floods are increasing. According to the International Disaster Database (EM-DAT), floods represent the most frequent and most impacting, in terms of the number of people affected, among the weather-related disasters: nearly 0.8 billion people were affected by inundations in the last decade (2006–2015), while the overall economic damage is estimated to be more than $300 billion. Despite this evidence, and the awareness of the environmental role of rivers and their inundation, our knowledge and accurate prediction of flood dynamics remain poor, mainly related to the lack of measurements and ancillary data at the global level.

In this context, remote sensing represents a value source of data and observations that may alleviate the decline in field surveys and gauging stations, especially in remote areas and developing countries. The implementation of remotely-sensed variables (such as digital elevation model, river width, flood extent, water level, land cover, etc.) in hydraulic modelling promises to considerably improve our process understanding and prediction. During the last decades, an increasing amount of research has been undertaken to better exploit the potential of current and future satellite observations, from both government-funded and commercial missions. In particular, in recent years, the scientific community has shown how remotely sensed variables have the potential to play a key role in the calibration and validation of hydraulic models, as well as provide a breakthrough in real-time flood monitoring applications. With the proliferation of open data and more Earth observation data than ever before, this progress is expected to increase.

We encourage presentations related to flood monitoring and mapping through remotely sensed data including:

- Remote sensing data for flood hazard and risk mapping, including commercial satellite missions;
- Remote sensing techniques to monitor flood dynamics;
- The use of remotely sensed data for the calibration, or validation, of hydrological or hydraulic models;
- Data assimilation of remotely sensed data into hydrological and hydraulic models;
- Improvement of river discretization and monitoring based on Earth observations;
- River flow estimation from remote sensing;
- River and flood dynamics estimation from satellite (especially time lag, flow velocity, etc.).

The water cycle or hydrological cycle involves the continuous movement of water on, above, and below the surface of the Earth. In general, hydrological cycle components (e.g., precipitation, evaporation, water storage, and runoff) are characterized by large temporal and spatial variability. Accurate monitoring of various hydrological cycle components and developing hydrological models are important for improving our understanding of hydrological processes. With significant development of sensor technology and sharply growing platforms in past decades, remote sensing offers enhanced capability to monitor various hydrological cycle components at different temporal and spatial scales to complement conventional in situ measurements. Considerable efforts have been made to explore the potentials of remotely sensed data from a vast range of different platforms (e.g., satellite, airborne, drone, ground-based radar) and sensors (e.g., optical, infrared, microwave) in advancing hydrology research, particularly in poorly gauged and ungauged regions. The application of remote sensing in hydrology is expected to increase with enhanced recognition of its potentials and continuous development of advanced sensors (e.g., new satellite missions) and retrieval methods (e.g., innovative machine learning and data assimilation techniques).

The session aims to present and discuss recent advances in the remote sensing of hydrological cycle components as well as the application of remote sensing in hydrological modeling. We encourage studies to investigate the performance of remotely sensed data in multi-variable calibration and spatial evaluation of hydrological models. The added-value of spatially downscaling remotely sensed data in improving hydrological modelling is also particularly welcome.

Agriculture is the largest consumer of water worldwide and at the same time irrigation is one of the sectors where there is one of the hugest differences between modern technology and the largely diffused ancient traditional practices. Improving water use efficiency in agriculture is an immediate requirement of human society for sustaining the global food security, to preserve quality and quantity of water resources and to reduce causes of poverties, migrations and conflicts among states, which depend on trans-boundary river basins. Climate changes and increasing human pressure together with traditional wasteful irrigation practices are enhancing the conflictual problems in water use also in countries traditionally rich in water. Saving irrigation water improving irrigation efficiency on large areas with modern technics is one of the first urgent action to do. It is well known in fact that agriculture uses large volumes of water with low irrigation efficiency, accounting in Europe for around 24% of the total water use, with peak of 80% in the Southern Mediterranean part and may reach the same percentage in Mediterranean non-EU countries (EEA, 2009; Zucaro 2014). North Africa region has the lowest per-capita freshwater resource availability among all Regions of the world (FAO, 2018). Several recent researches are done on the optimization of irrigation water management to achieve precision farming using remote sensing information and ground data combined with water balance modelling.

In this session, we focus on: the use of remote sensing data to estimate irrigation volumes and timing; the management of irrigation using hydrological modeling combined with satellite data; improving irrigation water use efficiency based on remote sensing vegetation indices, hydrological modeling, satellite soil moisture or land surface temperature data; precision farming with high resolution satellite data or drones; farm and irrigation district irrigation management; improving the performance of irrigation schemes; irrigation water needs estimates from ground and satellite data; ICT tools for real-time irrigation management with remote sensing and ground data coupled with hydrological modelling.

This session concerns measurements and estimations of water levels, water extent, water storage and water discharge of surface water bodies, such as rivers, lakes, floodplains and wetlands, as well as groundwater, through the combined use of remote sensing and in situ measurements. Contributions that also cover aspects on assimilation of remote sensing together with in situ data within hydrodynamic models are welcome and encouraged.

The monitoring of river water levels, river discharges, water bodies extent, storage in lakes and reservoirs, and floodplain dynamics plays a key role in assessing water resources, understanding surface water dynamics, characterising and mitigating water related risks and enabling integrated management of water resources and aquatic ecosystems.

While in situ measurement networks play a central role in the monitoring effort, remote sensing techniques are contributing by providing near real time measurements as well as long homogeneous time series to study the impact of climate change, over various scales from local to regional and global.

During the past thirty years a large number of satellites and sensors has been developed and launched allowing to quantify and monitor the extent of open water bodies (passive and active microwave, optical), the water levels (radar and laser altimetry), the global water storage and its changes (variable gravity). River discharge, a key variable of hydrological dynamics, can be estimated by combining space/in situ observations and modelling, although still challenging with available space borne techniques. Interferometric Synthetic Aperture Radar (InSAR) is also now commonly used to understand wetland sheet flow, floodplain dynamics and surface water level changes, with more complex stacking processes to study the relationship between ground deformation and changes in groundwater resources.

Traditional instruments contribute to long-term water level monitoring and provide baseline databases. Scientific applications of more complex technologies like the SAR altimetry on CryoSat-2 and Sentinel-3A/B missions are maturing. The future SWOT mission, to be launched in 2021, will open up many new hydrology-related opportunities.

The Tibetan Plateau and surrounding mountain regions, known as the Third Pole, cover an area of > 5 million km2 and are considered to be the water tower of Asia. The Pan Third Pole expands on both the north-south and the east-west directions, going across the Tibetan Plateau, Pamir, Hindu Kush, Iran Plateau, Caucasian and Carpathian, and covering an area of about 20 million km2. Like the Arctic and Antarctica, the Pan Third Pole’s environment is extremely sensitive to global climate change. In recent years, scientists from around the globe have increased observational, remote sensing and numerical modeling research related to the Pan Third Pole in an effort to quantify and predict past, current and future scenarios. Co-sponsored by TPE (www.tpe.ac.cn), this session is dedicated to studies of Pan Third Pole atmosphere, cryosphere, hydrosphere, and biosphere and their interactions with global change. Related contributions are welcomed.

Many regions worldwide are coping with the climatic global change, which is modifying the water cycle and is increasing the occurrence of extreme hydro-meteorological events. Floods and landslides across a territory could increase significantly respect to actual and past scenarios, causing a modification of the susceptibility of a region and of the frequency of natural hazards.
The use of techniques able to monitor and to improve the prediction of these phenomena at different scales and in scarcely instrumented regions is fundamental. Soil moisture and rainfall estimates measured through remote sensing techniques can furnish reliable and widespread data at different scales. For satellite rainfall measures, state-of-the-art products cover time series of tens of years (e.g., TRMM Multisatellite Precipitation Analysis, Global Precipitation Measurement, EUMETSAT). Regarding soil moisture, different products can bring reliable measurements from a local/landscape to continental scales (e.g., SMMR, AMSR2, SMOS, SMAP, Metop/ASCAT, Sentinel). Innovative products, as soil moisture derived rainfall, allow to retrieve rainfall from different satellite soil moisture products or integrating field measurements of precipitation. Thanks to the improvement of the spatial and temporal resolutions of all of these products, they could become a fundamental tool also for early warning system strategies.
This session aims to collect and present researches concerning the most recent progress on the use of soil moisture and rainfall data from remote sensing for the monitoring and the prediction of landslides and floods. Those phenomena can cause hazards and risks towards population and anthropic elements. We encourage presentations related to:
• inter-comparison and inter-validation between land surface models, remote sensing approaches and in-situ validation networks;
• evaluation and trend analysis of soil moisture or rainfall satellite time series for monitoring landslides or floods and for identifying their possible triggering conditions;
• implementation of satellite measures of rainfall and soil moisture in physically-based or data-driven methods for the prediction of landslides and floods;
• use of remote sensing products of soil moisture and rainfall in early warning system tools;
• use of remote sensing products for investigating the effects of climatic global changes on the susceptibility and hazards towards landslides and floods.

Satellite altimetry provides the possibility to observe key parts of the hydrosphere, namely the ocean, ice, and continental surface water from space. Since the launch of Topex/Poseidon in 1992 the applications of altimetry have expanded from the open oceans to coastal zones, inland water, land and sea ice. Today, seven missions are in orbit, providing dense and near-global observations of surface elevation and several other parameters. Satellite altimetry has become an integral part of the global observation of the Earth‘s system and changes therein.

In recent years, new satellite altimetry missions have been launched carrying new instruments; the CryoSat-2/Sentinel-3 missions equipped with a Delay/Doppler altimeter, the Saral AltiKa mission carrying the first Ka band altimeter, and the 2018 launched six beam photon counting laser altimeter on-board NASAs ICESat-2. Further, new orbits with high inclination and long-repeat time are used for CryoSat-2 and ICESat-2.


Fully exploiting this unprecedented availability of observables will enable new applications and results but also require novel and adapted methods of data analysis.
Across the different applications for satellite altimetry, the data analysis and underlying methods are similar and a knowledge exchange between the disciplines has been proofed to be fruitful.
In this multidisciplinary altimetry session, we therefore invite contributions which discuss new methodology and applications for satellite altimetry in the fields of geodesy, hydrology, cryosphere, oceanography, and climatology.
Topics of such studies could for example be (but not limited to); creation of robust and consistent time series across sensors, validation experiments, combination of radar and laser altimetry for e.g. remote sensing of snow, classification of waveforms, application of data in a geodetic orbit, retracking, or combination with other remote sensing data sets.

Rainfall is a “collective” phenomenon emerging from numerous drops. Understanding the relation between the physics of individual drops and that of a population of drops remains an open challenge, both scientifically and at the level of practical implications. This remains true also for solid precipitation. Hence, it is much needed to better understand small scale spatio-temporal precipitation variability, which is a key driving force of the hydrological response, especially in highly heterogeneous areas (mountains, cities). This hydrological response at the catchment scale is the result of the interplay between the space-time variability of precipitation, the catchment geomorphological / pedological / ecological characteristics and antecedent hydrological conditions. Therefore, (1) accurate measurement and prediction of the spatial and temporal distribution of precipitation over a catchment and (2) the efficient and appropriate description of the catchment properties are important issues in hydrology.

This session will bring together scientists and practitioners who aim to measure and understand precipitation variability from drop scale to catchment scale as well as its hydrological consequences. Contributions addressing one or several of the following topics are especially targeted:
- Novel techniques for measuring liquid and solid precipitation variability at hydrologically relevant space and time scales (from drop to catchment scale), from in situ measurements to remote sensing techniques, and from ground-based devices to spaceborne platforms. Innovative comparison metrics are welcomed;
- Precipitation drop (or particle) size distribution and its small scale variability, including its consequences for precipitation rate retrieval algorithms for radars, commercial microwave links and other remote sensors;
- Novel modelling or characterization tools of precipitation variability from drop scale to catchment scale from various approaches (e.g. scaling, (multi-)fractal, statistic, deterministic, numerical modelling);
- Novel approaches to better identify, understand and simulate the dominant microphysical processes at work in liquid and solid precipitation.
- Applications of measured and/or modelled precipitation fields in catchment hydrological models for the purpose of process understanding or predicting hydrological response.

The assessment of precipitation variability and uncertainty is crucial in a variety of applications, such as flood risk forecasting, water resource assessments, evaluation of the hydrological impacts of climate change, determination of design floods, and hydrological modelling in general. Within this framework, this session aims to gather contributions on research, advanced applications, and future needs in the understanding and modelling of precipitation variability, and its sources of uncertainty.
Specifically, contributions focusing on one or more of the following issues are particularly welcome:
- Novel studies aimed at the assessment and representation of different sources of uncertainty versus natural variability of precipitation.
- Methods to account for different accuracy in precipitation time series, e.g. due to change and improvement of observation networks.
- Uncertainty and variability in spatially and temporally heterogeneous multi-source precipitation products.
- Estimation of precipitation variability and uncertainty at ungauged sites.
- Precipitation data assimilation.
- Process conceptualization and modelling approaches at different spatial and temporal scales, including model parameter identification and calibration, and sensitivity analyses to parameterization and scales of process representation.
- Modelling approaches based on ensemble simulations and methods for synthetic representation of precipitation variability and uncertainty.
- Scaling and scale invariance properties of precipitation fields in space and/or in time.
- Physically and statistically based approaches to downscale information from meteorological and climate models to spatial and temporal scales useful for hydrological modelling and applications.

Hydroclimatic conditions and the availability of water resources in space and time constitute important factors for maintaining an adequate food supply, the quality of the environment, and the welfare of inhabitants, in the context of sustainable growth and economic development. This session is designed to explore the impacts of hydroclimatic variability, climate change, and the temporal and spatial availability of water resources on: food production, population health, the quality of the environment, and the welfare of local ecosystems. We particularly welcome submissions on the following topics:

- Complex inter-linkages between hydroclimatic conditions, food production, and population health, including: extreme weather events, surface and subsurface water resources, surface temperatures, and their impacts on food security, livelihoods, and water- and food-borne illnesses in urban and rural environments.
- Quantitative assessment of surface-water and groundwater resources, and their contribution to agricultural system and ecosystem statuses.
- Spatiotemporal modeling of the availability of water resources, flooding, droughts, and climate change, in the context of water quality and usage for food production, agricultural irrigation, and health impacts over a wide range of spatiotemporal scales.
- Intelligent infrastructure for water usage, irrigation, environmental and ecological health monitoring, such as development of advanced sensors, remote sensing, data collection, and associated modeling approaches.
- Modelling tools for organizing integrated solutions for water, precision agriculture, ecosystem health monitoring, and characterization of environmental conditions.
- Water re-allocation and treatment for agricultural, environmental, and health related purposes.
- Impact assessment of water-related natural disasters, and anthropogenic forcings (e.g. inappropriate agricultural practices, and land usage) on the natural environment; e.g. health impacts from water and air, fragmentation of habitats, etc.

Hydroclimatic variability is an emerging challenge with increasing implications on water resources management, planning, and the mitigation of water-related natural hazards. This variability, along with the continuous development of water demands, and aging water supply system infrastructure make the sustainability of water use a high priority for modern society. In fact, the Global Risk 2015 Report of the World Economic Forum highlights global water crises as being the biggest threat facing the planet over the next decade.

To mitigate the above concerns we need to shed light on hydroclimatic variability and change. Several questions and mysteries are still unresolved regarding natural fluctuations of climate, anthropogenic climate change and associated variability, and changes in water resources. What is a hydroclimatic trend? What is a (long term) cycle? How can we distinguish between a trend and a cycle? Is such discrimination technically useful? How do human activities affect rainfall, hydrological change and water resources availability? How to set priorities and take action to ensure sustainability in light of variability and change?

The objective of this session is to explore hydrological and climatic temporal variability and their connections and feedbacks. More specifically, the session aims to:

1. investigate the hydrological cycle and climatic variability and change, both at regional and global scales;

2. explore the interplay between change and variability and its effect on sustainability of water uses;

3. advance our understanding of the hydrological cycle, benefiting from hydrological records and innovative techniques;

4. improve the efficiency, simplicity, and accurate characterization of data-driven modeling techniques to quantify the impacts of past, present and future hydroclimatic change on human societies; and

5. examine the (un)change to water resources from the recent changes in daily routines due to COVID-19, and how the concept of sustainability is shaping under this threat.

This session is sponsored by the International Association of Hydrological Sciences (IAHS) and the World Meteorological Organization – Commission for Hydrology (WMO CHy) and it is also related to the scientific decade 2013–2022 of IAHS, entitled “Panta Rhei - Everything Flows”.

Extreme hydro-meteorological events drive many hydrologic and geomorphic hazards, such as floods, landslides and debris flows, which pose a significant threat to modern societies on a global scale. The continuous increase of population and urban settlements in hazard-prone areas in combination with evidence of changes in extreme weather events lead to a continuous increase in the risk associated with weather-induced hazards. To improve resilience and to design more effective mitigation strategies, we need to better understand the aspects of vulnerability, risk, and triggers that are associated with these hazards.

This session aims at gathering contributions dealing with various hydro-meteorological hazards that address the aspects of vulnerability analysis, risk estimation, impact assessment, mitigation policies and communication strategies. Specifically, we aim to collect contributions from the academia, the industry (e.g. insurance) and government agencies (e.g. civil protection) that will help identify the latest developments and ways forward for increasing the resilience of communities at local, regional and national scales, and proposals for improving the interaction between different entities and sciences.

Contributions focusing on, but not limited to, novel developments and findings on the following topics are particularly encouraged:
- Physical and social vulnerability analysis and impact assessment of hydro-meteorological hazards
- Advances in the estimation of socioeconomic risk from hydro-meteorological hazards
- Characteristics of weather and precipitation patterns leading to high-impact events
- Relationship between weather and precipitation patterns and socio-economic impacts
- Hazard mitigation procedures
- Strategies for increasing public awareness, preparedness, and self-protective response
- Impact-based forecast and warning systems
- Insurance and reinsurance applications

Urban hydrological processes are characterized by high spatial variability and short response times resulting from a high degree of imperviousness. Therefore, urban catchments are especially sensitive to space-time variability of precipitation at small scales. High-resolution precipitation measurements in cities are crucial to properly describe and analyses urban hydrological response. At the same time, urban landscapes pose specific challenges to obtaining representative precipitation and hydrological observations.

This session focuses on high-resolution precipitation and hydrological measurements in cities and on approaches to improve modeling of urban hydrological response, including:
- Novel techniques for high-resolution precipitation measurement in cities and for multi-sensor data merging to improve the representation of urban precipitation fields.
- Novel approaches to hydrological field measurements in cities, including data obtained from citizen observatories.
- Precipitation modeling for urban applications, including convective permitting models and stochastic rainfall generators.
- Novel approaches to modeling urban catchment properties and hydrological response, from physics-based, conceptual and data-driven models to stochastic and statistical conceptualization.
- Applications of measured precipitation fields to urban hydrological models to improve hydrological prediction at different time horizons to ultimately enable improved management of urban drainage systems (including catchment strategy development, flood forecasting and management, real-time control and proactive protection strategies aimed at preventing flooding and pollution).
- Strategies to deal with upcoming challenges, including climate change and rapid urbanization.

Over the last decades, a significant body of empirical and theoretical work has revealed the departure of statistical properties of hydrometeorological processes from the classical statistical prototype, as well as the scaling behaviour of their variables in general, and extremes in particular, in either state, space and/or time. In the meantime, extremes and more generally the statistics of hydrometeorologic processes are the key input for hydrological applications. As a classic example the estimation of design rainfall should be mentioned. Beside the estimation of the absolute rainfall amount related to a certain return period, the intra-event rainfall distribution, its spatial extension and the rainfall intensities at neighbouring stations can be required, depending on the intended application and thus the analysed scale. But design rainfall is only one among numerous hydrologic applications, which shape the framework for this session.

The estimation of the hydrometeorological extremes and probability distribution, the identification and involvement of supporting information and the hydrologic application over wide range of scales are open challenges, especially under non-stationary conditions. On the other side, hydrometeorologists had never access to so much computer power and data to face these open challenges.

This session welcomes, but is not limited to submissions on:
- Coupling stochastic approaches with deterministic hydrometeorological predictions, in order to better represent predictive uncertainty
- Development of robust statistics under non-stationary conditions for dimensioning purposes
- Development of parsimonious representations of probability distributions of hydrometeorological extremes over a wide range of scales in risk analysis applications and hazard prediction
- Improvements for reliable estimation of extremes with high return periods under consideration of upper or lower limits due to physical constraints
- Linking underlying physics and stochastics of hydrometeorologic extremes
- Exploration of supporting data sets for additional stochastic information (e.g. unintended use of other measurements, citizen scientist data, soft data, …)

An overall aim of the session is to bridge the gap between the theoretical stochastic analysis of hydrometeorological processes and its practical hydrological application.

Hydro-meteorological extremes such as floods, droughts, storms, or heatwaves often affect large regions therefore causing large damages and costs. Hazard and risk assessments, aiming at reducing the negative consequences of such extreme events, are often performed with a focus on one location despite the spatial nature of extreme events. While spatial extremes receive a lot of attention by the media, little is known about their driving factors and it remains challenging to assess their risk by modelling approaches. Key challenges in advancing our understanding of spatial extremes and in developing new modeling approaches include the definition of multivariate events, the quantification of spatial dependence, the dealing with large dimensions, the introduction of flexible dependence structures, the estimation of their probability of occurrence, the identification of potential drivers for spatial dependence, and linking different spatial scales.

This session invites contributions which help to better understand processes governing spatial extremes and/or propose new ways of describing and modeling spatial extremes at different spatial scales.

Target audience: hydrologists, climatologists, statisticians, machine learners, and researchers interested in spatial risk assessments.

Traditionally, hydrologists focus on the partitioning of precipitation water on the surface, into evaporation and runoff, with these fluxes being the input to their hydrologic models. However, more than half of the evaporation globally comes back as precipitation on land, ignoring an important feedback of the water cycle if the previous focus applied. Land-use and water-use changes, as well as climate variability and change alter, not only, the partitioning of water but also the atmospheric input of water as precipitation, related with this feedback, at both remote and local scales.

This session aims to:
i. investigate the remote and local atmospheric feedbacks from human interventions such as greenhouse gasses, irrigation, deforestation, and reservoirs on the water cycle, precipitation and climate, based on observations and coupled modelling approaches,
ii. investigate the use of hydroclimatic frameworks such as the Budyko framework to understand the human and climate effects on both atmospheric water input and partitioning,
iii. explore the implications of atmospheric feedbacks on the hydrologic cycle for land and water management.

Typically, studies in this session are applied studies using fundamental characteristics of the atmospheric branch of the hydrologic cycle on different scales. These fundamentals include, but are not limited to, atmospheric circulation, humidity, hydroclimate frameworks, residence times, recycling ratios, sources and sinks of atmospheric moisture, energy balance and climatic extremes. Studies may also evaluate different sources of data for atmospheric hydrology and implications for inter-comparison and meta-analysis. For example, observations networks, isotopic studies, conceptual models, Budyko-based hydro climatological assessments, back-trajectories, reanalysis and fully coupled earth system model simulations.

Development and application of decision support systems to enhance sustainable feedbacks between anthropogenic activities and the natural functioning of aquifers and underground reservoirs requires reliable methods to infer key parameters controlling multiphase flow and contaminant fluxes of conservative or reactive chemicals in subsurface environments. These systems are complex and extremely heterogeneous exhibiting variations on a multiplicity of scales.
Addressing heterogeneity in all its manifestations is the focus of exciting and intense forefront scientific research and industrial activities.

This session
- invites presentations on recent developments in understanding, measuring, and modelling subsurface flow and solute transport processes in both the saturated and unsaturated zones, as well as across boundaries between these;
- is aimed at providing an opportunity for specialists to exchange information and to introduce various existing and novel alternative deterministic and stochastic models of subsurface flow and transport to the general hydrological community, with critical and timely applications to environmentally and industrially relevant scenarios.

Focus is placed on recent key developments in novel theoretical aspects and associated computational tools, fate of new contaminants, and field/laboratory applications dealing with accurate and efficient prediction and quantification of uncertainty for flow, conservative and reactive transport processes in the subsurface, in the presence of multiple information at different scales, ranging from the pore level to the intermediate and basin scales.

A number of physical (e.g. flow and transport), chemical (e.g. red-ox reactions) and biological (e.g. bio-mineralization) mechanisms critically control the fate of the underground environment where rocks, liquids, gases and microbes sit in close proximity and interaction. The common feature of these processes is their heterogeneity (spatial variability) and the different scale at which they impact the natural environment. A wide range of innovative methods have recently emerged, from laboratory experiment to field tests, that are capable of quantifying the extent and the interaction between physical, chemical and biological properties of complex structures at different scales, including: (hydro)geophysical methods, innovative sensors or microscopic imaging techniques.

The objective of this session is to discuss significant improvement in our understanding of subsurface processes based on innovative methods allowing the quantification of relevant phenomena and their underling mechanisms such as flow, transport, chemically driven or biologically mediated processes in heterogeneous porous and fractured media. Contributions may include, for example, imaging, advanced in-situ single- and/or cross-borehole hydraulic tests, hydrogeophysical techniques, strategies for borehole/borehole interval sealing or inverse model techniques. We particularly encourage integrative interdisciplinary methods, i.e. hydraulic, chemical or heat methods that elucidate the role played by the flow heterogeneity on transport and related processes. Ideas for future strategies related to experimental methods and interpretation of existing data are welcomed.

This session combines presentations on recent developments in understanding, measuring, and modeling subsurface flow and transport. We aim to include processes in both the saturated and unsaturated zones, as well as across boundaries at different scales. At the same time, we address unsolved problems related groundwater contamination management as risk assessment and remediation.

The correct quantification of transport processes, which occur at different spatial and temporal scales, is challenging. It strongly influences predicted spreading, dilution and mixing rates. However, dispersion, mixing and chemical reactions are local phenomena that strongly depend on the interplay between large-scale system heterogeneity and smaller-scale processes. Much effort has been placed in the fundamental understanding of these processes since they are of practical relevance to identify the fate of contaminants in surface and subsurface water that can affect human health and the environment. Particularly newly emerging contaminants of such as PFASs, pharmaceuticals, pesticides, or nanoparticles are increasingly being detected at low levels in surface- and groundwater. Some of these anthropogenic chemicals are potentially harmful can produce long-term adverse health effects even at very low levels of exposure.

The aim of this session is to discuss the effect of flow heterogeneity on transport at different scales, from pore scale up to catchment scale - including theory, modeling, laboratory and field experiments as well as applications. Our contributions deal with the questions: Is macrodispersivity a meaningful parameter? Under which conditions does spatially variable flow enhance mixing and chemical reactions? What is the role played by diffusive processes in modeling transport in porous media? How to upscale dispersion and reactive transport from pore to field-scale? What is the relation between ADE models and dynamic structures of catchment hydrology like travel time distributions? What are appropriate methods to characterize the relevant aquifer properties? What are the recent improvements in transport measurement technologies? What is the best way to physically and chemically characterize sites contaminated by anthropogenic chemicals? What is their mobility and persistence in both the unsaturated and unsaturated zones? How can we improve remediation through laboratory and field research?

The session is co-sponsored by the Groundwater Commission of IAHS.

Dissolution, precipitation and chemical reactions between infiltrating fluid and rock matrix alter the composition and structure of the rock, either creating or destroying flow paths. Strong, nonlinear couplings between the chemical reactions at mineral surfaces and fluid motion in the pores often leads to the formation of intricate patterns: networks of caves and sinkholes in karst area, wormholes induced by the acidization of petroleum wells, porous channels created during the ascent of magma through peridotite rocks. Dissolution and precipitation processes are also relevant in many industrial applications: dissolution of carbonate rocks by CO2-saturated water can reduce the efficiency of CO2 sequestration, mineral scaling reduces the effectiveness of heat extraction from thermal reservoirs, acid rain degrades carbonate-stone monuments and building materials.

With the advent of modern experimental techniques, these processes can now be studied at the microscale, with a direct visualization of the evolving pore geometry. On the other hand, the increase of computational power and algorithmic improvements now make it possible to simulate laboratory-scale flows while still resolving the flow and transport processes at the pore-scale.

We invite contributions that seek a deeper understanding of reactive flow processes through interdisciplinary work combining experiments or field observations with theoretical or computational modeling. We seek submissions covering a wide range of spatial and temporal scales: from table-top experiments and pore-scale numerical models to the hydrological and geomorphological modelling at the field scale. We also invite contributions from related fields, including the processes involving coupling of the flow with phase transitions (evaporation, sublimation, melting and solidification).

Particles (inorganic particles, biocolloids, plastics) in environmental systems are of great concern because of their potential adverse effects on ecosystem functions, wildlife and human health. They may also alter the transport properties of dissolved contaminants and change the hydraulic properties of subsurface systems. On the other hand, engineered particles and biocolloids play an important role in site remediation and aquifer restoration. This interdisciplinary session fosters the exchange among scientists from hydrogeology, microbiology, ecotoxicology, engineering, and analytical chemistry in order to provide a general picture of the occurrence and fate of natural and engineered particles in aquatic and terrestrial systems.

We are expecting contributions in the following fields:
• occurrence, fate and transport of biocolloids, nanoparticles and other particles (microplastics, soot, ...) in aquatic and terrestrial systems
• methods to detect, characterize, and quantify particles in
 aquatic and terrestrial systems
• advanced experimental methods to test the behaviour of particles in aquatic and terrestrial systems (mesocosms, non-invasive imaging, ...)
• interactions between biocolloids, particles and solid surfaces
• biocolloid biodegradation in the presence of solids
• toxicity of products generated from biological disruption of pollutants in the presence of biocolloids
• adverse effects of nanoparticles on microorganisms
• effects of climate change on biocolloid and nanoparticle migration
• public health risks associated with water and air polluted with biocolloids and nanoparticles.

Thermal, hydraulic and mechanical processes in aquifers are of increasing interest for hydrogeological analysis for development of innovative field and laboratory experiments. Both in research and in practice, accurate characterization of subsurface flow and heat transport, observations of induced or natural variations of the thermal regime. The seasonal and long-term development of thermal and mechanical conditions in aquifers, and heat transfer across aquifer boundaries are focus points. This also includes the role of groundwater in the context of geothermal energy use for predicting the long-term performance of geothermal systems (storage and production of heat), and integration in urban planning. There are many ongoing research projects studying heat as a natural or anthropogenic tracer, and which try to improve thermal response testing in aquifers. Such techniques are of great potential for characterizing aquifers, flow conditions, and crucial transport processes, such as mechanical dispersion. Understanding the interaction of hydraulic, thermal and mechanical processes is a major challenge in modern hydrogeology. Deep underground constructions, tunnels, CO2 storage, hydro- and enhanced geothermal applications are prominent subjects. We invite contributions that deliver new insight into advances in experimental design, reports from new field observations, as well as demonstration of sequential or coupled modeling concepts. The session aims to provide an overview of the current and future research in the field, covering any temporal or spatial scale, and seeks to address both separate and coupled processes.

This session deals with the use of geophysical methods for the characterisation of subsurface properties, states, and processes in contexts such as hydrology, agriculture, contaminant transport, etc. Geophysical methods potentially provide subsurface data with an unprecedented high spatial and temporal resolution in a non-invasive manner. However, the interpretation of these measurements is far from straightforward in many contexts and various challenges remain. Among these, the need for improved quantitative use of geophysical measurements in model conceptualisation and parameterisation, and the need to move quantitative hydrogeophysical investigations beyond the laboratory and field scale towards the catchment scale. Therefore, we welcome submissions addressing advances in the acquisition, processing, analysis and interpretation of data obtained from geophysical and other minimally invasive methods applied to a (contaminant) hydrological context. In particular, we encourage contributions on innovations in experimental and numerical methods in support of model-data fusion, including new concepts for coupled and joint inversion, and improving our petrophysical understanding on the link between hydrological and geophysical properties.

The session aims to bring together scientists studying various aspects related to groundwater flow systems, and their role in solving water management and environmental problems.
Understanding groundwater flow systems requires knowledge of the governing processes and conditions from the local to regional and basin-scales, including porous and fractured porous media. Moreover, problems connected to groundwater management underline the importance of sustainable development and protection of groundwater resources.
In this context of groundwater flow understanding, the session intends to analyze issues connected to groundwater management and its protection from degradation with respect to quantity and quality (e.g. due to overexploitation, conflicts in use, climate change, resource development or contamination). Papers related to methods of defining groundwater flow, and preventing, controlling and mitigating harmful environmental impacts related to groundwater, including those in developing countries, are also welcome.

Climate change is regarded as one of the most important challenges humankind faces today. Groundwater has been an important buffer against climate variability for millennia, providing a secure water-supply in many parts of the world. Despite the potential role of groundwater storage in climate change adaptation strategies, the actual impact of climate change on groundwater resources remains highly uncertain. The pathways through which changes in natural (e.g., evaporation, transpiration and rainfall) and human factors (e.g., groundwater abstractions) impact groundwater resources are only partially understood due to the complexity and the many (unknown) feedback mechanisms of the subsurface system. This session aims to focus on the questions: How are different processes affected by climate change and how do they impact groundwater resources? How to implement climate change in our groundwater studies to predict its impact?

We are looking for a broad range of studies on above listed aims, with a special interest in processes and models. We especially encourage (but do not limit to) contributions from one of the following topics:

- Impact of climate change on groundwater recharge (e.g. through changes in rainfall, evaporation, transpiration, etc.).
- Impact on salinity and water availability in coastal aquifers due to sea level changes and dilution.
- Impact on groundwater extremes (both droughts and high groundwater levels).
- Changes in dilution potential or leaching potential for contaminants including pesticides and nutrients.
- Studying the feedback between groundwater and climate through coupled models.
- Human impacts on groundwater resources under a changing climate.
- Methodological studies showcasing how to implement climate change into subsurface models, including uncertainties of the projections.
- Comparative studies using different approaches/models to study climate change impacts.

This session is co-organized by the Commission on Groundwater and Climate Change (CGCC) of the IAH.

Groundwater is the world's most important, best protected and most exploited freshwater resource. It is intensively used by humans. It is also the primary source for drinking water supply and irrigation, hence critical to the global water-food-energy security nexus, especially in dry regions. Groundwater is sensitively to shifts in climate, which changes the hydrological cycle and thus groundwater recharge. Additionally, global changes such as population growth or changes in land use affect groundwater resources, both in terms of quantity and quality. Due to these changes, regions with high water stress are expected to expand globally. Beside regions that have already a water deficit, new regions, such as catchments in Central Europe with continental climate and decreasing precipitation in summer periods are likely to be subjected to water stress. The Mediterranean basin is also expected to become a major hot spot of water stress in the future.
Therefore, groundwater resources, especially in dry regions, need to be managed wisely, protected and especially used sustainably. In this session we invite contributions, which identify new consequences of a changing environment for better future management, protection, and sustainable use of groundwater. This implies adapted modelling techniques, such as coupling climate models with hydrological models, coupling climate models with soil water- and groundwater models. This includes also studies into groundwater quantity and quality changes and recharge mechanisms. In addition, we invite contributions from appropriate field observational studies.

Furthermore, the session asks for contributions that address regional strategies for groundwater sustainability, in detail that (i) unravel the combined action of topography, geology, climate, land use and anthropogenic forcing in controlling regional groundwater availability, quality and sustainability; and (ii) propose new methods (e.g., coupled modelling approaches) for assessing and managing regional groundwater systems in diverse climatic, hydrologic, socio-economic and institutional settings, and accounting for uncertainty; (iii) present appropriate field observational studies; (iv) address uncertainty and limited data availability due to a frequently associated data scarcity issue in dry regions, methodologies, strategies.

Estimates of the Mean Residence Time (MRT) or age distributions of groundwater can be used to understand the flow and storage characteristics of aquifers including impacts of subsurface heterogeneity, surface-groundwater interactions, groundwater recharge dynamics and many other processes.
Hence they are valuable tools to protect groundwater dependent eco-systems, to estimate the vulnerability and the recovery-time of groundwater bodies impacted by pollution, to define drinking water protection areas and planning the sustainable use of water resources, to quantify quality problems due to climate change impacts.
The session wants to bring together experience of applied resource management and advanced research using a wide range of different techniques (tracer techniques, modelling, etc.) and to estimate groundwater age-distributions in variable aquifers at various spatial scales.

Karst environments are characterized by distinctive landforms and unique hydrological behaviors. Karst systems are commonly extremely complex, heterogeneous and very difficult to manage, because their formation and evolution are controlled by a wide range of geological, hydrological, geochemical and biological processes. Furthermore, karst systems are extremely vulnerable due to the direct connection between the surface and subsurface through the complex networks of conduits and caves.

The great variability and unique connectivity may result in serious engineering problems: on one hand, karst groundwater resources are easily contaminated by pollution because of the rapidity of conduit flow; on the other hand, the presence of karst conduits that weakens the strength of the rock mass may lead to serious natural and human-induced hazards. The design and development of engineering projects in karst environments thus should necessarily require: 1) an enhanced understanding of the natural processes governing the initiation and evolution of karst systems through both field and modelling approaches, and 2) specific interdisciplinary approaches aimed at mitigating the detrimental effects of hazardous processes and environmental problems.

This session calls for abstracts on research related to geomorphology, hydrogeology, engineering geology, hazard mitigation in karst environments in the context of climate change and increasing human disturbance.

Understanding complex infiltration and recharge dynamics within the vadose zone still represents a huge challenge in modern hydro(geo)logy. Soils and fractured consolidated materials are by nature heterogeneous at all spatial scales. The spatial organization of their porous structure and associated material properties play a major role in controlling infiltration dynamics and transport processes in the vadose zone. Furthermore, preferential pathways, such as macropores, fracture networks and faults may strongly affect travel time distributions, system vulnerability, connectivity of surface- subsurface ecosystems, and require adapted strategies in the context of groundwater management. Experimental approaches for the comprehensive recognition of the subsurface structures and the associated flow and transport processes at sufficiently small spatial scales often lack the required resolution. In addition, numerical models that often operate on catchment scales are typically unable to fully account for the sub-scale heterogeneity of the systems material properties. However, depending on thickness and heterogeneity of the vadose zone a proper identification of pathway activation, inter-continuum exchange processes and storage behavior is mandatory, yet often neglected, for accurate modeling studies. Specifically, in fractured-porous media, where the unsaturated zone may reach a thickness of several hundred meters, rapid and locally focused flows are an important driver for rapid recharge dynamics. Innovative experimental and numerical approaches can improve our ability to map and represent the relevant subsurface structures, leading to an improved simulation of water fluxes and hence to a more comprehensive process understanding. This session welcomes studies with a focus on elaborate analytical/numerical methods, field studies and laboratory experiments. This includes experimental approaches for mapping soil heterogeneity and consolidated subsurface structures, numerical approaches for representing heterogeneity in numerical models, identification of relevant structures at different spatial scales and methodological advances leveraging measurement data to infer heterogeneity through data assimilation or machine learning. Furthermore, we welcome studies that target complex infiltration processes including interaction dynamics of macropores/fractures and porous matrix systems under saturated and variably-saturated on field to laboratory scales.

Vadose zone hydrology studies the physical processes in the unsaturated zone. Modeling and observation of soil and vadose zone processes aims at characterizing soil properties and quantifying terrestrial water storage dynamics. The states of soil, air and water affect biogeochemical processes, vegetation water availability, nutrient and pollutant transport at local scale, catchment response functions and rainfall-runoff processes at intermediate scale, land-atmosphere interaction and land-climate feedbacks at the continental scale. Advanced measurement techniques, increased availability of high-frequency data, and the need for terrestrial system understanding challenges vadoze zone modeling concepts, budging model parameterizations from static to near dynamic. This session aims to bring together scientists advancing the current status in modelling soil and vadose zone processes from the pore to the catchment and continental scale. Contributions to this session address soil hydrological processes, characterization of soil properties and soil hydraulic properties, soil biogeochemical processes and their interactions with hydrology, transport of pollutants, and soil vegetation atmosphere modelling.

The interactions between plants and the environment play a prominent role in terrestrial fluxes and biochemical cycles, but we still lack a general understanding of how these interactions impact plant growth and plant access to soil resources particularly under deficient conditions. The main challenge arises from the complexity of both soil and plants. To address such a knowledge gap, an improved understanding and predictability of plant-related transfer processes are urgently needed.
Emerging experimental techniques such as non-invasive imaging technique and system modeling tools have deepened our insights into the functioning of water and solute transport processes in the soil-plant system. Quantitative approaches that integrate across disciplines and scales constitute stepping stones to foster our understanding of fundamental biophysical processes at the frontier of soil and plants.
This session targets researchers investigating plant-related resource transfer processes across different scales (from the rhizosphere to the global scale) and welcomes scientists from multiple disciplines ranging from soil to plant sciences. We are specifically inviting contributions of:
- Measuring and modeling of water and solute fluxes across soil-plant-atmosphere continuum at different scales.
- Novel experimental and modeling techniques assessing below-ground plant processes such as root growth, root water, and nutrient uptake, root exudation, microbial interactions, and soil aggregation
- Measuring and modeling of soil-plant hydraulics
- Bridging the knowledge gap between biologically and physically oriented research in soil and plant sciences
- Identification of plant strategies to better access and use resources from soil under abiotic stress
- Mechanistic understanding of drought impact on transpiration and photosynthesis and their predictions by earth system model

The proper management of water resources is a key aspect of soil conservation in arid and semiarid environments, where any irrigation activity is structurally and deeply related to the understanding of soil hydrological behaviour. In these areas, irrigation should be regarded to as a fundamental element of any agroecosystem and an effective defence against desertification. Its importance goes beyond the technological aspects, often being traditional irrigation a cultural heritage, which requires to be faced with an (at least) interdisciplinary approach which involves also humanities. On the other hand, improper practices may contribute to soil degradation. As an example irrigation may lead to soil salinization, with dramatic fallout on agricultural productivity, and overgrazing may lead soil to compaction, with negative effects on the soil capability of water buffering.

This session welcomes contributions ranging from the understanding of the soil hydrological behaviour and of the mass fluxes, through the soil, in arid and water—scarce environments and also under stress conditions (e.g. water shortage, compaction, salinization), to the interaction between soil hydrology and irrigation, and to the design of irrigation systems in arid districts and oases, including also the use of non—conventional waters (e.g. water harvesting). Particular attention will be given to the maintenance and improvement of traditional irrigation techniques as well as to precision irrigation techniques, also with local community involvement. Interdisciplinary contributions, which deal with different aspects and functions of the link between soil hydrology and irrigation techniques in arid environments, are encouraged.

This session is co-sponsored by the International Commission on Irrigation and Drainage (ICID).

Obtaining quantitative information on the spatial pattern of soil redistribution during storms and on the spatial sources supplying sediment to rivers is required to improve our understanding of the processes controlling these transfers and to design effective control measures. It is also crucial to quantify the transfer or the residence times of material transiting rivers along the sediment cascade, and to reconstruct the potential changes in sources that may have occurred at various temporal scales. During the last few decades, several sediment tracing or fingerprinting techniques have contributed to provide this information, in association with other methods (including soil erosion modelling and sediment budgeting). However, their widespread application is limited by several challenges that the community should address as priorities.
We invite specific contributions to this session that address any aspects of the following:
• Developments of innovative field measurement and sediment sampling techniques;
• Soil and sediment tracing techniques for quantifying soil erosion and redistribution;
• Sediment source tracing or fingerprinting studies, using conventional (e.g. elemental/isotopic geochemistry, fallout radionuclides, organic matter) or alternative (e.g. colour, infrared, particle morphometry) approaches;
• Investigations of the current limitations associated with sediment tracing studies (e.g. tracer conservativeness, uncertainty analysis, particle size and organic matter corrections);
• Applications of radioisotope tracers to quantify sediment transit times over a broad range of timescales (from the flood to the century);
• The association of conventional techniques with remote sensing and emerging technologies (e.g. LiDAR);
• Integrated approaches to developing catchment sediment budgets: linking different measurement techniques and/or models to understand sediment delivery processes.

The transfer of sediments and associated contaminants play an important role in catchment ecosystems as they directly influence water quality, habitat conditions and biogeochemical cycles. Contaminants may include heavy metals, pesticides, nutrients, radionuclides, and various organic, as well as organometallic compounds. The environmental risk posed by sediment-bound contaminants is largely determined by the sources and rate at which sediments are delivered to surface water bodies, the residence time in catchments, lakes and river systems as well as biogeochemical transformation processes. However, the dynamics of sediment and contaminant redistribution is highly variable in space and time due to the complex non-linear processes involved. This session thus focuses on sources, transport pathways, storage and re-mobilization, and travel times of sediments and contaminants across temporal and spatial scales as well as their impact on catchment and freshwater ecosystems.

This session particularly addresses the following issues:
- Delivery rates of sediments and contaminants from various sources (i.e. agriculture, urban areas, mining, industry or natural areas);
- Transport, retention and remobilization of sediments and contaminants in catchments and river reaches;
- Modelling of sediment and contaminant transport on various temporal and spatial scales;
- Biogeochemical controls on contaminant transport and transformation;
- Studies on sedimentary processes and morphodynamics, particularly sediment budgets;
- Linkages between catchment systems and lakes, including reservoirs;
- Analysis of sediment archives to appraise landscape scale variations in sediment and contaminant yield over medium to long time-scales;
- Impacts of sediments and contaminants on floodplain, riparian, hyporheic and other in-stream ecosystems;
- Response of sediment and contaminant dynamics in catchments, lakes and rivers to changing boundary conditions and human actions.

Sedimentary processes in aquatic environments, including entrainment, transport and deposition of sediment by hydrodynamic mechanisms, are key features for various research disciplines, e.g. geomorphology and paleoclimatology or hydraulics and river engineering. An accurate evaluation of entrainment, transport and deposition rates, conditioning river channel morphology and bed composition, is fundamental for an adequate development of conceptual sediment budget models and for the calibration and validation of numerical tools.
The main goal of this session is to bring together the community of scientists, scholars and engineers, investigating, teaching and applying novel measurement techniques and monitoring concepts, which are crucial to determine sedimentary and hydro-morphological processes in rivers, lakes and reservoirs, estuaries as well as in coastal and maritime environments. Within the focus of this session are the evaluation and quantification of bed load and suspended load, flocculation, settling, and re-suspension of such processes relevant to morphological channel changes as bed form development, horizontal channel migration, bed armouring and colmation.
Contributions are welcome with a particular focus on single and combined measurement techniques, on post-processing methods as well as on innovative and advanced monitoring concepts for field applications. Furthermore, we welcome contributions containing recent results in a temporal and spatial scale on sediment budgets as well as on sedimentary and morphodynamics processes in open water environments.
Contributions may refer, but are not restricted, to:
- measurements of suspended sediment transport in open water environments, e.g. with optical, acoustical, traditional sampling methods or others;
- measurements of bed load transport, e.g. with bed load samplers, sediment traps, tracers or acoustic and optical methods;
- determination of sediment characteristics, e.g. with mechanical bed material samplers or freeze core technique;
- measurements of critical bed shear stress of cohesive sediments, e.g. with benthic flumes or miscellaneous devices;
- monitoring of morphological changes like lake and reservoir sedimentation, bank erosion or bed armouring, meandering migration, river bends evolution;
- measuring networks / multiple point datasets;
- monitoring concepts including case studies;
- in-situ as well as laboratory calibration of measurement data;

Complex hydro-morphological processes, such as sediment erosion, transport, deposition or fan development, affect open water environments, including rivers, estuaries as well as lakes and reservoirs. Consequently, many research tasks as well as practical applications rely on the correct prediction of these processes. During the last decades, numerical models have become a powerful tool in the research fields of hydraulic engineering and geosciences to simulate these hydro-morphological processes. With improved algorithms as well as an ever growing computational power, it became feasible to simulate the interaction of water, sediments and air with high resolution in space and time. In addition, with an increasing quantity and quality of validation data from laboratory experiments and field studies, numerical models are continuously enhanced so that many good examples of sediment transport modelling offer new insights in multiphase processes, e.g. dune development, river bed armoring or density driven transport. Hence, new generations of numerical modelling techniques open up the possibility to explore numerous outstanding research questions related to hydro-morphologic processes.
The main goal of this session is to bring together scientists and engineers, who develop, improve, and apply numerical models of multiphase flows for sediment transport in open water environments. We invite contributions that deal with numerical modelling from small-scale, such as bed structure development, to large-scale interactions, such as long-term development of hydro-morphological processes in rivers, lakes, reservoirs and estuaries.
Contributions may refer, but are not restricted, to:
• Entrainment processes of sediments (from cohesive sediments to armoured river beds)
• Bed load and suspended sediment transport processes (including flocculation processes)
• Simulation of sediment management including planning, operation and maintenance of hydro power plants
• Design and evaluation of restoration measures to revitalize rivers
• Navigation issues, such as sediment replenishment, dredging and erosion induced by ship generated waves
• Flood related issues of long term effects of morphological bed changes on flood security
• Eco-hydraulics such as flow – sediment – vegetation interaction
• Density driven transport

Water and sediments interact at different spatial and temporal scales in freshwaters promoting the development of highly dynamic systems. Erosion, transport and sedimentation are vital processes that shape river morphology. These dynamic processes, in turn, are essential to provide a mosaic of diverse habitat patches for aquatic species and to freshwater ecosystems functioning.
Anthropogenic activities such as flow regulations or dams lead to fragmentation and ecosystem degradation, interfering with natural hydro-morphodynamics and affecting aquatic ecology. In Europe, large efforts are set to restore disturbed river sections to meet the goals of a good ecological status, set by the Water Framework Directive. Experience to date indicates that integrating both physical and ecological processes in river restoration efforts is critical to freshwater ecosystems conservation. In this context, the interdisciplinary field of Ecohydraulics represents the link between abiotic components (e.g. hydrology, hydraulics, geomorphology) and riverine biota (e.g. vegetation, fish, macroinvertebrates). Advances in this field of research are therefore paramount to make future management decisions in freshwater systems.
This session aims at integrating the core research disciplines forming Ecohydraulics, from hydrology, hydraulics, fluvial geomorphology, and biology, but also social aspects to ensure a holistic assessment of rivers, lakes and reservoirs, and to enable the implementation of sustainable restoration measures.
We welcome both fundamental and applied research, presenting approaches at different spatio-temporal scales. They may include holistic tools and methods to improve the assessment, prediction and management of restoration and mitigation measures in aquatic systems, with a focus on the hydrological, fluvial geomorphological, and biological interactions.
Contributions may refer, but are not restricted, to:
- sediment transport, fluvial dynamics and sediment budgets in rivers
- risk analysis and mitigation in fluvial systems
- reservoir sedimentation: processes and management
- large wood and microplastic in aquatic systems
- nature-compatible river engineering and river development
- nature based solutions
- revitalization of river systems (from successful studies to failures in restoration)
- tools and methods (concepts, measurements, monitoring, modelling) to understand the interactions between fluvial processes and their biological responses

Debris flows are among the most dangerous natural hazards that threaten people and infrastructures in both mountainous and volcanic areas. The study of the initiation and dynamics of debris flows, along with the characterization of the associated erosion/deposition processes, is of paramount importance for hazard assessment, land-use planning and design of mitigation measures, including early warning systems. In addition, the impacts of climate change on debris-flow activity must be considered and carefully analysed, as the number of mountain areas prone to these events may increase in future.
A growing number of scientists with diverse backgrounds are studying debris flows and lahars. The difficulties in measuring parameters related to their initiation and propagation have progressively prompted research into a wide variety of laboratory experiments and monitoring studies. However, there is a need of improving the quality of instrumental observations that would provide knowledge for more accurate hazards maps and modeling. Nowadays, the combination of distributed sensor networks and remote sensing techniques represents a unique opportunity to gather direct observations of debris flows to better constrain their physical properties.
Scientists working in the field of debris flows are invited to present their recent advancements. In addition, contributions from practitioners and decision makers are also welcome. Topics of the session include: field studies and documentation, mechanics of debris-flow initiation and propagation, laboratory experiments, modeling, monitoring, impacts of climate change on debris-flow activity, hazard and risk assessment and mapping, early warning, and alarm systems.

The session aims to discuss hydrological and geomorphological processes related to deformation of natural slopes as well as human-modified slopes both on local and regional scale. It focuses on the detailed monitoring, analysis and modelling of hydrological and geomorphological processes required to improve our understanding and prediction of the spatio-temporal patterns of both triggering factors and slope deformation mechanisms.

The session also focuses on landslide early warning systems (LEWSs) at both regional and local scales. The session wishes to highlight operational approaches, original achievements and developments useful to operate reliable (efficient and effective) local and territorial LEWS. Moreover, the different schemes describing the structure of a LEWS available in literature clearly highlight the importance of both social and technical aspects in the design and management of such systems.

For the above-mentioned reasons, contributions addressing the following topics are welcome:
• hydrological and geomorphological processes
• rainfall thresholds definition;
• monitoring systems for early warning purposes;
• warning models for warning levels issuing;
• performance analysis of landslide warning models;
• communication strategies;
• emergency phase management;
• landslide risk perception.

Ecohydrology, i.e., the study of the interactions between water and ecosystems, is expanding rapidly as a field of research, beyond traditional discipline boundaries in terms of questions and approaches. This session aims to draw examples from this wide field, in order to portray the current diversity and common features of research frontiers in ecohydrological studies, as well as the range of methods employed. We thus encourage contributions showing novel results or methods when tackling questions related to the coupling of ecological, biogeochemical and hydrological processes, at scales ranging from the single organ or organisms to whole ecosystem/catchment. While contributions relative to all terrestrial and aquatic systems are welcome, this year we especially encourage abstracts focusing on managed ecosystems, showing how human intervention alters the interactions between water and ecosystems.

This session provides a platform for transdisciplinary science that addresses the continuum of the river and its catchment to the coastal sea. We invite studies across geographical borders; from the source to the sea including groundwater, and across the freshwater-marine water transition, including estuaries, deltas and marshlands. The session particularly welcomes studies that link environmental and social science, addressing the impacts of climate change and extreme events and impact of human activities on water and sediment quality and quantity, hydromorphology, biodiversity, ecosystem functioning and services of River-Sea continua. Such a systems approach is required to develop solutions for sustainable management of River-Sea social-ecological systems.

We need to fully understand how River-Sea Systems function. How are River-Sea continua changing due to human pressures? What is the impact of processes in the catchment on coastal and marine systems function, and vice versa? How can we discern between human-induced changes or those driven by natural processes from climate-induced variability and extreme events? What will the tipping points of socio-ecologic system states be and what will they look like? How can we better characterise river-sea systems from the latest generation Earth observation to citizen science based observatories. How can we predict short and long term changes in River-Sea-Systems to manage them sustainably? What is the limit to which it is possible to predict the natural and human-influenced evolution of River-Sea-Systems? The increasing demand to jointly enable intensive human use and environmental protection in River-Sea Systems requires holistic and integrative research approaches with the ultimate goal of enhanced system understanding as the knowledge base for sustainable management solutions.

Vegetation, soils and water resources have interacted and co-evolved over Millions of years, shaping our current ecohydrological systems. Vegetation still responds rapidly to changing environmental conditions, including rising atmospheric carbon dioxide concentrations, climate change, soil degradation and hydrologic modifications. Prediction of these co-evolutionary and adaptive processes is a major scientific challenge, as it requires understanding of the general underlying principles and constraints governing plant-environment interactions.

This session aims to bring together collected knowledge about organising principles guiding co-evolutionary processes in biology, hydrology and physics, including theoretical, modelling, observational and experimental studies. We solicit contributions to all aspects of our quantitative understanding of principles such as natural selection, relevant thermodynamic principles (e.g. MaxEnt, maximum power, maximum entropy production) or biological optimality and the associated cost-benefit trade-offs.

Evapotranspiration (ET) is the key water flux at the interface of soil, vegetation and atmosphere. In-situ measurements to estimate ET (and its individual components evaporation and transpiration) have been developed in different research disciplines and cover a range of scales, from the point scale of individual sap flow sensors in trees over pedon-scale lysimeters to eddy covariance footprints. Each estimate and each scaling step includes a method-specific set of uncertainties which are rarely communicated. This is problematic for connecting different methods and the effort to scale up to remote sensing products from satellites or to model resolutions.

This session will mainly focus on the variety of ET estimates from different in-situ devices such as lysimeters, sap flow sensors, eddy covariance stations, scintillometers, approaches like the Bowen ratio method and others, including reporting and comparing the respective uncertainties of the methods. Additionally, we want to address the scale dependency of the various approaches and the scale gap between in-situ ET data, remote sensing products and catchment- or landscape-scale modelled ET. We welcome contributions that (1) assess and compare established and new in-situ ET measurements, (2) address uncertainty in the respective methods, (3) analyse trends as well as spatial and temporal patterns in in-situ measured ET data, (4) include cross-scale comparisons and scaling approaches and (5) incorporate in-situ measurements into modeling approaches.

Stable isotopes are powerful tools for tracing fluxes of water and associated nutrients in the soil-plant-atmosphere continuum. They are increasingly used by various disciplines to better understand the functioning of the soil-plant-atmosphere system. While new methods allow measurements at high spatial and temporal resolution, studies applying tracer methods are now tackling complex interactions between soil processes, plant physiology and ecology, and variable atmospheric drivers. As such, methodological developments and changes are happening quickly and have a strong bearing on process understanding and interpretation of findings. This session aims to address the current state of the art for methods, applications, and process interpretations using stable isotopes in the critical zone and to foster interdisciplinary exchange. We welcome experimental and modeling studies that present methodological developments and applications of isotope tracers to improve the actual knowledge of the water and nutrient exchanges at the soil-plant-atmosphere interfaces. Studies that seek to cross disciplinary boundaries and reveal new eco-hydrological process understanding are especially welcome.

Peatlands develop in specific hydrological settings and react sensitively to changes in climatic and hydrological boundary conditions. The hydrology of peatlands is fundamental to their function and development. Soil hydrological properties can change drastically after human interventions such as drainage, causing challenges for both model parameterization and re-wetting measures. Pristine peatlands offer and regulate many ecosystem services such as biodiversity, carbon storage, and nutrient retention. Hydrology is a key control for a number of these services. Furthermore, the effects of peatlands (both pristine and disturbed) on flood retention and regional climate are much debated. As hydrological and biotic processes in peatlands are strongly coupled, estimating the eco-hydrological response of peatlands under climate change and linking it to vegetation development and greenhouse gas emissions is a demanding task for modelers.

This session focuses on:
(1) hydrological processes operating in all types of peatlands (pristine, disturbed, degraded, drained, managed, rehabilitated or re-wetted) in northern and tropical latitudes, and
(2) the first-order control of peatland hydrology on all kinds of peatland functions.

We aim to boost knowledge transfer across spatial/temporal scales and methods; from the pore to the global scale, including laboratory, field, remote sensing, and modeling studies on hydrological, hydrochemical, biogeochemical, ecohydrological or geophysical topics, as well as ecosystem service assessments.

Groundwater-surface water interfaces (e.g., hyporheic and benthic zones and riparian corridors) are integral components of the aquifer-river or aquifer-lake continuum. Interactions between groundwater and surface water lead to strong bi-directional influences between surface waters, aquifers and interconnecting hyporheic zones. A rapidly expanding number of research projects are now investigating the implications of hyporheic exchange on the transport and transformation of nutrients and contaminants within river networks, and on controls to heat, oxygen, and organic matter budgets available to microorganisms and macroinvertebrates in streambed sediments. However, there is still a need to better understand the links between physical, biogeochemical, and ecological process dynamics in groundwater-surface water interfaces and their implications for fluvial ecology or limnology, respectively. Furthermore, it is important to consider the response of hyporheic exchange fluxes to environmental and climatic controls at different spatial and temporal scales (e.g. river channel, alluvial aquifer, regional groundwater flow). We consider up- and downscaling and the development of a general conceptual framework and improved process understanding for groundwater-surface water interfaces as among the most urgent challenges of hyporheic zone research. Consequently, we particularly welcome contributions that aim to close these knowledge gaps and solicit both experimental and modelling studies with a focus on:

- The development and application of novel experimental methods to investigate physical, biogeochemical and ecological conditions at the groundwater-surface water interface in rivers, lakes, riparian corridors, and wetlands;

- Investigations of the role of hyporheic processes for the retention and natural attenuation of nutrients and pollutants, particularly with respect to impacts on surface water and groundwater quality;

- Hydrological, biogeochemical and ecological modelling approaches (e.g. transient storage models, coupled groundwater-surface water models etc.);

- Investigations of the implications of groundwater-surface water interactions for management and risk assessment frameworks with regard to the European Water Framework Directive.

Invited Speaker: ‪Eugènia Martí‬

As confined water bodies with limited exchanges, lakes and inland seas are particularly vulnerable to climatic and human impacts accumulated over broad catchment areas. Hence, they mirror both the global change effects and
anthropogenic pressures, perhaps, stronger than any other aquatic objects. Lakes and inland seas
also play an important role in ecosystem services such as fisheries, aquaculture, tourism, and others. These multifunctional roles require careful governance measures to avoid hydrological and environmental deterioration.
Research of lakes and inland seas admits many common approaches and techniques. Oceanographic methodology and instrumentation are often applicable to limnological studies. Reciprocally, insights obtained from lakes can also be instructive with respect to marine systems. This interdisciplinary session provides a joint forum for oceanographers, limnologists, and hydrologists interested in processes governing physical, chemical, and biological regimes of various lakes and inland seas of the world, as well as their responses to climate change and anthropogenic impacts.

Tropical ecosystems are biomes of global significance due to their large biodiversity, carbon storage capacity, and their role in the hydrological cycle. Historic and recent human activities have, however, resulted in intensive transformation of the tropical ecosystems in the Amazon, Central America, Central Africa and in South East Asia impacting the cycling of nutrient, carbon, water, and energy. Understanding their current functioning at process up to biome level in its pristine and transformed state is elemental for predicting their response upon changing climate and land use, and the impact this will have on local up to global scale.
This session aims at bringing together scientists who investigate the functioning of the tropical ecosystems across spatial and temporal scales by means of remote and in-situ observational, modelling, and theoretical studies. Particularly welcome are presentations of novel, interdisciplinary approaches and techniques.

The shorter return period of climate and hydrological extremes has been observed in the changing climate, which affects the distribution and vitality of ecosystems. In many regions, available water is a crucial point of survival, especially in forests. Risk can be enhanced by the exposure and/or by the vulnerability of the affected ecosystem as well as by land use/land cover change.
The session should provide a multidisciplinary platform for sharing experiences and discussing results of local and catchment scale case studies from a wider range of relevant fields such as
• observed impacts and damage chains in natural, agricultural, and forest ecosystems induced by droughts and intense rainfall events;
• correlation between the underlying environmental factors (e.g. climate, soil parameters, topographic factors) and the distribution/vitality of ecosystems;
• integrated application or comparison of databases and methods for the identification and complex assessment of ecosystem responses to abiotic stress factors;
• contribution to the increase of knowledge of adaptive forestry, the sustainability of management, and the conservation and improvement of mixed forests to support rural development;
Contributions are encouraged from international experiences, ongoing research activities as well as national, regional, and local initiatives.

The critical zone comprises the Earth's permeable near-surface layer from the top of the canopy to the bottom of the groundwater. It is the zone where hydrosphere, atmosphere, pedosphere and geosphere interact with the biosphere. This fragile skin of our planet, which supports the life and survival of humans maintaining food production and drinking water quality, is endangered by threats such as climate change and land use change.
New approaches and innovative modeling strategies are needed to understand these complex interactions between hydrological, biogeochemical cycles and human resilience processes that may govern critical zone system dynamics, including sources, dynamics and chemistry of water, models to quantify external influences like human activities or erosion, weathering rate, water transfer in the frame of global change and biolological feedback mechanisms.

This session focuses on the advancing proxies that may address pressing interdisciplinary scientific questions in coupling various disciplines like hydrology, soil science and biogeochemistry that cover single-site investigations, targeted experiments, remote sensing studies, large data compilations and modelling. This will be illustrated in this session through studies regarding the critical zone as a whole or within its different compartments, including the different environmental processes (geological, physical, chemical, and biological), their couplings and reactive transport modeling, and exploring the cities resilience.

Writing a scientific paper is an essential part of research, and is a skill that needs practice.

This session is organized in cooperation with the Young Hydrologic Society (http://younghs.com/).

In 2018, hydrologists from all over the world outlined twenty-three questions that remain unresolved by the scientific community, named Unsolved Problems in Hydrology (UPH). The discussion around them highlighted the need for science driven by technological innovations that is outcome- and/or product-specific. The EGU GA represents a meaningful opportunity for researchers to meet up and share their ideas, although sometimes the scale of the event makes it difficult to actually talk about future projects and develop research proposals. In this Call for Calls session, participants will engage in a sprint-like, competitive event where they will come up with innovative ideas to contribute to the solution of at least one of the UPH.

The session will provide the right atmosphere where researchers can discuss and think about a specific problem, and brainstorm initial ideas to gather information to write an abstract. Attendees are expected to make as much progress as possible. After the session, the participants will be able to continue working if needed. The expected outcome is a project with introduction and plan of action, including outputs such as a paper or collaboration, which will be presented as a short abstract and delivered before 5 pm CEST on the final day of EGU.

Given that the UPH encompasses issues across the hydrological system and human interactions, this session is open to all researchers in water resources and water security. Early-career scientists are particularly encouraged to participate to apply and enhance their current expertise and expand their research network.

Forecasting and Early Warning Systems (EWSs) help societies prepare for and respond to all types of disasters, including those due to hydro-meteorological hazards. In recent years, there has been a consensus on the need for an interdisciplinary approach to forecasting, and communicating warnings and their inherent uncertainties. The integration of methods and knowledge such as risk, probabilistic and risk-based forecast, impact-based assessments, Information and Communication Technology (ICT) fields, social science and local knowledge can (1) improve the quality of forecast, (2) improve decision making and (3) support better communication of warnings and response. However, one of the biggest challenges is the need to collaborate across relevant disciplines. Therefore new ways of thinking are required on the necessary skills to facilitate more collaborative work.

This short course aims to highlight the benefits and skills required for an interdisciplinary approach in EWS in the form of a role-playing game and discussion. Participants will have the opportunity to understand more about the role of diverse disciplines, their importance in EWS and most importantly, collaborate with people from different backgrounds to come up with a successful solution. The game will be based on a hypothetical emergency situation, in which participants will be required to make decisions based on their assigned role. After the game, an active discussion with all participants will be carried out to propose take away action points on how to improve interdisciplinarity in EWS and how Early Career Scientist (ECS) can contribute to promoting this approach.
At the end of the short course participants should have:
(1) increased awareness and understanding of the roles of EWS actors
(2) Understanding of the necessity to engage and collaborate with professionals from different backgrounds
(3) Newly acquired skills to improve interdisciplinary working and communication

We especially encourage, but not limit, the participation of Early Career Scientists (ECS) interested in the field of Natural Hazards Social, Hydrological and Atmospheric Sciences as well as those who are already working or have in interest working in interdisciplinary fields.
This short course is organised by the Early Warning Systems Young Professionals (EWSYP) Network and the Water Youth Network (WYN)

Data assimilation combines observational data with a numerical model. It is commonly used in numerical weather prediction, but is also applied in oceanography, hydrology and other areas of Earth system science. By integrating observations with models in a quantitative way, data assimilation allows to estimate model states with reduced uncertainty, e.g. to initialize model forecasts. Also, it can estimate parameters that control processes in the model or fluxes. Hence, it can provide information about non-observable quantities if the model represents those. The combination of modeled and observed data requires error estimates for both sources of information. In ensemble data assimilation the error in the model state is estimated by an ensemble of model state realizations. This uncertainty estimate is then used by the assimilation method like the ensemble Kalman filter or a particle filter.

To simplify the implementation and use of ensemble data assimilation, the Parallel Data Assimilation Framework (PDAF) has been developed. PDAF is a freely available open-source software (http://pdaf.awi.de) that provides ensemble-based data assimilation methods like the ensemble Kalman filter, but also allows to perform pure ensemble simulations. PDAF can be used from small toy problems running on notebook computers up to high-dimensional Earth system models running on supercomputers.

The course will, after a short introduction to the ensemble data assimilation methodology, provide a hands-on and interactive example of building a data assimilation system based on a simple numerical model. This practical introduction will prepare the participants to build a data assimilation system for their numerical models with PDAF and hence provide a quick start for applying ensemble assimilation to their individual problems.

This course is both for the novices as well as for data-assimilation experts. It will be useful for novices who have a modelling application and observations and are interested in applying data assimilation, but haven't found a starting point yet. Data-assimilation experts who want to enhance the performance of their applications, or are keen to accelerate development of new data-assimilation methods and new applications will also benefit from the course.

For the interactive hands-on example we will provide source code for download at http://pdaf.awi.de/EGU2021 from April 19.

GEOframe is a system for doing hydrology by computer (https://abouthydrology.blogspot.com/2015/03/jgrass-newage-essentials.html).  It is based on the OMS3/CSIP infrastructure, developed by USDA- ARS/Colorado State University.  OMS3/CSIP allows to build models by components, which perform simple task that can be joined together to build “Modelling Solutions”, suited to particular case studies. Components developed so far cover: meteorological data interpolation (Bancheri et al., 2018), terrain analysis (Abera et al., 2014), calibration tools (Formetta et al., 2011; Formetta et al., 2014), rainfall-runoff models (Bancheri et al., 2020; Formetta et al., 2014), evaporation and transpiration models, snow models (Formetta et al., 2014), Richards’ equations solvers, runoff propagation.

The modelling solution components are executed in parallel by the OMS3/CSIP engine. Besides, a further parallelization is made thanks to the spatial discretisation of the catchments in hydrological response units. GEOframe has been applied to catchments from few thousands of square meters to two hundred thousand square kilometers, and it is also used for operational forecasting in the Basilicata region in Italy. 

The short course introduces the system using some case studies already prepared and show how to join components, set the parameters, run the calibration and obtain results. The course will be based on the material already prepared for various Winter Schools on the topic, which allows the participants to use independently the system.

Bayesian approach to probability theory and statistics has various applications in hydrological sciences, particularly to solve inversion problems and to characterize model uncertainty. From calibrating a hydrological model to quantifying catchment transit time distribution, Bayesian approaches incorporate prior system knowledge that helps us to improve our understanding of the natural system. Using a number of practical case studies, this short course aims at providing a state-of-the-science overview of the usage of Bayesian statistics in different facets of hydrological modeling.

We kindly invite early career researchers (MSc students, PhD candidates, post-doctoral researchers) to attend this short course designed to address the fundamentals of Bayesian statistics and its particular applications in hydrology.

This will be the sixth year that the Hydroinformatics for Hydrology short course takes place during the EGU conference. Information to this and former short course topics can be found online on the homepage of the cooperating Young Hydrologic Society (http://younghs.com).

During the recent years, it has become more and more obvious that soil structure plays a fundamental role in regulating processes in soils. As soil structures are hierarchical, complex and highly variable, studies involving soil structures require a relatively large number of replicate samples. Three-dimensional X-ray imaging provides an excellent tool to map out soil structure, but image analyses are still time intensive and require experience. This limits the number of X-ray images, and thus replicate samples that can be analyzed within reasonable time scales. SoilJ is an open-source and free plugin for the open-source image processing software ImageJ. It is tailor-made for the analyses X-ray images of soil and aims at automatizing the necessary image processing and analyses steps. This course gives a short introduction into X-ray image processing and analyses in general and specifically with SoilJ, provides an overview about SoilJ functionalities and offers guidance for researchers interested in participating in developing their own plugins. In the second part of this short course, hands-on for X-ray image analyses is offered.

R is an open-source, versatile programming language that is suitable for multi-scale analyses from just a few observations to big data and high-performance computing. It has a growing, enthusiastic user-base (including hydrologists) that is responsible for a continuous stream of ever more efficient and useful packages and workflows.

Running for its fourth year, this EGU short course, co-organised by the Young Hydrologic Society (younghs.com), will introduce and showcase a selection of both core and recently developed R packages that can be applied to data analyses in hydrology, as well as other scientific disciplines.

The course will be delivered by hydrologists with wide experience in subjects including: hydrological modelling (including flood and drought analysis), forecasting, statistics, and eco-hydrology. Topics covered in this years’ course include:
• Data retrieval
• Extremes modelling
• Hydrological modelling
• Hydrological forecasting
• Machine learning
• Open discussion and QA

This course contributes new topics to those delivered in previous years, building upon the openly accessible Github repository for hydrologists using R in their work (https://github.com/hydrosoc).

You have observed timeseries or observed fields from hydroclimatic variables (e.g., rainfall, wind, etc.) or from other environmental variables. You wish to generate synthetic ones that reproduce precisely the observed statistical properties, but you do not how to do it. No worries! Join us and you will find out!

The short course will introduce you to a unified method of stochastic modelling and the CoSMoS R-package that makes generation of random fields and of univariate or multivariate time series piece of cake. The generated random fields or time series preserve any desired probability distribution and correlation structure including features like spatial and temporal intermittency. We will talk about the stochastic properties of hydroclimatic processes such as precipitation, streamflow, wind, temperature, etc., and highlight features such as stationarity, cyclostationarity, marginal distributions, spatiotemporal correlations structures, and intermittency. We will explain how AR and multivariate AR models work and describe step-by-step the parent-Gaussian framework that allows precise and easy simulation of random fields and time series. Real-world examples include rainfall simulation at different spatiotemporal scales as well as simulating variables such as temperature, relative humidity, etc.

Early Career Scientists (ECS) and student are more than welcome! As always, we organize this short course in cooperation with the Young Hydrologic Society (YHS; younghs.com)!

Nature-based Solutions (NBS) are reframing discussion and policy responses worldwide to environmental challenges. Thus, NBS is of growing implementation, supported namely by the EU political agenda (e.g., green deal), as a way to attain the United Nations (UN) Sustainable Development Goals (SDG), and to reinforce the New Urban Agenda. The NBS concept recognise the importance of nature and outline requirements for a systemic and holistic approach to environmental change, based on an understanding of the structure and functioning of ecosystems, and the social and institutional context within which they are situated. Furthermore, there is a growing recognition that human activities exert pressure on natural resources affecting the ecosystem dynamics and therefore the nexus (synergies and trade-offs) between their different functions and services. However, quantification of existing NBS’ effectiveness, their operationalisation and replication in different environmental settings has not been presented in such a way that allows them to be both widely accepted and incorporated in policy development and in practical implementation to achieve the UN SDGs.
This session aims to discuss and advance knowledge of innovative NBS approaches to face environmental challenges, such as water supply and management, agricultural production and healthy ecosystems, and simultaneously provide better understanding of associated social-ecological interactions, contributing to enhance the scientific basis for sustainable development and resilience.
This session seeks to:
- Better understanding of advantages and disadvantages of NBS to address global environmental and societal challenges;
- Studies on adaptation and mitigation options for the effect of climate change on water provisioning and livelihoods;
- New methods and tools to investigate the role of NBS in the context of environmental change; in particular, the effectiveness of NBS for hydro-meteorological risk reduction at landscape/watershed scale;
- New insights, methodologies, tools and best practices enabling successful implementation and upscaling of NBS in multiple contexts;
- Identifying opportunities for and barriers to NBS within current regulatory frameworks and management practices;
- Presenting overviews and case studies of NBS projects that also involve the private sector and market-based mechanisms;
- NBS towards achieving the Sustainable Development Goals (SDGs).

Citizen science (the involvement of the public in scientific processes) is gaining momentum across multiple disciplines, increasing multi-scale data production on Earth Sciences that is extending the frontiers of knowledge. Successful participatory science enterprises and citizen observatories can potentially be scaled-up in order to contribute to larger policy strategies and actions (e.g. the European Earth Observation monitoring systems), for example to be integrated in GEOSS and Copernicus. Making credible contributions to science can empower citizens to actively participate as citizen stewards in decision making, helping to bridge scientific disciplines and promote vibrant, liveable and sustainable environments for inhabitants across rural and urban localities.
Often, citizen science is seen in the context of Open Science, which is a broad movement embracing Open Data, Open Technology, Open Access, Open Educational Resources, Open Source, Open Methodology, and Open Peer Review. Before 2003, the term Open Access was related only to free access to peer-reviewed literature (e.g., Budapest Open Access Initiative, 2002). In 2003 and during the “Berlin Declaration on Open Access to Knowledge in the Sciences and Humanities”, the definition was considered to have a wider scope that includes raw research data, metadata, source materials, and scholarly multimedia material. Increasingly, access to research data has become a core issue in the advance of science. Both open science and citizen science pose great challenges for researchers to facilitate effective participatory science, yet they are of critical importance to modern research and decision-makers. To support the goals of the various Open Science initiatives, this session looks at what is possible and what is applied in Earth Science.

We want to ask and find answers to the following questions:
Which approaches can be used in Earth Sciences?
What are the biggest challenges in bridging between scientific disciplines and how to overcome them?
What kind of participatory citizen scientist involvement and open science strategies exist?
How to ensure transparency in project results and analyses?
What kind of critical perspectives on the limitations, challenges, and ethical considerations exist?