The science-policy interface is not just as a way to increase the impact of our science, but it is also a scientific subject in itself. It presents several challenges to both scientists and policy-makers. They include understanding the different steps in the policy cycle: from setting the agenda to formulating, adopting, implementing, monitoring and evaluating polices. It is also crucial to know which facts and evidences are most needed at each step, so scientists can provide the best information at the right time and in the best way.

This session provides the opportunity for discussing with policy makers and addressing the necessary skills to facilitate the uptake of hydrological sciences in policy formulation and implementation.

This session will host invited-talks only and an interactive online/onsite panel discussion with the audience.

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?

4. Understanding of complex human-water systems and their management: what are the feedback mechanisms of emergent phenomena in human-water systems? What are the benefits and shortcomings based on empirical, conceptual or model-based research and disciplinary perspective? How can we enable stakeholders to avoid unintended consequences of water management decisions?

This session welcomes abstracts that consider how to observe, model and analyse interactions of people and water, and the effects of social and environmental changes on hydrological systems. It is organised as part of the IAHS Panta Rhei hydrological decade 2013-2022; and focuses on gains in our understanding of dynamic human-water systems.
Examples of relevant areas include:

- Observations of human impacts on, and responses to, hydrological change.
- Interactions of communities with local water resources.
- Hydrological models that include anthropogenic effects.
- Creation of databases describing hydrology in human-impacted systems.
- Data analysis and comparisons of human-water systems around the globe and especially in developing and emerging countries.
- Human interactions with hydrological extremes, i.e. floods and droughts, and water scarcity.
- The role of gender, age, and cultural background in the impacts of hydrological extremes (floods and droughts), risk perception, and during/after crises and emergencies.
- innovative modelling for exploring the interplay, feedback, and interactions between hydrological extremes and public and private adaptation actions;
- integration of models and observations for advancing knowledge on the human-water systems;
- new frameworks to support risk-based decision-making in case of multi-hazards;

Groundwater, the hidden component of the water cycle, traditionally receives less attention than surface water from both the scientific community and policy makers, due to it being "out of sight, out of mind". However, this precious resource is inextricably linked to the maintenance of natural ecosystems and human well-being. Groundwater has always been part of the lives of worldwide communities: irrigated agriculture is primarily sustained by groundwater resources, particularly in arid and semi-arid regions; holy wells and sacred springs are part of our global cultural heritage, while disagreement over groundwater resources have previously resulted in turmoil and national/transboundary conflicts. These obvious interconnections, however, are neglected in favour of the development of sectorial approaches to groundwater resource assessment.
Socio-hydrogeology has recently been proposed as an effective approach to addressing complex groundwater-related issues in an increasingly holistic and integrated manner. By focusing on the reciprocity between humans and groundwater, it aims to explore and understand their dynamic interactions and feedbacks with a final goal of developing transdisciplinary solutions for transdisciplinary problems. Due to the more "personal" (i.e., individual household/community supplies) and local nature of groundwater in many instances, socio-hydrogeology seeks to understand individuals and communities as a primary source, pathway and receptor for potable groundwater supplies, including the role of local knowledge, beliefs, risk perception, tradition/history, and consumption. In essence, the “socio” in socio-hydrogeology embodies sociology, including social, cognitive, behavioural and socio-epidemiological science.

For this session we encourage contributions from diverse fields, including:
• Examples of socio-hydrogeological assessments (e.g., participatory monitoring, stakeholder engagement, public participation, citizen science)
• Integration of “non-expert” knowledge and experience within quantitative and qualitative hydrogeological studies
• Challenges and opportunities arising from the integration of hydrogeology and social sciences
• Social and political approaches to water resources research
• Groundwater geoethics and national/transboundary conflicts
• Attempts to integrate behavioural, experiential or knowledge-based data with hydrogeological/health risk assessment models
• Educational goals for future socio-hydrogeologists

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 to an Arduino or Raspberri Pi? Used the new Lidar in the new iPhone to measure something relevant for hydrology? 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. Recent extreme heat and flood events are clear demonstrations of how our planet’s climate is changing, underlining the significance of water both as a threat and as an increasingly volatile resource.
The accurate and timely measurement of streamflow is therefore more critical than ever to enable the management of water for ecology, for people and industry, for flood risk management and for understanding changes to the hydrological regime. Despite this, effective monitoring networks remain scarce, under-resourced, and often under threat on a global scale. Even where they exist, observational networks are increasingly inadequate when faced with extreme conditions, and lack the precision and spatial coverage to fully represent crucial aspects of the hydrological cycle.

This session aims to tackle this problem by inviting presentations that demonstrate new and improved methods and approaches to streamflow monitoring, including:
1) Innovative methodologies for measuring/modelling/estimating river stream flows;
2) Real-time acquisition of hydrological variables;
3) Remote sensing and earth observation techniques for hydrological & morphological monitoring;
4) Measurement in extreme conditions associated with the 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.

Many papers have advised on carefully considering the methods we choose for our modelling studies as they potentially affect our modelling results and conclusions. However, there is no common and consistently updated rulebook on what good modelling practice is and how it has evolved since e.g. Klemes (1986), Refsgaard & Henriksen (2004) or Jakeman et al. (2006). In recent years several papers have proposed useful practices such as benchmarking (e.g. Seibert et al., 2018), controlled model comparison (e.g. Clark et al., 2011), careful selection of calibration periods (e.g. Motavita et al., 2019) and methods (e.g. Fowler et al., 2018 ), or testing the impact of subjective modelling decisions along the modelling chain (Melsen et al., 2019). However, none of the proposed methods have become quite as common and indispensable as the split sample test (KlemeŠ, 1986), despite their very justified existence.

This session hopes to provide a platform for a visible and ongoing discussion on what ought to be the current standard for an appropriate modelling protocol to acquire robust and reliable results considering uncertainty in all its facets. We aim to bring together, highlight and foster work that applies, develops, or evaluates procedures for a robust modelling workflow or that investigates good modelling practices. We invite research that aims to improve the scientific basis of the entire modelling chain and puts good modelling practice in focus again. This might include (but is not limited to) contributions on:

(1) Benchmarking model results
(2) Developing robust calibration and evaluation frameworks
(3) Going beyond common metrics in assessing model performance and realism
(4) Conducting controlled model comparison studies
(5) Developing modelling protocols
(6) Investigating subjectivity along the modelling chain
(7) Uncertainty propagation along the modelling chain
(8) Communicating model results and their uncertainty to end users of model results
(9) Evaluating implications of model limitations and identifying priorities for future model development and data acquisition planning

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.

Eric Wood passed away November 3, 2021. His career spanned five decades. It included early work in systems analysis applications to hydrology dating to his dissertation research at MIT in the 1970s, scaling in the 1980s and 1990s, hydrologic remote sensing beginning with planning for NASA’s Earth Observing System in the 1980s and 1990s, continental hydrology beginning in the 1990s, and hyper-resolution land surface modeling in the mid-2000s, with a "call upon the international hydrologic community and the hydrological science support infrastructure to endorse the effort" and face this "grand challenge" [1]. A hallmark of Eric's career was strong international collaborations, especially with European scientists, notably with his most recent contribution to the development of the End-to-end Demonstrator for improved decision-making in the water sector in Europe (EDgE) for the Copernicus Climate Change Service [2]. Eric Wood attended almost all previous EGU meetings (most recently, the GA in 2019), and was awarded the 2007 John Dalton Medal of the Hydrological Sciences division, and the Union's 2014 Alfred Wegener Medal & Honorary Membership. This session will review Eric's main contributions to hydrology, from data to models, highlighting the experience of former students, postdocs, and colleagues that his life touched.

[1] Wood et al.: Hyperresolution global land surface modeling: Meeting a grand challenge for monitoring Earth's terrestrial water; https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2010WR010090
[2] Samaniego et al.: Hydrological Forecasts and Projections for Improved Decision-Making in the Water Sector in Europe; https://journals.ametsoc.org/view/journals/bams/100/12/bams-d-17-0274.1.xml

Water is a strategic issue in the African and Mediterranean regions, mainly because of the scarcity of the available resources in quantity and/or quality. The Mediterranean and African climates and the surface hydrology are characterized by a strong variability in time and space and the importance of extreme events droughts and floods. During the last century, changes of all kinds and intensities, including in the agricultural sector have affected surface and underground reservoirs and water uses. 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 intends to identify and analyse the changes in the Mediterranean and Africa hydrology, in terms of processes, climate and other water-related topics, including environmental and food security. It will gather specialists in observation and modelling of the various water fluxes and redistribution processes within the catchments. Case studies showcasing practical experiments and innovative solutions in decision making under large uncertainty are ncouraged. 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.

Forests are recognized as prime regulators of the hydrological cycle. Changes in their structure cause 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 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, especially concerning long-term experimental setups and monitoring networks.

Anthropogenic intervention is exerting ever-increasing pressure on natural ecosystems, affecting water quantity and quality, and 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. Answering these open questions 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 modellers to submit contributions investigating hydrological processes in forests from boreal to tropical regions, including water quality, the carbon cycle, or ecohydrological aspects.

This session welcomes studies that:
1) Improve our understanding of hydrological processes in forested catchments and the resilience of forested catchments to environmental changes and disturbances;
2) Assess the hydrological-related impacts of land use/cover change on forested systems;
3) Present new methods (e.g. remote sensing techniques) or tools that unveil new perspectives or data sources in forest hydrology;
4) Include interdisciplinary research that holistically integrates data and models from soil–plant–atmosphere experimental or modelling schemes into 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 ground water 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.

Water stored in the snow pack and in glaciers represents an important component of the hydrological budget in many regions of the world, as well as a sustainment to life during dry seasons. Predicted impacts of climate change in catchments covered by snow or glaciers (including a shift from snow to rain, earlier snowmelt, and a decrease in peak snow accumulation) will reflect both on water resources availability and water uses at multiple scales, with potential implications for energy and food production.

The generation of runoff in catchments that are impacted by snow or ice, profoundly differs from rainfed catchments. And yet, our knowledge of snow/ice accumulation and melt patterns and their impact on runoff is highly uncertain, because of both limited availability and inherently large spatial variability of hydrological and weather data in such areas. This translates into limited process understanding, especially in a warming climate.

This session aims at bringing together those scientists that define themselves to some extent as cold region hydrologists, as large as this field can be. Contributions addressing the following topics are welcome:
- Experimental research on snow-melt & ice-melt 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 or in-situ snow products 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 dynamics or the application of techniques for tracing water flow paths;
- Studies on cryosphere-influenced mountain hydrology, such as landforms at high elevations and their relationship with streamflow, water balance of snow/ice-dominated mountain regions;
- Studies addressing the impact of climate change on the water cycle of snow and ice affected catchments.

Large data samples of diverse catchments can provide insights into relevant physiographic and hydroclimatic factors that shape hydrological processes. Further, large data sets increasingly cover a wide variety of hydrologic conditions, enabling the development of several research topics, such as extreme events, data and model uncertainty, hydrologic model evaluation and prediction in ungauged basins.
This session aims to showcase recent data and model-based efforts on large-sample hydrology, which advance the characterization, organization, understanding and modelling of hydrological diversity. We specifically welcome abstracts that seek to accelerate progress on the following topics:

1. Development and improvement of large-sample data sets:
How can we address current challenges on the unequal geographical representation of catchments, quantification of uncertainty, catchment heterogeneities and human interventions for fair comparisons among datasets?
2. Catchment similarity and regionalization:
Can currently available global datasets be used to define hydrologic similarity? How can information be transferred between catchments?
3. Modelling capabilities:
How can we improve hydrological modelling by using large samples of catchments?
4. Testing of hydrologic theories:
How can we use large samples of catchments to transfer hydrologic theories from well-monitored to data-scarce catchments?
5. Identification and characterization of dominant hydrological processes:
How can we use catchment descriptors available in large sample datasets to infer dominant controls for relevant hydrological processes?
6. Human impacts and non-stationarity
How can we use large samples of catchment data to infer hydrological response under changing environmental conditions?

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

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

Understanding and representing hydrological processes is the basis for developing and improving hydrological and Earth system models. Relevant hydrological data are becoming globally available at an unprecedented rate, opening new avenues for modelling (model parametrization, evaluation, and application) and process representation. As a result, a variety of models are developed and trained by new quantitative and qualitative data at various temporal and spatial scales.
In this session, we welcome contributions on novel frameworks for model development, evaluation and parametrization across spatio-temporal scales.

Potential contributions could (but are not limited to):
(1) introduce new global and regional data products into the modeling process;
(2) upscale experimental knowledge from smaller to larger scale for better usage in catchment models;
(3) advance seamless modeling of spatial patterns in hydrology and land models using distributed earth observations;
(4) improve model structure by representing often neglected processes in hydrological models such as human impacts, river regulations, irrigation, as well as vegetation dynamics;
(5) provide novel concepts for improving the characterization of internal and external model fluxes and their spatio-temporal dynamics;
(6) introduce new approaches for model calibration and evaluation, especially to improve process representation, and/or to improve model predictions under changing conditions;
(7) develop novel approaches and performance metrics for evaluating and constraining models in space and time

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

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, pollutant concentration, or stable isotope) 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 using a large sample of catchments helps to improve our understanding of the model functioning in relation to catchment processes. The use of multiple data sources in data-driven approaches can help engineering data-driven models with higher predictability skills. Finally, the quantification of multiple uncertainty sources enables the identification of their contributions and this is critical for uncertainty reduction and decision making under uncertainty.
This session welcomes contributions that apply one or more of the multi-aspects in hydrological, ecological and water quality studies. In particular, we seek studies covering the following issues:
• Frameworks using multi-objective or multi-variables to improve the identification (prediction) of hydrological, ecological or water quality models;
• Studies using multi-model or multiple-data-driven approaches;
• Use of multiple scales, sites or large-sample studies 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.
• Application of machine learning and data mining approaches to learn from large, multiple or high-resolution data sets.

The importance of soil moisture for the hydrological systems dynamics is undebated. A great deal of observations and research have been invested in the last decades to improve the knowledge of soil water status as well its spatial and temporal variation within a given hydrological system. In that effort, several types of soil moisture data have become available, spanning from in-situ observations, radar data, cosmic ray studies to several satellite products.

Although spatial and temporal patterns of soil moisture are the result of processes that hydrological models typically capture, the application of the currently available soil moisture information for improving models is progressing only slowly. This is partly due to a gap between the information content provided by the available data and the information required to improve models. Furthermore, some essential parts of soil water storage at the larger scale, like that of the root zone, is typically assessed using combination of models and data, resulting in a lack of independent information for validation.

This session invites contributions dealing with closing these gaps. This could, for example, be achieved by progress in the descriptions of the processes causing the spatial and temporal variations in soil moisture or by more efficiently using information from available data to improve model predictions across scales. The session is explicitly open for research across all relevant hydrological scales: local, hillslope, catchment up to the continental scale, and deal with both the vertical and lateral flow processes.

Examples for suitable contributions are (but are not limited to):
- The role of soil moisture in the functioning of hydrological systems
- Methods and case studies on improving the predictive power of models using soil moisture data
- Deriving process knowledge from soil moisture data that can be used to improve hydrological models
- Evaluating the suitability of given soil moisture data types for representing hydrologic processes

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

Water quantity and quality is typically assessed and managed at the scales of catchments and aquifers. However, flow and transport integrate a multitude of hydrological transport and biogeochemical reaction processes interacting at different temporal and spatial scales, and thus hampering the understanding of underlying cause-effect relationships.
Recent advances in high-frequency measurements, machine learning, and the use of age tracers and their modelling have enhanced process understanding of flow and transport in catchments and aquifers. Our session brings together studies approaching this challenge from different angles and with different tools:
- Data-driven interpretation of water quality time series observed at the catchment outlet
- Isotope- and model-driven evaluation of transit times and water ages in catchments including the groundwater compartment
- Linkages of water transit times, hydrochemical and ecohydrological response

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.

The occurrence of pathogens and an exponentially increasing number of contaminants in freshwater and estuary environments pose a serious problem to public health. This problem is likely to increase in the future due to more frequent and intense storm events, the intensification of agriculture, population growth and urbanization. Pathogens (e.g., pathogenic bacteria and viruses) are introduced into surface water through the direct discharge of wastewater, or by the release from animal manure or animal waste via overland flow or groundwater, which subsequently presents potential risks of infection when used for drinking, recreation or irrigation. Contaminants of emerging concern are released as diffuse sources from anthropogenic activities or as discharges from wastewater treatment plants (e.g., trace organic contaminants). So far, the sources, pathways and transport mechanisms of fecal indicators, pathogens and emerging contaminants in water environments are poorly understood, and thus we lack a solid basis for quantitative risk assessment and selection of best mitigation measures. Innovative, interdisciplinary approaches are needed to advance this field of research. In particular, 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 aim to close these knowledge gaps and include both small and large-scale experimental and modelling studies with a focus on:
- The development and application 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

A large number of pathogens, micropollutants and their transformation products (veterinary and human pharmaceuticals, personal care products, pesticides and biocides, chlorinated compounds, PFAS, 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. Modelling 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. Mitigation measures can help reduce contamination of ground- and surface water and impacts on water quality and aquatic ecosystems.

This session invites contributions that improve our quantitative understanding of the sources and pathways, mass fluxes, the fate and transport and the mitigation 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
- Setup of mitigation measures and evaluating their effectiveness.

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 and local 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.

Bayesian approaches have become increasingly popular in water quality modelling, thanks to their ability to handle uncertainty comprehensively. This is particularly relevant in environmental decision making where Bayesian inference enables to consider the reliability of predictions of the consequences of decision alternatives, alongside uncertainties related to decision makers’ risk attitudes and preferences, uncertainty related to system understanding and random processes. Graphical Bayesian Belief Networks and related approaches (hierarchical models, ‘hybrid’ mechanistic/data-driven models) can be particularly powerful decision support tools that make it relatively easy for stakeholders to engage in the model building process and inform adaptive water quality management within an uncertainty framework. The aim of this session is to review the state-of-the-art in this field and compare software and procedural choices to consolidate and set new directions for the emerging community of Bayesian water quality modellers. Building on past three years’ success of this session, a specific new emphasize for this year’s session is to explore the utility of Bayesian water quality models in supporting decision making.

We seek contributions from water quality research that use Bayesian approaches to, for example but not exclusively:
• involve stakeholders in model development and maximise the use of expert knowledge
• integrate prior knowledge, especially problematizing the choice of Bayesian priors
• inform risk analysis and decision support using diverse data and evidence
• represent the preferences of the stakeholders in the form of value functions through elicitation, and account for the uncertainty in preferences
• produce accessible decision support tools
• model water quality in data sparse environments
• compare models with different levels of complexity and process representation
• quantify the uncertainty of model predictions (due to data, model structure and parameter uncertainty)
• address the problem of scaling (e.g. disparity of scales between processes, observations, model resolution and predictions) through hierarchical models
• quantify especially model structural error through, for example, Bayesian Model Averaging or structural error terms
• use statistical emulators to allow probabilistic predictions of complex modelled systems
• use machine-learning and data mining approaches to learn from large, possibly high-resolution data sets.

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, important sources of uncertainty 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 hydro-climatic 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 significantly reduce our ability to understand long-term hydrological variability and to improve projections and reconstructions of future and past hydrological changes upon 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.

This session focusses on hydrological response to changes in climatic forcing at multi-annual to multi-decadal timescales. Catchments are immensely complex and unique systems responding to external factors (e.g. changes in climate) on a variety of timescales due to complex interactions and feedbacks between their components. Recent evidence suggests a tendency for existing models and methods to downplay the impact of a given climatic change on streamflow with major implications for the reliability of such methods for future planning. The poor performance of models suggests they potentially misrepresent (or omit) important catchment processes, process timescales, or interactions between processes. The multitude of responses and feedbacks developing in the critical zone need to be disentangled and understood to improve our ability to make hydrological predictions under different and continuously changing climatic conditions.

We invite submissions on themes such as (but not limited to):
1. Better understanding of hydrological and/or biophysical processes related to long-timescale climate shifts potentially contributing to apparent shifts in hydrologic response;
2. Understanding and quantifying catchment multi-annual “memory”
3. Modelling studies aiming to evaluate and/or improve hydrologic simulations under historic climatic variability and change;
4. Efforts to improve the realism of runoff projections under future climate scenarios;
5. Studies that explore implications of long term-hydrologic change for water availability, risk, or environmental outcomes including interactions with human factors such as landuse changes, evolving water policy, and management intervention.

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 structural measures and demographic and socio-economic 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 multi-scale risk mitigation measures, such as natural water retention measures and private precautionary measures; changes of economic, societal and technological aspects driving flood vulnerability and damages, among others.
- Future flood risk scenarios and the role of adaptation and mitigation strategies

Hydrological extremes (floods and droughts) have major impacts on society and ecosystems and are posited to increase in frequency and severity with climate change. These events at the two ends of the hydrological spectrum 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 types of extremes that are increasingly being studied.

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

We welcome submissions that present insightful flood and/or drought research, including case studies, large-sample studies, statistical hydrology, and analysis of flood or drought non-stationarity under the effects of climate-, land cover-, and other anthropogenic changes. These might include storyline and stress testing approaches to better understand hydrological responses under changed (extreme) conditions. Studies that investigate both types of extremes are of particular interest. Submissions from early-career researchers are especially encouraged.

Large-scale hydrological research is very important in many different contexts - examples include: increase understanding of the climate system and water cycle, assessment of water resources in a changing environment, hydrological forecasting, and transboundary water resource management.

We invite contributions from across hydrological, atmospheric, and earth surface processes 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 combinations of these. They attempted to quantify water fluxes (e.g. evapotranspiration, streamflow, groundwater recharge) and water storage 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, increasing 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 estimates differ considerably due to the methodology and datasets used such that a robust assessment of global, continental and regional water balance components remains challenging.

This session is seeking for contributions focusing on:
i. past/future assessment of water balance components (fluxes and storages) such as precipitation, freshwater fluxes 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.

Groundwater provides about 40% of all human water abstractions and is an essential water source for freshwater biota in rivers, lakes, and wetlands. Aquifers may span political and natural boundaries, but our large-scale understanding of groundwater processes and their interconnection to surface water is still limited.
Increasingly global-scale groundwater models are being developed, and big-data assessments of groundwater wells have been conducted to push the boundaries of our large-scale understanding of groundwater processes. Similar to the catchment scale, knowledge of the exchange between surface and subsurface waters is essential for determining the hydrological water balance at larger scales. Furthermore, surface and subsurface waters exchanges, as well as inter-catchment groundwater flow, affect water, pollutant and nutrient fluxes, bio-organisms in streams, and the groundwater itself. Additionally, human activities (e.g., pumping/irrigation) could alter the natural conditions for the groundwater flow processes and exchange between surface and subsurface.
In this session, we want to highlight the increasing interest in the large-scale study of groundwater availability and processes while discussing current obstacles related to data availability and model design. Therefore, we seek contributions addressing issues including:
• Regional to global groundwater-related datasets and big-data assessments
• Transboundary and inter-catchment assessments of groundwater processes
• Surface-subsurface water exchange at the catchment to global scales from both observational and modeling aspects
• Effects of surface-subsurface water exchange on hydrological extremes (drought/flood), water availability, and solute and pollutant transport under climate change
• Implications of large-scale groundwater understanding on monitoring design and integrated water management beyond the catchment scale
• Variation of controls on groundwater processes across large domains

Hydroinformatics has emerged over the last decades to become a recognised and established field. It is concerned with the development and hydrological application of mathematical modelling, ICT, systems science and computational intelligence tools. We also have to face the challenges of Big Data: large data sets, both in size and complexity.

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. The main topics will address the following classes of methods and technologies:

* Methods for the analysis of complex data sets, including remote sensing and crowdsourced data
* Clustering algorithms: hard vs fuzzy clustering, comparison of methods, alternative clustering methods (sequential, evolutionary, deep, ensemble, etc.)
* Predictive and analytical models based on the methods of statistics, computational intelligence, machine learning and data science: neural networks, deep learning techniques, fuzzy systems, genetic programming, chaos theory, etc.
* Specific concepts and methods of Big Data and Data Science
* Optimisation methods associated with heuristic search procedures: various types of genetic and 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
* Demonstrating the benefit of the use of Citizen Observatories, crowdsourcing, and innovative sensing techniques for monitoring, modelling, and management of water resources
* Software architectures for integrating 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.

Many environmental and hydrological problems are spatial or temporal, or both in nature. Spatio-temporal analysis allows identifying and explaining large-scale anomalies which are useful for understanding hydrological characteristics and subsequently predicting hydrological events. Temporal information is sometimes limited; spatial information, on the other hand has increased in recent years due technological advances including the availability of remote sensing data. This development has motivated new research efforts to include data in model representation and analysis.

Statistics are in wide use in hydrology for example to estimate design events, forecast the risk and hazard of flood events, detect spatial or temporal clusters, model non-stationarity and changes and many more. Statistics are useful in the case when only few data are available but information for very rare events (extremes) or long time periods are needed. They are also helpful to detect changes and inconsistencies in the data and give a reliable statement on the significance. Moreover, temporal and spatial changes often lead to the violation of stationarity, a key assumption of many standard statistical approaches. This makes hydrological statistics interesting and challenging for so many researchers.

Geostatistics is the discipline that investigates the statistics of spatially extended variables. Spatio-temporal analysis is at the forefront of geostatistical research these days, and its impact is expected to increase in the future. This trend will be driven by increasing needs to advance risk assessment and management strategies for extreme events such as floods and droughts, and to support both short and long-term water management planning. Current trends and variability of hydrological extremes call for spatio-temporal and/or geostatistical analysis to assess, predict, and manage water related and/or interlinked hazards.

The aim of this session is to provide a platform and an opportunity to demonstrate and discuss innovative applications and methodologies of spatio-temporal analysis in a hydrological (hydrometeorological) context. The session is targeted at both hydrologists and statisticians interested in the spatial and temporal analysis of hydrological events, extremes, and related hazards, and it aims to provide a forum for researchers from a variety of fields to effectively communicate their research.

Machine learning (ML) and Deep Learning (DL) have seen accelerated adoption across Hydrology and the broader Earth Sciences. This session highlights the continued integration of ML, and its many variants, including DL, into traditional and emerging hydrology-related workflows. Abstracts are solicited related to novel theory development, novel methodology, or practical applications of ML 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, e.g., under non-stationarity.
(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

Proper characterization of uncertainty remains a major research and operational challenge in Environmental Sciences, and is inherent to many aspects of modelling impacting model structure development; parameter estimation; an adequate representation of the data (inputs data and data used to evaluate the models); initial and boundary conditions; and hypothesis testing. To address this challenge, methods for a) uncertainty analysis (UA) that seek to identify, quantify and reduce the different sources of uncertainty, as well as propagating them through a system/model, and b) the closely-related methods for sensitivity analysis (SA) that evaluate the role and significance of uncertain factors (in the functioning of systems/models), have proved to be very helpful.

This session invites contributions that discuss advances, both in theory and/or application, in methods for SA/UA applicable to all Earth and Environmental Systems Models (EESMs), which embraces 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) Analyses of over-parameterised models enabled by AI/ML techniques
3) Single- versus multi-criteria SA/UA
4) Novel approaches for parameter estimation, data inversion and data assimilation
5) Novel methods for spatial and temporal evaluation/analysis of models
6) The role of information and error on SA/UA (e.g., input/output data error, model structure error, parametric error, regionalization error in environments with no data etc.)
7) The role of SA in evaluating model consistency and reliability
8) Novel approaches and benchmarking efforts for parameter estimation
9) Improving the computational efficiency of SA/UA (efficient sampling, surrogate modelling, parallel computing, model pre-emption, model ensembles, etc.)

To provide support for resource management decision making, computational modeling workflows in hydrosystem simulation need to be efficient, reproducible, and robust with regard to the risk of unwanted outcomes. Unfortunately, each of these three attributes is difficult to achieve in practice; aspirations to simultaneously achieve all of them are truly lofty. Too often, modeling analyses are inefficient, the workflow is largely opaque and unknown, and the important simulated outcomes lack the context of uncertainty and/or risk.

This session calls for submissions that demonstrate rapid, reproducible and/or robust modeling through worked examples and software tools (a preference for open source). The worked examples should demonstrate how the researcher aspired to be rapid, reproducible, and robust; we are interested in the process and approach as much as the results. We aim to stimulate discussion based on lessons learned and results presented, for other researchers and practitioners to build on. We particularly welcome descriptions of trials and tribulations: What was difficult? What didn’t work? How were these issues overcome?

Software tools may include:
• techniques to automate modeling workflow elements or increase efficiency, reproducibility, robustness of decision-support modeling elements.
• frameworks to build models from original data in flexible ways that may enable hypothesis testing in the form of changing discretization, process representation, and other modeling decisions.
• multi-model frameworks such as Bayesian-model selection/combination, as well as frameworks to accommodate model structural error.
• Methods for uncertainty analysis, data assimilation, and management optimization under uncertainty in the decision-support context.
• machine-learning approaches for decision support analyses.

Flash floods triggered by heavy precipitation in small- to medium-sized catchments often cause catastrophic damages, which are largely explained by the very short response times and high specific peak discharge. Often, they are also associated with geomorphic processes such as erosion, sediment transport, debris flows and shallow landslides. The anticipation of such events is crucial for efficient crisis management. However, their predictability is still affected by large uncertainties, due to the fast evolution of triggering rainfall events, the lack of appropriate observations, the high variability and non-linearity in the physical processes, the high variability of societal exposure, and the complexity of societal vulnerability.
This session aims to illustrate current advances in monitoring, modeling, and short-range forecasting of flash floods and associated geomorphic processes, including their societal impacts.
Contributions related to the floods that occured in July 2021 in Germany and Western Europe, and in October 2020 in France and Italy (Alex storm) are particularly encouraged this year.
Contributions on the following scientific themes are specifically expected:
- Monitoring and nowcasting of heavy precipitation events based on radar and remote sensing (satellite, lightning, etc.) to complement rain gauge networks;
- Short-range (0-6h) heavy precipitation forecasting based on NWP models, with a focus on seamless forecasting strategies and ensemble strategies for the representation of uncertainties;
- Understanding and modeling of flash floods and associated geomorphic processes at appropriate space-time scales;
- Development of integrated hydro-meteorological forecasting chains and new modeling approaches for predicting flash floods and/or rainfall-induced geomorphic hazards in gauged and ungauged basins;
- New direct and indirect (proxy data) observation techniques and strategies for the observation or monitoring of hydrological reactions and geomorphic processes, and the validation of forecasting approaches;
- Development of impact-based modeling and forecasting approaches, including inundation mapping and/or specific impacts modeling approaches for the representation of societal vulnerability.

Drought and water scarcity are important issues in many regions of the Earth. While the projected 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. Drought Monitoring and Forecasting are recognized as one of three pillars of effective drought management, and 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 integrating these with the needs and knowledge of 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 drought risk management, also including drought and water scarcity interrelationship, hydrological impacts, and 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.

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.

This interactive session aims to bridge the gap between science and practice in operational forecasting for different climate and water-related natural hazards including their dynamics and interdependencies. 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. Increasingly, humanitarian, disaster risk management and climate adaptation practitioners are using forecasts and warning information to enable anticipatory/ early action that saves lives and livelihoods. It is important to understand their needs, their decision-making process and facilitate their involvement in forecasting and warning design and implementation (co-development).

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 hazards including climate emergency. Real-world case studies of system implementations - configured at local, regional, national, continental and global scales - will be presented, including trans-boundary issues. An operational warning system can include, for example, monitoring of data, analysing data, making and visualizing forecasts, giving warning signals and suggesting early action and response measures.

Contributions are welcome from both scientists and practitioners who are involved in developing and using operational forecasting and/or management systems for climate and water-related hazards, such as flood, drought, tsunami, landslide, hurricane, hydropower, pollution etc. We also welcome contributions from early career practitioners and scientists.

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.

Many water sectors are already having to cope with extreme weather events, climate variability and change. In this context, predictions on sub-seasonal and seasonal to decadal timescales (i.e. horizons ranging from months to a decade) are an essential part of hydrological forecasting. By providing science-based and user-specific information on potential impacts of variations in water availability, operational hydro-meteorological and climate services are invaluable to a range of water sectors such as water resources management, drinking water supply, transport, energy production, agriculture, disaster risk reduction, forestry, health, insurance, tourism and infrastructure.

This session aims to cover the research and operational advances in climate and hydro-meteorological forecasting, and their implications on predicting water availability for servicing water sectors. It welcomes, without being restricted to, presentations on:
- Technical challenges in making use of climate data for hydrological modelling (e.g. downscaling, bias correction, temporal disaggregation, spatial interpolation),
- Lessons learnt from forecasting and managing present day extreme conditions,
- Improved representations of hydrological extremes in a future climate,
- Seamless forecasting, including downscaling and statistical post- and pre-processing,
- Propagation of uncertainty through the forecasting chain for impact assessment and decision-making,
- Operational hydro-meteorological forecasting systems, hydro-climate services, and tools,
- Effective methods to link stakeholder interests and scientific expertise (e.g. service co-generation).

The session will bring together research scientists and operational managers in the fields of hydrology, meteorology and climate, with the aim of sharing experiences and initiating discussions on this momentous topic. We encourage presentations that utilise the WWRP/WCRP subseasonal-to-seasonal (S2S) prediction project database, and all hydrological relevant applications.

The occurrences of extreme flood events have increased globally in the last two decades as noted by recent rare and catastrophic flooding events in Germany, Belgium, China, the USA and in the monsoon season of India. Advanced innovative methods and conceptual improvements in existing approaches are required to address the modelling and management of the spatial and temporal complexity of extreme floods. The observed increase in frequency and severity of events can be predicted by joint probabilistic analyses of precipitation and river flow extremes. Evidence from the rare extreme events indicates that assumptions of Holocene climate stationarity is not applicable anymore for hydrologic analysis and design. The observed significant changes in weather patterns and characteristics that lead to extreme precipitation in different parts of the world far exceeded the design capacities of local protection infrastructures and systems – resulting in massive flooding, casualties, and economic losses. The watershed response to the extreme precipitation is the worst when combined with saturated steep catchments combined with antecedent moisture conditions. Prediction of region-scale and localized extreme events well ahead of time is a real challenge. New design protocols have required that account for uncertainties in future meteorological events and provide flexibility in the design and operation of infrastructure to minimize the consequences of extreme events. Understanding the mechanisms of extreme precipitation and its hydro meteorological connection with flooding, especially under the circumstances of global climate change, is critical for flood prevention and mitigation. This session invites research papers that focus on scientific and technological developments in extreme precipitation estimation, flood monitoring, and flood modelling, with the end goal of improving flood prevention and mitigation. The research studies discussing advancements in situ measurement and remote sensing of extreme precipitation, rainfall-runoff modelling, statistical and hydrological analysis of extreme precipitation and flood, flood forecasting and warning, and impact assessment of climate change and land use/cover change on flood are also invited. Research works that emphasize and discuss case studies on modelling extreme events are also expected to gain and learn from insights gained from flood disaster modelling and management.

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/or 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.

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 hydropower systems, 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 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 that explore the use of hydropower and storage technologies to support the transition to low-carbon electricity systems. We specifically encourage interdisciplinary teams of hydrologists, meteorologists, power system engineers, and economists to present on case studies and discuss collaboration with environmental and energy policymakers.
Questions of interest include:
- Prediction of water availability and storage capabilities for hydropower production
- Prediction and quantification of the space-time dependences and the positive/negative feedbacks between wind/solar energies, water cycle and hydropower
- Energy, land use and water supply interactions during transitions
- Policy requirements or climate strategies needed to manage and mitigate risks in the transition
- Energy production impacts on ecosystems such as hydropeaking effects on natural flow regimes.

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 frameworks that help design and test efficient and sustainable water management strategies to meet the water challenges of the 21st century. System-scale analyses adopt practical, problem-oriented approaches for addressing the most challenging water issues of our times. These include competing objectives for water, multi-stakeholder planning and negotiation processes, multi-sector linkages, and dynamic adaptation under uncertainty. The session will feature state-of-the-art contributions to system-scale water management solutions for an uncertain environment.

Highly varying hydro-climatological conditions, multi-party decision-making contexts, and the dynamic interconnection between water and other critical infrastructures create a wealth of challenges and opportunities for water resources planning and management. For example, reservoir operators must account for a number of time-varying drivers, such as the downstream users’ demands, short- and long-term water availability, electricity prices, and the share of power supplied by wind and solar technologies. In this context, adaptive and robust management solutions are paramount to the reliability and resilience of water resources systems. To this purpose, emerging work is focusing on the development of models and algorithms that adapt short-term decisions to newly available information, often issued in the form of weather or streamflow forecasts, or extracted from observational data collected via pervasive sensor networks, remote sensing, cyberinfrastructure, or crowdsourcing.

In this session, we solicit novel contributions related to improved multi-sectoral forecasts (e.g., water availability and demand, energy and crop prices), novel data analytics and machine learning tools for processing observational data, and real-time control solutions taking advantage of this new information. Examples include: 1) approaches for incorporating additional information within control problems; 2) methods for characterizing the effect of forecast uncertainty on the decision-making process; 3) integration of information with users’ preferences, behavioral uncertainty, and institutional setting; 4) studies on the scalability and robustness of optimal control algorithms. We welcome real-world examples on the successful application of these methods into decision-making practice.

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.

Land use and land cover (LULC) changes are one of the main drivers of changes to hydrological processes, altering the ecosystem dynamics and impacting the production of water-related ecosystem services (e.g. water provision, flood regulation, …) with different levels of societal impact.
LULC changes can be determined by anthropic and/or natural drivers and can affect many hydrological processes, including rainfall interception, evapotranspiration, moisture recycling, runoff generation, erosion, groundwater recharge, pollution and alteration of surface and groundwater quality. Such effects may in turn affect water-related ecosystem services and have an impact on the possible water-land nexus scenarios which should be understood, to inform effective and equitable water resources management.

This 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 change impacts on all water resources management (blue, green, atmospheric) and water-related ecosystem services
• Assessments on the impact and extent of multi-level policies that drive LULC changes, as well as studies at the science-policy interface on the water-land nexus
• Advances in (interdisciplinary) methodologies for identifying water-related ecosystem services (WES), as well as studies highlighting spatial assessments of WES

Keynote Speaker: Wouter Buytaert, Professor in Hydrology and Water Resources at the Imperial College London - https://www.imperial.ac.uk/people/w.buytaert

For the improvement of water quality both the restoration of wetlands but also the establishment of different filter solutions such as constructed wetlands, bioreactors, integrated bufferzones and saturated bufferzones as drainage mitigation measures are important strategies applied for combating sediment and nutrient losses to surface waters as part of Water Framework Directive, River Basin Management Plans. It is essential to know the processes and driving factors behind that control sediment and nutrient retention and their relative importance over time to ensure the best management. Moreover, there is also a great need to learn about possible side-effects to avoid inter alia nutrient swapping. Perfect knowledge of the processes, namely their large spatial and temporal variability may never be achieved. Still, it is essential that we communicate what is known to water authorities and landscape managers to foster environmentally sound decision making. Additionally, other aspects, such as economic and social issues may vary greatly, even on a local scale, consequently such measures must be implemented as one element within a holistic and systemic management plan.
This session deals with various nature based and filter-based solutions to reduce the losses of sediment and nutrients from agriculture. The session looks for new advancements in already established measures, such as restoration of riparian wetlands, larger lowlands areas including fens and swamps, re-establishment of shallow lakes, constructed wetlands (surface flow and subsurface flow), as well as drainage mitigation measures recently introduced in Europe and still under development such as integrated buffer zones, saturated buffer zones and controlled drainage.

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.

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 transformation of urban water infrastructure and the adoption of digital solutions for water resources are opening new opportunities for the design, planning, and management of more sustainable and resilient urban water networks and human-water systems across urban scales. The “digital water” revolution is strengthening at the same time the interconnection between urban water systems (e.g., drinking water, wastewater, urban drainage) and other critical infrastructures (e.g., energy grids, transportation networks). This interconnection motivates 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, frameworks, and methodologies for planning and management of modern urban water infrastructure, with a particular focus on digitalization and/or interconnections 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, asset management, decision making, novel applications of IoT, 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, artificial intelligence for water applications, descriptive and predictive models of water demand, experimental approaches to demand management, water demand and supply optimization, or the identification of trends and anomalies in hydraulic sensor data (e.g., for leak detection). Interesting investigations on interconnected systems can include, for example, cyber-physical security of urban water systems (i.e., communication infrastructure), combined reliability and assessment studies on urban metabolism, or minimization of flood impacts on urban networks.

The need for improved, continuous, and sustainable provision of water supply and wastewater services has exerted mounting pressures on water and wastewater supply (WWS) systems, administered by the public, private, and public-private utilities. Many of the WWS systems are currently facing major challenges like aging infrastructure, network losses, and high energy consumption, which dramatically increase operational and maintenance (O&M) costs and threaten the uninterrupted provision of services. Climate change will create additional risks to WWS systems that will need to be addressed.

To overcome the operational challenges, WWS systems are introducing novel technical approaches to improve performance and also minimize environmental impacts to the linked water sources. There are also attempts to measure and improve the technical and financial capability of WWS utilities, so that O&M costs can be covered and the system’s performance, in the long run, can be safeguarded. This may lead to tariff increases, and hence the economic impacts faced by poor households and disadvantaged groups with respect to the payment of WWS services are also explored. Although the cost of water supply and sanitation services are relatively low as compared to average household incomes, concerns have arisen on the affordability for the poorest segments of the population.

In this session, we invite contributions to different technical and socio-economic approaches and indicators that can improve the sustainability challenges of urban water systems. We are interested in original and review studies, focusing on the inter-disciplinary conceptualization of WWS and sustainability challenges by including different dimensions such as hydrology, socioeconomics, management, finance, and environment.

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.

The socio-economic impacts associated with floods are increasing. 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, while the overall economic damage is estimated to be more than $300 billion. Despite this evidence, 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, as well as many datasets from airborne sensors carried on airplanes and drones. 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 as well as airborne sensors (aircraft and drones);

- 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.)

This session concerns measurements and estimations of water levels, water extent, water storage and water discharge of water bodies such as rivers, lakes, floodplains and wetlands, and groundwater, through combined use of remote sensing and in situ measurements. Contributions that also cover aspects of assimilation of remote sensing and 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 contribute by providing near real time measurements and 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 spaceborne techniques. Interferometric Synthetic Aperture Radar (InSAR) is also commonly used to understand wetland connectivity, 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, Sentinel-3A/B and Sentinel-6 missions are maturing, including the Fully-Focused SAR technique offering very-high resolution. The future SWOT mission will open up many new hydrology-related opportunities. Preparation studies results for Sentinel-3 Next Generation and CRISTAL are encouraged.

Snow constitutes a freshwater resource for over a billion of people world-wide. High percentage of this water resource 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 to water supply but also ecosystem over these areas. Therefore, understanding seasonal snow dynamics, possible changes and implication have become crucial for water resources management. Remote sensing has proven to be the main technique used to monitor the snow properties across mid-large extensions and their hydrological implications, for decades now. Moreover, the recent advances, which are focused on the study of snow properties at higher spatio-temporal scales (e.g., small-scale snow-topography interactions, snow-vegetation interaction, diurnal variation of snow, rain over snow events), are helping to understand better snow acumulation, distribution and ablation dynamics.
This session is focused on studies linking the use of remote sensing of seasonal snow in hydrological applications: 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.

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 will focus on: the use of remote sensing data to estimate irrigation volumes and timing; 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.

A thorough understanding and assessment of evapotranspiration (ET) is integral to short- and long-term management decisions in agricultural, riparian, urban greenery, and forest lands. Recent advancements in remote sensing (RS), accessibility to free satellite imagery (e.g. MODIS, Landsat, Sentinel), availability of advanced platforms like Google Earth Engine (GEE), and application of the latest techniques of Artificial Intelligence (AI) have contributed to a more accurate estimation of ET at different spatial scales in various climates and eco-geographical regions for a range of green landcovers. Increasing the accessibility and resolution of RS data enables upscaling, routine updating and consistent measurements of physical properties, which would be difficult or costly to obtain from the ground. However, there is still a lot to discuss and debate about advances in development, localizing, validation and calibration of available methods, and reducing sources and magnitudes of uncertainties and biases.

At the RS-ET session, we welcome studies that estimate ET using RS-based data streams. The scope of the session will include: (1) advances in remote sensing-based ET estimation, (2) time-series and upscaling applications for a range of landcovers and spatiotemporal scales, (3) localizing available methods and their challenges, (4) validation and calibration and (5) accuracy assessment and enhancement.

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.

Remote sensing products have a high potential to contribute to monitoring and modelling of water resources. Nevertheless, their use by water managers is still limited due to lack of quality, resolution, thrust, accessibility, or experience.
In this session, we look for new developments that support the use of remote sensing data for water management applications from local to global scales. We are looking for research to increase the quality of remote sensing products, such as higher resolution mapping of land use and/or agricultural practices or improved assessments of river discharge, lake and reservoir volumes and groundwater resources. We are interested in quality assessment of remote sensing products through uncertainty analysis or evaluations using alternative sources of data. We also welcome contributions using a combination of different techniques (physically based models or artificial intelligence or techniques) or a combination of different sources of data (remote sensing and in situ). Finally, we wish to attract presentations on developments of user-friendly platforms providing smooth access to remote sensing data for water applications.
We are particularly interested in applications of remote sensing to estimate the human water interactions such as dam operations and/or irrigations.

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.

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.

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. 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.
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 accuracy in precipitation time series due to, e.g., 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 approaches to modelling of precipitation 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.

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.

Hydroclimatic conditions and availability of water resources in space and time constitute important factors for maintaining adequate food supply, the quality of the environment, and the welfare of citizens and inhabitants, in the context of a post-pandemic sustainable growth and economic development. This session is designed to explore the impacts of hydroclimatic variability, climate change, and temporal and spatial availability of water resources on different factors, such as food production, population health, environment quality, and local ecosystem welfare.
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.
• Smart infrastructure for water usage, reduction of water losses, 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 supply, 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 forcing (e.g. inappropriate agricultural practices, and land usage) on the natural environment (e.g. health impacts from water and air, fragmentation of habitats, etc.)

Water resources managers and scientists are facing several challenges when applying climate models for hydrological variables. Indeed, a gap exists between what is provided by climate scenarios and what is needed and useful for water resources managers. In order to reduce this gap and enhance the assessment of climate change impacts, we need to improve our understanding, knowledge and model representations of the interactions between climate drivers and hydrological processes at the regional scale. This is essential to outline forecasts and assess extreme events risk, where uncertainty, probabilistic approaches ad prediction scenarios should be properly defined.
This session particularly welcomes, but is not limited to, contributions on:
- Advanced techniques to simulate and predict hydrological processes and water resources, with emphasis on stochastic and hybrid methods.
- Advanced techniques to simulate and predict hydroclimatic extreme events including compound extreme events relevant to water resources management (e.g. heatwaves and droughts).
- Holistic approaches to generate future water resources scenarios integrating also anthropogenic and environmental perspectives.
- Hydroclimatic change attribution studies using probabilistic approaches and novel causality frameworks with uncertainty assessment.
- Evaluation of climate models performance at the regional scale using observational data
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 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, warning systems, and rapid damage assessment.
- 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 responses. 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.

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 spatially compounding 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 spatially compounding events at different spatial scales.

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.

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.

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 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).

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 their temporal dynamics at which they impact the natural environment. A wide range of innovative methods have recently emerged that provide vision into the coupled processes at spatial and temporal scales unexplored before, including: 4D geophysical methods, near-real time biochemical and isotopic monitoring, smart sensors and observation systems, remote sensing, citizen science observations, microscopic imaging technics, pore to global scale numerical models, data-driven machine learning and hybrid modeling approaches.
The session seeks contributions that present (i) technological innovations in experimental and sensing methods for the observation of physical and biochemical processes occurring in the subsurface; (ii) advances in computational methods that help extracting knowledge from datasets integrating time, space and scientific disciplines; and, (iii) improvements of modeling technics for the description of coupled physical and biochemical processes from the micro to the kilometer scales. Reviews and general discussions on current technological and observation challenges are also highly encouraged.

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.

This session deals with the use of geophysical methods for the characterization 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 are the need for improved quantitative use of geophysical measurements in model conceptualization and parameterization, 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.

Climate change is 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 globally. Despite the important potential role of groundwater storage in climate change adaptation strategies, this role and the actual impact of climate change on groundwater resources remain highly uncertain. The pathways through which changes in natural (e.g., evaporation, transpiration and rainfall) and human factors (e.g., groundwater abstractions, water management strategies) impact groundwater resources are only partially understood due to the complexity and the many (unknown) feedback mechanisms of the atmosphere-land-subsurface system, including humans as an agent. Therefore, this session focuses on: How are different groundwater-related 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? How to design and assess potential (ground)water management strategies to increase resilience?
We are inviting presentations taking up these challenges and with a particular interest in process-based analysis and models. We especially encourage (but do not limit to) contributions on the following topics:

Impact of climate change:
- on groundwater recharge (e.g. through changes in rainfall, evaporation, transpiration, etc.).
- on salinity and water availability in coastal aquifers due to sea-level changes and dilution.
- on groundwater extremes (both droughts and high groundwater levels).
- on changes in dilution potential or leaching potential for contaminants, including pesticides and nutrients.
Human impacts on and management of groundwater resources under a changing climate:
- Impacts of groundwater abstractions, land-use changes, river regulation
- Groundwater-surface water management strategies
Feedback between groundwater and climate through coupled models:
- Methodologies 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.

The proper management of blue and green water is vital for sustainable livelihoods in drylands (i.e. hyper—arid, arid, semi—arid and dry sub—humid lands), where any productive activity is structurally and deeply related to the understanding of soil hydrological behaviour. In these areas groundwater is usually the primary source for drinking water supply and irrigation so that water management is critical to the water-food-energy security nexus.
Irrigation, in particular, should be regarded as a fundamental element of any agroecosystem and an effective defence against desertification. This as a consequence of the fact that on one hand traditional irrigation is often a cultural heritage, which requires to be faced with an interdisciplinary approach, while on the other hand incorrect irrigation techniques may lead to soil and groundwater salinization, with dramatic fallout on agricultural productivity.
Also, due to local shifts in climate and in the hydrological cycle, or global changes such as population growth and changes in land use, drylands and regions with high water stress are expected to expand globally: for example, catchments in Central Europe with continental climate and decreasing precipitation in summer periods are likely to be new areas subjected to water stress.

This session welcomes contributions ranging from the understanding of the soil hydrological behaviour and of the mass fluxes through the soil in drylands and environments under stress conditions to the identification of the consequences of a changing environment for better future management, protection, and sustainable use of water resources in drylands.
This includes adapted modelling techniques coupling climate models with hydrological models or with soil water and groundwater models, or studies dealing with groundwater quantity and quality, the interaction between irrigation and soil hydrology, and the design of irrigation systems in arid districts and oases, also involving non—conventional waters (e.g. water harvesting). Particular attention will be given to traditional irrigation techniques as well as to precision irrigation techniques, also with local community involvement.

Due to a frequently associated data scarcity issue in dry regions, methodologies and strategies addressing uncertainty and limited data availability are of interest for this session. Interdisciplinary contributions and contributions from appropriate field observational studies are encouraged as well.

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 over-exploitation, conflicts in use, climate change, resource development or contamination). Papers related to methods of characterizing groundwater flow systems, and preventing, controlling and mitigating harmful environmental impacts related to groundwater, including those in developing countries, are also welcome.

Karst environments are characterized by distinctive landforms and unique hydrological behaviors. Karst systems are 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, and are extremely variable in time and space. Furthermore, karst systems are highly vulnerable to a variety of hazards, due to the direct connection between the surface and subsurface through the complex networks of conduits and caves.
In karst, any interference is likely to have irreversible impacts and disturb the natural balance of the elements and processes. 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 transmission through conduit flow, and remediation action, when possible, could be very expensive and require a long time; 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 from karst areas worldwide related to geomorphology, hydrogeology, engineering geology, hazard mitigation in karst environments in the context of climate change and increasing human disturbance.

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.

Pressure in water resources is increasing rapidly as a result of climate change and the growing population. In this context, urban groundwater plays an essential role as a strategic resource for the development of cities and must be preserved. However, a wide variety of human/urban related activities modify the physico-chemical conditions of urban aquifers, among others:
• The release of chemicals from sources such as wastewater (throught direct discharges or leaky sewers) and urban runoff
• The introduction of contaminants of emerging concern such as pharmaceuticals, personal care products, illicit drugs…
• The introduction of industrial compounds such as chlorinated solvents, perfluorinated compounds,…
• The interaction with underground constructions
• The alteration of baseflow and surface water quality
• The modification of transit times
• The use of shallow aquifers for geothermal energy
• The increase of urbanized areas and sealed surfaces
• The alteration of the fresh-salt water interface in coastal aquifers (i.e., saltwater intrusion)
Accordingly, it is of paramount importance to assess qualitatively and quantitatively the aspects that may alter the physico-chemical conditions of urban aquifers and develop methods for preserving them.
This session welcomes contributions (laboratory and pilot-scale experiments, case studies, numerical investigations, etc) focused on urban groundwater resources.

During the last decades we have seen an exponential increase in new anthropogenic chemicals such as pharmaceuticals, personal care and household products, industrial or agricultural chemicals etc. Some of these of chemicals are potentially harmful and persistent in the environment and they are increasingly being detected at low levels in surface- and groundwater. Many such emerging contaminants (e.g. PFASs, pharmaceuticals, pesticides, nanoparticles etc) may demonstrate low acute toxicity, but can still produce long-term adverse health effects even at very low levels of exposure. These chemicals have produced many additional challenges for groundwater management, risk assessment and remediation. Questions related to the mobility, persistence and potential transformation or degradation of emerging contaminants in both the saturated and unsaturated zones have to be addressed. Additional challenges may include interactions or competition between different chemicals and/or natural constituents such as colloids and organic matter, cocktail effects and the capability of existing models, developed for traditional contaminants, to make reliable predictions of ultra-low concentrations. The questions of how best to physically and chemically characterize sites contaminated by this class of contaminants also have to be visited. For traditional contaminants challenges may also remain to meet cleanup goals due to a multiplicity of factors that include geologic heterogeneity, unknown sources, and knowledge gaps in the understanding of complex reactive processes, specifically with chemical mixtures.

This session seeks papers on process understanding through laboratory and field research, modeling, and site characterization to address new challenges and solutions associated with groundwater contamination from emerging contaminants as well as unsolved challenges related to traditional contaminants.

Groundwater salinization in the Mediterranean is a phenomenon of increasing relevance and a focus area of subsurface water quality studies. Still, several recent reviews of the topic have identified that there still is a lack of studies addressing the temporal variations and spatial variations in groundwater and salinization in coastal aquifers in three dimensions. The session aims at exploring the dynamics of groundwater salinization. We invite contributions addressing temporal variations at all time scales and spatial or even combined spatial-temporal dynamics. Experimental data, projections, and reconstructions are needed showing variations of salinization at different time scales, from seasonal to historical and paleo-hydrological, e.g., by using residence time analysis combined with salinization indicators or modeling techniques. Hopefully, examples of receding salinization trends due to remediation or management actions can also be presented to show the dynamics of reverted salinization. We welcome high-resolution or long-time series of groundwater salinization related to tidal effects, pumping, or changing external driving forces that provide a better understanding of the dynamics of salinization. There is also an interest in spatial dynamics of the extent and development of transition zones between salt and fresh water. Contributions with various methodological approaches such as geophysics, geochemistry, environmental isotopes, remote sensing, multi-parameter monitoring, and combined approaches will be considered.
We aim at synthesizing and fostering a better understanding of common principles in the dynamics of the progression or recession of groundwater salinization.

Data-driven models are increasingly used to solve groundwater problems. These types of models require less knowledge about the subsurface and depend more on the input and output data. The focus is typically on groundwater level time series, with the goal to obtain as much information as possible from these measurements. Models can, for example, be used to predict future groundwater levels, determine the effect of a pumping station, or analyze data to support more traditional groundwater modeling methods. In this session, we seek contributions on the development of new and improved data-driven methods to model groundwater level time series, as well as applications and comparative studies of existing methods to solve groundwater problems. Data-driven models include, but are not limited to, time series models, machine learning models, and conceptual 1D groundwater models. Contributions are also sought on typical challenges that arise when modeling groundwater time series, such as non-stationary time series, irregular time steps, and regionalization of model results to the scale of an aquifer.

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 characterization of unsaturated flow is important e.g. for understanding the impact of climate change on water availability and groundwater resources, or the effects of droughts on ecosystem functions and agricultural productivity. Moreover, an adequate description of water flow in the unsaturated zone is required for evaluating the fate of pollutants in the earth critical zone to minimize possible threats to groundwater resources. Water flow characterization is often challenging due to subsurface heterogeneity, strong non-linearity within and between processes and the contribution of preferential flow paths. The latter may result from macro-pore networks (such as fractures, plant root or earth worm channels), so that water and pollutants can bypass most of the matrix and thus enable a fast water flow and contaminant transport in unsaturated zone. This session aims at illustrating and discussing current research of flow processes within the unsaturated zone, including field studies and experiments as well as modeling approaches and simulation studies. More specifically, we encourage researchers to participate with contributions among the following topics:
-) Monitoring of flow and transport in the unsaturated zone, from field and lysimeter studies to pore scale observations
-) Measuring and modeling of environmental tracers, including stable water isotopes, for characterizing subsurface flow processes at different spatial and temporal scales
-) Geophysical investigations for determining structures and mechanisms that can induce preferential flow and transport in different dimensions
-) Identification and quantification of water and solute transport processes, especially in the context of changing climate conditions that alter bio-geochemical processes
-) Investigating the influence of plant growth on preferential flow and transport (e.g. investigation of root water uptake dynamics or evapotranspiration patterns)
-) Development of new modeling approaches for describing unsaturated flow and reactive transport, given a restricted availability of field measurements and observations; e.g. in the context of tools for decision support
-) Sensitivity and uncertainty analyses related to the characterization of subsurface flow and both conservative and reactive transport

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 techniques 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

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 erosion, transport, and deposition of sediment by hydrodynamic mechanisms, are key features for various research disciplines, e.g., geomorphology and paleoclimatology or hydraulics, river engineering and water resources management and hydrology. Accurate quantification of erosion, transport, and deposition rates, conditioning river channel morphology, and bed composition, is fundamental for adequate development of conceptual sediment budget models and for the calibration and validation of the 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 in determining sedimentary and hydro-morphological processes in rivers, lakes, and reservoirs, estuaries as well as in coastal and maritime environments. It focuses on the quantification of bedload and suspended load, bedforms migration, channel horizontal migration, bed armoring and colmation, but also the transport mode, flocculation, settling, and re-suspension of the sediment particles.
Contributions are welcome with a particular focus on single and combined measurement techniques, post-processing methods as well as on innovative and advanced monitoring concepts for field and laboratory applications. We welcome contributions containing recent results in a temporal and spatial scale on sediment budgets as well as on sedimentary and morphodynamic processes in open water environments.
Contributions may refer but are not restricted to:
• Measurements of suspended sediment and/or bedload transport in open water environments, e.g., with classical or novel methods;
• Determination of sediment characteristics, e.g., with mechanical bed material samplers or freeze core technique;
• Innovative measurement approach or techniques aimed for validation and calibration of numerical models;
• 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 armoring, meandering
migration, river bends evolution;
• Measuring networks / multiple point datasets;
• Large- or small-scale monitoring concepts including case studies;
• In-situ or laboratory calibration of measurement data using classical or novel (e.g., machine learning) approaches;

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 armouring or density-driven transport. Hence, new generations of numerical techniques open the possibility to explore numerous outstanding research questions related to hydro-morphologic processes. Artificial Intelligence procedures offer an additional alternative to hydro-morphological studies, e.g., determining particle size or floodplain vegetation cover.
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

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, portraying 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. Contributions relative to all terrestrial and aquatic systems are welcome, including those relative to managed ecosystems, showing how human intervention alters the interactions between water and ecosystems.

This session provides a platform for interdisciplinary science addressing the continuum from the river source to the sea. A systems approach is indispensable for science-based solutions to sustainably manage complex River-Sea social-ecological systems. Studies linking environmental and social sciences and crossing geographical borders are particularly invited: from the river source and its catchment through estuaries, deltas and marshlands across the freshwater-marine water transition into the coastal sea, including surface-groundwater interaction. Studies addressing the impacts of climate change and extreme events and the impact of human activities on water and sediment quality and quantity, hydromorphology, biodiversity, ecosystem functioning and services of River-Sea continua are of particular interest.

We need to understand how River-Sea Systems function and to address many open questions. 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 social-ecological 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 balance 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.

Evapotranspiration (ET) is the key water flux at the interface of soil, vegetation and atmosphere. Methods to quantify this flux (and its individual components) have been developed within different research disciplines encompassing plant physiology, soil science, meteorology, hydrology and more. However, each method refers to a specific measurement scale and contains its own uncertainties. Bridging these scales for comparisons between the different methods – as well as remote sensing products and model outputs – requires careful consideration of the associated uncertainties and scaling assumptions.

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 (including day- and nighttime processes) 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 are thus sensitive to changes in climate and hydrological boundary conditions. The hydrology of peatlands is fundamental to their functions and development. Soil hydrological properties can change drastically after disturbances such as drainage, permafrost thaw, or mechanical compaction, 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, support of low flows 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 addresses peatlands in all latitudes, including especially permafrost and tropical peatlands for which field studies are scarce and the inclusion into Earth system models is largely pending.

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 are integral components of aquifer-river and aquifer-lake continua. Groundwater-surface water interactions result in strong bidirectional interactions between surface waters, aquifers and connecting interfaces such as hyporheic zones, benthic zones, riparian corridors and lake sediments. Current research focuses on the effects of water exchange on the transport and transformation of nutrients, microplastics and pollutants. It also addresses the control of heat, oxygen and organic matter budgets available to microorganisms and macroinvertebrates in sediments. There is still a need to better understand the links between physical, biogeochemical, and ecological process dynamics at groundwater-surface water interfaces and their implications for fluvial ecology or limnology, respectively. It is important to consider the response of exchange fluxes to environmental and climate effects at different spatial and temporal scales (e.g. river channel, alluvial aquifer, regional groundwater flow). We see the biggest and most urgent challenges of this research in upscaling and downscaling of a general conceptual framework and an improved process understanding for groundwater-surface water interfaces. We also welcome contributions that address the development and application of novel experimental methods to study the physical, biogeochemical and ecological conditions at the groundwater-surface water interface in rivers, lakes, riparian zones and wetlands. We are also looking forward to investigating the role of hyporheic processes in the retention and natural attenuation of nutrients and pollutants, particularly with regard to their impact on surface and groundwater quality. In addition to experimental work, we are interested in hydrological, biogeochemical and ecological modelling approaches (e.g. transient storage models, coupled groundwater-surface water models, etc.). Finally, we welcome the presentation of research on the impact of groundwater-surface water interactions on management and risk assessment in view of the European Water Framework Directive.

Invited speaker: Audrey H. Sawyer, The Ohio State University, School of Earth Sciences

Held annually since 2005, the session has been enjoying continuously growing interest within the EGU programme HS10 “Ecohydrology, wetlands and estuaries” . The session is focused on research of lakes, enclosed or semi-enclosed seas (Baltic Sea, North Sea, Black Sea, Caspian Sea, Aral Sea, etc.), gulfs, and lagoons. The event is intended as interdisciplinary between hydrology, limnology and oceanography. Its scope encompasses physical, chemical, and biological aspects of lakes and inland seas, and offers a forum for both observational and modelling studies.
Session content:
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.

The modern scientist has to operate in the Research-Services-Policy nexus to create real-world impact. The challenge is daunting and the opportunities are endless. What is truly the role of a scientist? What is your current position in this nexus? Where would you like to be in the future?

By sharing and discussing how our work is related to hydrological research, services and policy we can gain insight into how we, as a community, are positioned within this nexus. From there, we can identify opportunities and challenges associated with moving into new areas where we want to contribute, both personally and institutionally.

In this synergistic session, we will first use online interactive tools to explore where we, personally and as a group, fit within the Research-Services-Policy nexus. In the second part, we will have roundtable discussions on the visual outcomes of the first activity.

The objectives of this short course are to:
- create awareness of the several roles we can play as hydrologists,
connect over the challenges that come with balancing these different roles and sharing insights,
- identify topics / subjects / actors / issues and potential interlinks between hydrological research, services, and policy,
- and define a group perspective on the issues central in the proposed great debate “Hydrology and Earth System Science: research, services or policy?”

We embrace the “hybrid GA concept” by offering interactive activities using online platforms (survey, mind mapping and art tools) to promote engagement in the discussion regardless of participants’ locations and modes of attendance.
Anyone interested in the sciences, services and policy-making is encouraged to participate. A healthy mix and diversity of participants will greatly improve the experience for all involved.

This is a complementary event to the proposed Great Debate “Hydrology and Earth System Science: research, services or policy?”, and is organised in cooperation with the Young Hydrologic Society (http://younghs.com/).

On 9 August 2021, the Intergovernmental Panel on Climate Change (IPCC) released the first volume of its 6th Assessment Report (AR6). The Working Group I contribution to the Report (Climate Change 2021: The Physical Science Basis) synthesises over 14,000 publications and represents the most comprehensive and up-to-date assessment of the climate system and climate change. Crucially, the Report highlights the unprecedented and potentially irreversible influence of anthropogenic climate forcing, and for the first time, explicitly states that human influence on the climate system is unequivocal.

This short course will be a panel discussion where authors and contributors of Working Group I unpack how the IPCC 6th Assessment Report (AR6) is produced, provide personal behind-the-scenes insight on its development, and discuss its global impact, including how it is used to inform policy. Authors of the report will share their experiences of working on the report before and through the COVID pandemic. Panelists will also emphasise various ways in which scientists of all career stages can contribute to the IPCC process. Ample time will be allocated for open discussion for the audience to ask related questions to the panelists.

For more information about the AR6 please visit the IPCC website: https://www.ipcc.ch/.

One of the fundamental drivers of scientific progress is research integration and synthesis, which is essentially beneficial for developing research vision. Hence, literature reviews prove to be highly useful to many researchers at all academic stages. Analysing the literature and writing reviews for a thesis, article or project proposal can be sometimes challenging to fresh early career scientists. For a review paper even greater attention must be given to the methodological approach to conduct a reproducible and thorough review of the existing scientific literature.

In this short course participants will be given an overview of (literature) review types and learn about existing guidelines for conducting reviews. They will be introduced to available R packages for literature search and conducting systematic reviews. The course will also cover some insights from an editor’s perspective with helpful tips on how to write a review paper.

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

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 fifth 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:
• Topic tbd (Claudia Brauer)
• Identification of hydrologic events (Conrad Wasko + Danlu Guo)
• Flood forecast verification in R (Andrea Ficchi)
• The (mis)use of colours in scientific visualizations (Michael Stoelzle)
• Machine learning for spatio-temporal modelling (Razi Sheikholeslami)

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).

Visualisation of scientific data is an integral part of scientific understanding and communication. Scientists have to make decisions about the most effective way to communicate their results everyday. How do we best visualise the data to understand it ourselves? How do we best visualise our results to communicate with others? Common pitfalls can be overcrowding, overcomplicated plot types or inaccessible color schemes. Scientists may also get overwhelmed by the graphics requirements of different publishers, for presentations, posters etc. This short course is designed to help scientists improve their data visualization skills in a way that the research outputs would be more accessible within their own scientific community and reach a wider audience.
Topics discussed include:

- Choosing a plot type – keeping it simple
- Color schemes – which ones to use or not to use
- Creativity vs simplicity – finding the right balance
- Producing your figures – software and tools
- Figure files – publication ready resolutions

This course is organized by the Young Hydrologic Society (YHS), enabling networking and skill enhancement of early career researchers worldwide. Our goal is to help you make your figures more accessible by a wider audience, informative and beautiful. If you feel your graphs are complicated or not intuitive, we welcome you to join this short course.

This short course will prepare the engineer,water resource professionals and scientist to use the HEC-RAS computer program in real world situations.HEC-RAS is user friendly, computationally efficient, and runs within, and fully supports, the Microsoft Windows environment. It uses the latest graphical user interface (GUI) technology for data entry, graphics, and display of program results. Complete context-sensitive help screens are available for every program feature and option. Software includes the following functions: file management, data entry and editing, hydraulic analyses, tabulation and graphical displays of input and output data, reporting facilities, and on-line help.The participants of the course will learn how to compute water surface elevation for different river discharges for steady and unsteady flow conditions.The Geo scientist who knows River water level can compute the river discharge of that time may be thousand of years before. The unsteady flow analysis will help river engineers and participants of nay discipline to know how the flood waters may have passed a specific section. He can run the calibrated and validated model to predict water surface elevation for different scenarios of flow resulted from a river basin. This course will help to know water level of a stream passing through a small campus to large rivers with very high discharges.

We have developed an open source software package in python for ground-based GNSS reflections – gnssrefl (https://github.com/kristinemlarson/gnssrefl). This new software supports geoscientists wishing to measure in situ snow accumulation, permafrost melt, firn density, tides, and lake/river levels. We have developed videos (hosted on youtube) to help new users understand both the basic concepts of GNSS reflections and how to install and run the gnssrefl code. More than a dozen use cases are available online; Jupyter Notebooks have been developed as well. We envision the EGU tutorial session to be hands-on and interactive, with a focus on demonstrating the gnssrefl software and online tools (https://gnss-reflections.org), examining and discussing environmental results derived from GNSS data taken from public archives, and analyzing new datasets suggested by the students.

Research, especially for early career scientists (ECS), starts with the spark of an idea and is then often challenged by empirical or methodological road bumps and seemingly dead ends. In Earth Science research, we face a diverse range of challenges, including (1) access difficulties, whether for field sites, equipment or data, (2) problems of temporal and spatial scaling and extrapolation and (3) a lack of methods, theory or knowledge or (4) every day live challenges as a scientist. As part of SC4 we want to address some of those 'problems'. In the discussion of these challenges we seek to find possible solutions, suggest new research approaches and methods, and encourage further networking amongst early career scientists at future international conferences.

We will start the session at this year's hybrid meeting with 2 minute ‘pop-up’ presentations outlining some challenges. These pop-ups are followed by chaired and structured outbreak group discussions. There will be the option to join these discussions both in-person and virtually. To wrap up the session, solutions and suggestions from each group are presented to the whole session in a final discussion. This short course lives by your input, so participants are expected to actively engage to crowd solve the presented challenges. To ensure that people are able to have a safe and open space to share their ideas, we ask you to join for the whole session. You can get an idea of past crowd-solving sessions, both in-person and online, from our 2019 (EGU blog) and 2021 (EGU blog) blog posts, see links below.

If you have a 'problem' you would like to discuss in the networking session with us, please send a short statement (3-4 sentences) of your idea or challenge and your motivation for solving it to us, by March 1st, 2022. We expect a non-hierarchic, respectful and constructive environment for the discussions, which will hopefully encourage the participants to identify and approach problems faced by early-career scientists.

EGU 2019: https://blogs.egu.eu/geolog/2019/06/05/challenging-challenges-in-earth-science-research-at-the-egu-general-assembly/

vEGU 2021: https://blogs.egu.eu/geolog/2021/07/02/crowd-solutions-to-challenges-in-earth-sciences/

What is the “Potsdam Gravity Potato”? What is a reference frame and why is it necessary to know in which reference frame GNSS velocities are provided? Geodetic data, like GNSS data or gravity data, are used in many geoscientific disciplines, such as hydrology, glaciology, geodynamics, oceanography and seismology. This course aims to give an introduction into geodetic datasets and presents what is necessary to consider when using such data. This 105-minute short course is part of the quartet of introductory 101 courses on Geodynamics 101, Geology 101 and Seismology 101.

The short course Geodesy 101 will introduce basic geodetic concepts within the areas of GNSS and gravity data analysis. In particular, we will talk about:
- GNSS data analysis
- Reference frames
- Gravity data analysis
We will also show short examples of data handling and processing using open-source software tools. Participants are not required to bring a laptop or have any previous knowledge of geodetic data analysis.

Our aim is to give you more background information on what geodetic data can tell us and what not. You won’t be a Geodesist by the end of the short course, but we hope that you are able to have gained more knowledge about the limitations as well as advantages of geodetic data. The course is run by early career scientists from the Geodesy division, and is aimed for all attendees (ECS and non-ECS) from all divisions who are using geodetic data frequently or are just interested to know what geodesists work on on a daily basis. We hope to have a lively discussion during the short course and we are also looking forward to feedback by non-geodesists on what they need to know when they use geodetic data.

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.

We want to ask and find answers to the following questions:
Which approaches and tools can be used in Earth and planetary observation?
What are the biggest challenges in bridging between scientific disciplines and how to overcome them?
What kind of participatory citizen scientist involvement (e.g. how are citizen scientists involved in research, which kind of groups are involved) 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?
How can citizen science and open science approaches and initiatives be supported on different levels (e.g. institutional, organizational, national)?

Through a wealth of geospatial data, growing computational power, and demonstrated success of application across many fields, artificial intelligence (in particular, machine learning) promises to advance our understanding of natural hazards and our ability to predict and respond to natural disasters. The ITU/WMO/UNEP Focus Group AI for Natural Disaster Management (FG-AI4NDM) is building a community of experts and stakeholders to identify best practices in the use of AI for data processing, improved modeling across spatiotemporal scales, and providing effective communication. This multidisciplinary FG-AI4NDM-session invites contributions addressing challenges related to floods, landslides, earthquakes, volcanic eruptions, tsunamis, among others, as well as multi-hazard. It also welcomes presentations on novel AI methods (including advances in automated annotation, explainability, etc.), which are hazard agnostic.

In a fast-changing environment, earth’s ecosystems are facing multiple stressors compromising the provision of essential services for mankind, and the resiliency of the natural environment itself.
Climate change, water pollution and scarcity affect biodiversity, socio-economic and climate related vulnerabilities and as a consequence, water and food security and human health.
The recent European Green Deal aims at Europe becoming the world’s first climate-neutral continent by 2050 and it does so by setting climate, energy, transport and taxation policies fit for reducing net greenhouse gas emissions by at least 55% by 2030. This program sets ambitious yet realistic targets for the next decades, auspicating the transformation of European Countries into a modern resource-efficient economy and society in line with the Sustainable Development Goals.
However, to address both the impacts as well as the causes of climate change, it is fundamental to create conditions where ecosystem services are optimized for both the local population and global objectives. Yet, the use of ecosystem services assessment in decision making might prove challenging when it comes to economic and social domains, as well as the perception and concept of natural environment may differ across disciplines. Such transdisciplinary approach plays a key role in Nature Based Solutions and opens up to the participation of multiple stakeholders in local governance, thus offering a multitude of co-benefits for the environment and for communities.
This session aims at opening a common ground between the natural, physical, social and economic sciences towards a resilient planet, by providing examples of challenges and opportunities and harmonizing best practices in this field.
We welcome transdisciplinary contributions on terrestrial, marine, and urban ecosystem services assessment that take into account the natural and the human dimension, advance in modelling complex spatio-temporal and social dynamics and transdisciplinary approaches towards nature inspired and supported solutions for social benefits and ecosystems’ resilience.

Land–atmosphere interactions often play a decisive role in shaping climate extremes. As climate change continues to exacerbate the occurrence of extreme events, a key challenge is to unravel how land states regulate the occurrence of droughts, heatwaves, intense precipitation and other extreme events. This session focuses on how natural and managed land surface conditions (e.g., soil moisture, soil temperature, vegetation state, surface albedo, snow or frozen soil) interact with other components of the climate system – via water, heat and carbon exchanges – and how these interactions affect the state and evolution of the atmospheric boundary layer. Moreover, emphasis is placed on the role of these interactions in alleviating or aggravating the occurrence and impacts of extreme events. We welcome studies using field measurements, remote sensing observations, theory and modelling to analyse this interplay under past, present and/or future climates and at scales ranging from local to global but with emphasis on larger scales.

An increasing number of single model large ensemble simulations from Global Climate Models (GCM), Earth System Models (ESM), or Regional Climate Models (RCM) have been generated over recent years, to investigate internal variability and forced changes of the climate system — and to aid the interpretation of the observational record by providing a range of historical climate trajectories that could have been. The increased availability of large ensembles also enables new and inter-disciplinary applications beyond large-scale climate dynamics.

This session invites studies using large GCM, ESM, or RCM ensembles looking at the following topics: 1) Reinterpretation of the observed record in light of internal variability; 2) forced changes in internal variability; 3) development of new approaches to attribute and study observed events or trends; 4) impacts of natural climate variability; 5) assessment of extreme and compound event occurrence; 6) combining single model large ensembles with CMIP archives for robust decision making; 7) large ensembles as testbeds for method development.

We welcome research across all components of the Earth system. Examples include topics ranging from climate dynamics, hydrology and biogeochemistry to research on the role of internal variability in impact studies, focused for example on agriculture, air pollution or energy generation and consumption. We particularly invite studies that apply novel methods or cross-disciplinary approaches to leverage the potential of large ensembles.

With recent extreme events reaching far beyond existing records, such as the Pacific Northwest heat wave and severe flooding in Western Europe, eastern US and across China, the discussion to what extent we are prepared for unprecedented extremes and whether existing methods and models are able to capture them has flared up. It is becoming increasingly essential to understand and quantify plausible rare, high-impact events for risk management and adaptation.
Methods to understand and evaluate low-likelihood extreme events have seen substantial advancements over the recent years. Event attribution studies are now providing rapid analyses of unprecedented extreme events; physical climate storylines are developed to evaluate plausible rather than likely events; causal inference is used to understand drivers of very rare events; near-miss events and potential analogues in space, historical and paleo archives are evaluated; spatial extreme value analysis and machine learning methods are applied, large ensembles representing various outcomes are generated, such as Single Model Initial-condition Large Ensembles (SMILEs); and weather prediction systems are increasingly being employed, such as the through the UNprecedented Simulated Extremes using ENsembles (UNSEEN) approach.
This session aims to bring together communities from weather prediction, climate projection, hydrology to impact and risk management, and to learn from the variety of methods to understand and quantify low-likelihood extreme events in the present and future climate. The session welcomes contributions at all temporal and spatial scales, and all types of extremes and invites novel methods – including downward counterfactuals and causal inference – as well as new results on unforeseen climate risks – including those from compound events and low-likelihood high-warming outcomes.

This interdisciplinary session brings together modellers and observationalists to present results and exchange knowledge and experience in the use of inverse methods, geostatistics and data assimilation - including machine learning - in cryospheric science.
In numerous research fields it is now possible not only to deduce static features of a physical system but also to retrieve information on transient processes between different states or even regime shifts. In the cryospheric sciences a large potential for future developments lies at the intersection of observations and models with the aim to yield prognostic capabilities in space and time. Compared to other geoscientific disciplines like meteorology or oceanography, where techniques such as data assimilation have been well established for decades, in cryospheric sciences only the foundation has been laid for the use of these techniques, one reason often being the sparsity of observations.
We invite contributions from a wide range of methodologies - from satellite observations to deep-looking geophysical methods and advancements in numerical techniques, and from topics including permafrost, sea ice and snow to glaciers and ice sheets, covering static system characterisations as well as transient processes.

The ecological stability, soil degradation, and hydrological extremes are the main driving elements and powerful tools associated with climate change on reducing or increasing the acceleration of climate change.
Climate change is a natural process, but the latest scientific research proves that it is significantly accelerated by human activity. Adequate steps can be taken by humans (for instance land use/land cover changes) in order to reduce the risks and consequences of the effects of climate change. Despite this knowledge, which is well known, progress is still slow, and the negative consequences prevail over the positive remedies.
The session should reflect, discuss, and share scientific knowledge on a local and regional scale with the aim to increase innovative knowledge thanks to multidisciplinary links at national, international, and global levels.
This session is open within a wide range of relevant scientific topics as follows:
• hydrological extremes as one of the main impacts of climate change;
• lack of precipitation or extreme precipitation - how to reduce and decrease these extremes by adequate measures;
• the connection between deteriorating ecological stability and climate change;
• new methods and procedures for reducing existing manifestations of climate change (such as soil degradation, carbon sequestration, changes in natural, agricultural, and forest ecosystems, reduction of overall ecological stability and character of the landscape);
• proposal of measures to prevent the occurrence of the above-mentioned impacts;
• the sustainability of management practices, the importance of appropriate land use management as the main tool for preventing degradation processes, floods, and droughts, improving the condition of forest ecosystems in order to increase the overall character of the landscape.

High-impact climate and weather events typically result from the interaction of multiple hazards across various spatial and temporal scales. These events, also known as Compound Events, often cause more severe socio-economic impacts than single-hazard events, rendering traditional univariate extreme event analyses and risk assessment techniques insufficient. It is therefore crucial to develop new methodologies that account for the possible interaction of multiple physical drivers when analysing high-impact events. Such an endeavour requires (i) a deeper understanding of the interplay of mechanisms causing Compound Events and (ii) an evaluation of the performance of climate/weather, statistical and impact models in representing Compound Events.

The European COST Action DAMOCLES coordinates these efforts by building a research network consisting of climate scientists, impact modellers, statisticians, and stakeholders. This session creates a platform for this network and acts as an introduction of the work related to DAMOCLES to the research community.

We invite papers studying all aspects of Compound Events, which might relate to (but are not limited to) the following topics:

Synthesis and Analysis: What are common features for different classes of Compound Events? Which climate variables need to be assessed jointly in order to address related impacts? How much is currently known about the dependence between these variables?
Stakeholders and science-user interface: Which events are most relevant for stakeholders? What are novel approaches to ensure continuous stakeholder engagement?
Impacts: What are the currently available sources of impact data? How can they be used to link observed impacts to climate and weather events?
Statistical approaches, model development and evaluation: What are possible novel statistical models that could be applied in the assessment of Compound Events?
Realistic model simulations of events: What are the physical mechanisms behind different types of Compound Events? What type of interactions result in the joint impact of the hazards that are involved in the event? How do these interactions influence risk assessment analyses?

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 (toxic) 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 (economic losses, infrastructural damages, human fatalities, pollution), 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 on damage prevention and damage reduction. In order to understand fundamental processes, 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, environmental effects, hazard management and applications like insurance issues.

This session aims to share innovative approaches to developing multi-hazard risk assessments and their components (hazard, exposure, vulnerability and capacity), and to explore their applications to disaster risk reduction.

Effective disaster risk reduction practices and the planning of resilient communities requires the evaluation of multiple hazards and their interactions. This approach is endorsed by the UN Sendai Framework for Disaster Risk Reduction. Multi-hazard risk and multi-hazard impact assessments look at interaction mechanisms among different natural hazards, and how spatial and temporal overlap of hazards influences the exposure and vulnerability of elements at risk. Moreover, the uncertainty associated with multi-hazard risk scenarios needs to be considered, particularly in the context of climate change and slow-onset hazards, such as Covid-19 and pandemics in general, characterized by dynamic changes in exposure and vulnerability that are challenging to quantify.

This session, therefore, aims to profile a diverse range of multi-hazard risk and impact approaches, including hazard interactions, multi-vulnerability studies, and multi-hazard exposure characterization. In covering the whole risk assessment chain, we propose that it will be easier to identify potential research gaps, synergies and opportunities for future collaborations.

We encourage abstracts which present innovative research, case study examples and commentary throughout the whole disaster risk cycle on (i) multi-hazard risk methodologies which address multi-vulnerability and multi-impact aspects; (ii) methodologies and tools for multi-hazard risk management and inclusive risk-informed decision making and planning; (iii) methodologies and tools for multi-hazard disaster scenario definition and management for (near) real-time applications; (iv) cross-sectoral approaches to multi-hazard risk, incorporating the physical, social, economic, and/or environmental dimensions; (v) uncertainty in multi-hazard risk and multi-hazard impact assessment; (vi) evaluation of multi-hazard risk under future climate and slow-onset hazards, including pandemics; (vii) implementation of disaster risk reduction measures within a multi-hazard perspective.

The purpose of this session is to: (1) showcase the current state-of-the-art in global and continental scale natural hazard risk science, assessment, and application; (2) foster broader exchange of knowledge, datasets, methods, models, and good practice between scientists and practitioners working on different natural hazards and across disciplines globally; and (3) collaboratively identify future research avenues.
Reducing natural hazard risk is high on the global political agenda. For example, it is at the heart of the Sendai Framework for Disaster Risk Reduction and the Paris Agreement. In response, the last decade has seen an explosion in the number of scientific datasets, methods, and models for assessing risk at the global and continental scale. More and more, these datasets, methods and models are being applied together with stakeholders in the decision decision-making process.
We invite contributions related to 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. We also encourage contributions examining the use of scientific methods in practice, and the appropriate use of continental to global risk assessment data in efforts to reduce risks. Furthermore, we encourage contributions focusing on globally applicable methods, such as novel methods for using globally available datasets and models to force more local models or inform more local risk assessment.

Hydrometeorological and geomorphological hazards account for 45% of the fatalities and 79% of global economic losses. Exacerbated by high seismic activity and rugged terrain, the Himalayan landscape is particularly susceptible to generating these events, which often transform into cascading hazards—an initial event causes a downstream hazard chain, e.g. glacial lake outburst floods to debris flows. These hazards interfere with increasing population pressure and expansion of settlements along rivers and new infrastructure developments such as roads and hydropower projects. Rising temperatures and changes in weather patterns in the wake of global warming likely elevate risks from hazards such as landslides, glacial lake outburst floods, riverine and flash floods. The complexity of these hazards and their underlying processes demand scientific efforts and approaches from multiple disciplines.

Multidisciplinary approaches and methodologies are important to holistically estimate and predict hazard events and interactions of multiple hazards, and to understand how vulnerable societies cope and respond to these hazards in the Himalayan region.
This session aims to bring together expertise on approaches, methods, and data to advance the understanding of the impacts and changes in the extremely high mountain landscapes, with a particular focus on the trends of hydro-geomorphological disasters on the Himalayas and their societal impacts.

We welcome contributions from research topics (but not restricted to):
-hydro-geophysical modeling (landslides, glacial lake outburst floods, riverine and flash floods)
-extreme event modeling
-remote-sensing-based observations
-risk/vulnerability assessment
-theories and models of reducing vulnerabilities and adaptation to natural hazards
-innovative data approaches to integrate natural and social science perspective
-recovery to natural hazards, in particular, usage of longitudinal data methods

The session is closely linked to the NHESS special issue “Estimating and Predicting Natural Hazards and Vulnerabilities in the Himalayan Region”. We encourage all session contributors to support this issue.

Increasing effects of climate change, urbanization, and increased interconnectedness between ecological, physical, human, and technological systems pose major challenges to disaster risk management in a globalised world. Economic losses from natural hazards and climate change are still increasing, and the recent series of catastrophic events across the world together with the COVID-19 crisis has manifested the urgent need to shift from single-hazard-based approaches to new and innovative ways of assessing and managing risk based on a multi-hazard and systemic risk lens. This calls for novel scientific approaches and new types of data collections to integrate the study of multiple natural processes and human influences triggering hazards, including studies of ecological, physical, socioeconomic, political, and technical factors that shape exposure and vulnerability of humans, sectors and systems across borders and scales.

Tackling the above challenges, this session aims to gather the latest research, empirical studies, and observation data that are useful for understanding and assessing the interplay between multiple natural hazards and social vulnerability to: (i) identify persistent gaps, (ii) propose potential ways forward, and (iii) inform resilience building strategies in the context of global change.

Climate-induced geohazards are known to increase with climate change causing more intense rainfall and more frequent extreme weather events. Use of vegetation on potentially unstable slopes and along stream banks is an example of Nature-Based Solutions (NBS) that can mitigate climate induced geohazards due their role at the soil-atmosphere interface. Vegetating slopes or stream banks are also key for ecological restoration and rewilding, providing several additional co-benefits. However, researchers in different fields of science or practitioners do not easily communicate, even though they are addressing aspects of the same problem.
Interdisciplinary research and bilateral communication are needed to document the effects of vegetation in hazard-prone areas in a measurable and applicable manner. These NBS must have an ecological approach, where in the long-term perspective, a multiple approach for biodiversity and ecosystem services will give mutual synergies.

This session aims to stimulate interdisciplinary communication, knowledge exchange and dissemination on plant-soil-atmosphere interaction, with focus on vegetation mitigating climate-induced geohazards, particularly shallow landslides and erosion.
Contributions documenting how vegetation and roots can be beneficial also in land use planning, restoration ecology, climate change adaptation are welcome within the fields of geotechnical engineering, plant ecology, biodiversity, alpine timberline, hydrogeology and agronomy.
Interaction between research and industry, with involvement of NBS entrepreneurs, are particularly welcome.

Topics of interested are listed, including, but not limited to:
• Experimental, either laboratory or field, or numerical investigation of plant-soil-atmosphere interaction and its relation to slope or bank stability
• How to implement morpho-mechanical parameters of plants in engineering design?
• Measuring and quantifying the effects of vegetation as NBS to mitigate climate-induced geohazards
• Tools, approaches, and frameworks demonstrating how vegetation can be used to mitigate climate-induced geohazards, while providing additional co-benefits
• Investigation on upscaling potential from laboratory to slope and catchment scale
• Case studies of restoration or stabilisation works, especially on design principles and performance assessment
• Ensuring interdisciplinary interaction and mutual synergies for studies containing vegetation as NBS among different disciplines