Inter- and Transdisciplinary Sessions
Disciplinary sessions

HS – Hydrological Sciences

Programme Group Chair: Alberto Viglione

Henry Darcy Medal Lecture by Alberto Guadagnini
Convener: Alberto Viglione
John Dalton Medal Lecture by Paul D. Bates
Convener: Alberto Viglione
HS Division Outstanding ECS Award Lecture by Andrea Cominola
Convener: Alberto Viglione

HS1 – General Hydrology

Sub-Programme Group Scientific Officer: Alberto Viglione

HS1.1 – Hydrology in Climate Change

Sub-Programme Group Scientific Officer: Alberto Viglione


* This is a solicited presentation and panel discussion session. Submitted contributions will be considered for a poster session

Hydrological process research and modelling play a key role in the management and sustainability of future water resources. This scientific session aims to explore the intricate interplay between scales of relevance in the context of future water resources management. By bringing together experts from surface hydrology, hydrogeology, eco-hydrology, and socio-hydrology, this session seeks to foster a dialogue on the pertinent scales that shape the availability, distribution, and utilization of future water resources.
The oral part of the session is composed of solicited presentations followed by a panel discussion. We solicit however poster contributions for a vibrating poster session.

Solicited authors:
Ilja van Meerveld,Gemma Coxon,Inge de Graaf,Jesús Carrera
Convener: Bettina Schaefli | Co-conveners: Axel Bronstert, Andreas HartmannECSECS, Alberto Viglione

Hydrology has significantly changed over the last few decades and is expected to continue evolving in the future due to climatic changes. With the increasing availability of observed streamflow data, remote sensing of evapotranspiration, water storage estimates, and the rapid advancement in global Earth system and land surface models, researchers now have a powerful toolset to understand hydrological changes on both regional and global scales.
However, numerous conflicting results exist between observational-based studies and global modeling results. These disparities highlight significant knowledge gaps in our understanding of hydrological processes in a changing climate. This session provides a valuable opportunity to address hydrological change topics in coordination with efforts from different regions worldwide to synthesize global-scale results.
We invite submissions covering a wide range of topics, including, but not limited to, the following topics:
1. Advanced techniques (ground observations and remote sensing) for more accurate estimation of hydrological components (precipitation, evapotranspiration, streamflow, and water storage changes) at catchment, regional, and global scales.
2. Responses and feedbacks of hydrological components to climate change and anthropogenic activities.
3. Projections of regional and global hydrological changes in the near and distant future.
4. Benchmarking hydrological modeling results using state-of-the-art observations.
5. Hydrological processes in hotspot regions such as the Tibetan Plateau, the Arctic, the Amazon and the regions with heavy irrigations.

Convener: Yongqiang Zhang | Co-conveners: Günter Blöschl, Jan Seibert
HS1.1.3 EDI

Global climate change causes an increasing frequency and intensity of floods and droughts. Both are strongly linked and have the potential to reinforce each other. Floods and droughts cover the entire hydrological spectrum and share many similarities and links between the two types of extremes. Nevertheless, management strategies and technical compensation and mitigation measures are often thought only from one side of the extreme, like flood retention basins releasing the stored flood water within days instead of keeping it in the region. On the other hand, managed aquifer recharge, especially when applied in drinking water catchments, is often turned off during flooding events, due to suspected contamination risks to the aquifer. Additionally, natural wetlands and/or the restoration of degraded wetlands can influence catchment water availability and flood and drought severity. Successful management of regional water resources seems to require approaches, tools, and management strategies that combine techniques from flood protection and drought prevention, i.e., combining water retention, treatment, and infiltration in subsurface storage systems (ideally aquifers) for long-term high-quality uses.

For this session we welcome contributions focusing on the whole strategic and operative management processes of these extreme events including:
• Field studies and modelling experiments for the hydrological hazards, sensitivity, and their consequences
• Interdisciplinary approaches for managing scarce water resources and flooding events and to support decision-making (e.g., public water supply, agriculture, industry, or environmental water use)
• Examples from coupling flood dams with managed aquifer recharge (Flood-MAR) including its legal framework
• Development of fast and robust infiltration and treatment schemes for flood waves
• Development of fast in-situ analytical tools to measure the water quality of the infiltrated water
• Mitigation measures, ranging from technical solutions like storm water storage to an adaptive design of urban and rural areas or operative-working forecasting systems
• Studies that evaluate the role of wetlands in the context of water availability and extreme hydrological events

Convener: Lea AugustinECSECS | Co-conveners: Scott Ketcheson, Rudy Rossetto
HS1.1.4 EDI

The long-term effects of climate change, extreme events, and seasonal weather variations have a profound impact on the water quality of rivers, lakes, and reservoirs. Consequently, there is an urgent need for tools that can anticipate these impacts and address the resulting environmental changes, facilitating effective water management that safeguards the critical ecosystem goods and services provided by freshwater sources. Unfortunately, scientific studies often overlook the influence of climate change on water quality. To address this gap, this session aims to explore research results related to the impact of climate change on water quality. We enthusiastically welcome climate attribution results, studies utilizing data-driven and remote sensing techniques, as well as model projections investigating climate change on local to global scales. Additionally, we are interested in water quality studies conducted within the context of the Inter-Sectoral Impact Model Intercomparison Program (ISIMIP), encompassing both regional and global water sectors.

Convener: Albert NkwasaECSECS | Co-conveners: Michelle van Vliet, Rohini Kumar

Climate change presents one of the most pressing global challenges, with far-reaching implications for both natural and human systems. Among the myriad consequences of climate change, the rise in climate extreme events has been well-documented through observational and modelling studies. These extremes, ranging from heavy precipitation and floods to heatwaves, wildfires, and droughts, exert profound and often devastating impacts on agriculture and the society. In this context, understanding the intricate connectivity between agricultural and hydrological systems under the influence of climate change has emerged as a critical research imperative, and necessitates a multidisciplinary approach.

Recent advancements in remote sensing, machine learning, and the development of process-based models offer immense potential for in-depth investigations into agriculture and hydrological systems in a changing climate. This session aims to solicit and showcase research contributions that employ diverse methodologies, particularly Earth Observations, machine learning approaches, and numerical/statistical models, to monitor, simulate, and predict the connectivity between agricultural and hydrological systems, spanning various spatiotemporal scales.

We invite researchers to engage in this session and contribute to the collective understanding of how climate change impacts the intricate relationship between agricultural and hydrological systems. Topics of interest include, but are not limited to:

1. Observational insights: Present observational evidence and case studies that shed light on observed climate extremes, their effects on agricultural systems, and hydrological responses.
2. Machine learning applications: Innovative applications of machine learning algorithms to analyze and predict the impacts of climate extremes on agriculture and hydrology.
3. Numerical and Statistical Modeling: Utilize numerical and statistical models to simulate and project future scenarios of climate-induced changes in agricultural and hydrological systems.
4. Scaling Effects: Investigate the interconnectedness of agricultural and hydrological systems across various spatial and temporal scales, elucidating regional and global implications.
5. Adaptation and resilience: Discuss strategies for adapting agriculture and hydrology to climate extremes, emphasizing the importance of building resilience in these systems.

Convener: Guoyong Leng | Co-conveners: Jian Peng, Shengzhi HuangECSECS, Xuejun ZhangECSECS

Hydrological extremes including both drought and flood already pose a significant risk globally, one that is predicted to increase as climate change leads to an increase in severe climate events. With the significant environmental, social and economic cost associated with such extremes, there is an increasing need for sustainable catchment management strategies that attenuate flow regimes, minimising the risk of flooding and ensuring a sustainable water supply and ecosystem resilience during drought periods. Consequentially in recent years there has been a notable uptake in interest in the value of ‘nature-based solutions’ at the catchment scale that work with or are inspired by nature to restore the natural functioning of our anthropogenically modified landscapes, providing both greater hydrological resilience to extreme events but critically also a host of additional benefits, particularly for biodiversity, climate and society.

As the popularity of nature-based solutions increases, trans-disciplinary research is required to: (1) determine what constitutes a nature-based solution; (2) maximise the effectiveness of such solutions and how they can be implemented alongside existing water management strategies; and (3) consider the social factors that are inherent in the successful implementation of nature-based solutions, overcoming the conflicts or barriers that may otherwise be associated with their implementation.

This session aims to attract abstracts that define the state of the art for current research addressing hydrological nature-based solutions and identify gaps in understanding that will need to be addressed to ensure their success. We especially welcome submissions that whilst focusing on hydrological nature-based solutions take into account the co-benefits that may be delivered.

Convener: Diego PaniciECSECS | Co-conveners: Alan PuttockECSECS, Roger AusterECSECS, R.E. Brazier

The effects of climate change highlight the importance of developing a resilient design approach for buildings, both in dense urban areas and rural communities. Nature-based solutions (NBSs) can help in this as an adaptation measure, providing multiple benefits at building scale. Increasing the applications of green walls and green-blue roofs can reduce heat stress, improve rainwater and wastewater management and drive the communities towards the concept of circular economy and self-subsistence.

This session aims to share and discuss the most recent advances in NBSs that increase building resilience and sustainability in the urban environment. Therefore, we aim for a session including researchers from different fields such as engineering and architecture, natural sciences such as microclimatology and meteorology, and social/psychological science. We encourage also those involved in policymaking to submit a contribution, to have an integrated approach to buildings development.

Our focus will primarily be on solutions that not only improve routine building management but also make meaningful contributions to the mitigation s of extreme events, like extreme urban heat stress (UHI/heat events) or extreme precipitation events and local flooding. Submissions may include (but not restricted to) contributions on:

- Laboratory, field measurements and numerical modelling studies (like microclimatic or hydrodynamic simulations) on green walls and green-blue roofs and other NBSs for rainwater management, wastewater treatment, thermal control, edible vegetation production, energy production
- Qualitative research like user- or agent-based approaches that investigate the potentials and effects of NBSs for climate change adaptation and improving thermal comfort, and further challenges of the water-energy nexus on this small/building scale.
- Urban areas mapping (e.g. GIS applications) or modelling for buildings urban management (BIM applications)
- Investment and cost return of NBS application to buildings
- Life-Cycle-Assessment (LCA) analysis
- Quantitative analysis on possible sanitary risks innovative wastewater treatment and reuse solutions at local scale
- Buildings retrofitting projects or real-scale applications
- NBS social acceptance

In essence, our session aims to explore the multifaceted aspects of NBSs in the context of building resilience, with particular emphasis on their impact, feasibility, and sustainability.

Co-organized by ERE1
Convener: Elisa CostamagnaECSECS | Co-conveners: Francesco BuscaECSECS, Nils EingrüberECSECS, Bernhard PucherECSECS

Lakes are a major component of the hydrosphere which are able to accumulate and transfer energy and matter to and from other spheres of the environment. Lakes, especially the largest ones, have higher thermal inertia and longer residence times than those of the other inland water bodies such as rivers and lagoons, thus they act as buffers in the inland waters transport network. As such, they play an important role in the global water cycle and in regulating biodiversity, availability and quality of water resources, and provision of ecosystem services. Water temperature is one of the most commonly used indicators to assess the impact of climate change on the physical and ecological functioning of lakes. Due to the ongoing climate change and anthropogenic pressures, lake thermal dynamics have been considerably impacted, which may have adverse effects on aquatic ecosystems.
The main objective of the current special issue is to present the results of studies that investigate the responses of lake thermal dynamics to climate change using multiple techniques (e.g., field measurements, remote sensing, and modelling). We welcome any related researches in the proposed topic, e.g., studies analyze lakes around the globe, discuss regional differences, and also present novel insights for lakes in given regions in an era of climate change. The topics may cover water temperature, vertical stratification and mixing, ice phenomenon, and their responses to climate change, especially during extreme climatic events (e.g., heatwaves). Novel methods to quantify the impact of climate change on lake thermal dynamics are especially welcomed. Our goal is to promote the development of interdisciplinary approaches for lake thermal researches in a changing climate.

Convener: Senlin ZhuECSECS | Co-conveners: Yi Luo, Mariusz Ptak, Mariusz Sojka

This session focuses on the many environmental and ecological challenges linked to shrinking lakes around the world. In the face of intense droughts, increased evaporation with warming temperatures, and greater demand on water resources, lakes worldwide are drying, exposing surrounding regions to diverse consequences that include threats to human health from increased dust emissions and deteriorating water quality. We view this as an opportunity to meet and share common and unique challenges from the many locations in the world impacted by this problem—to work toward solutions and draw further global attention to the issues. Presentations will include, but are not limited to, those describing case studies from specific lake systems experiencing dramatic and rapid declines in size, water quality, and the attendant deleterious environmental impacts. Additional themes include those addressing the common threads that run through these settings, such as increasing salinity and nutrient levels, controls on the amounts and compositions of increasing dust loads, harmful microbiological/biogeochemical effects, dwindling resource availability (e.g., for agriculture), sociopolitical pressures, ecological degradation within the lakes and beyond, and current and future threats to large human populations, among others.

Co-organized by BG4
Convener: Timothy W. Lyons | Co-conveners: Charles Diamond, Caroline Hung, Virginia Gewin

River deltas historically housed many of the Earth’s important ecosystems. The Anthropocene saw these grand terminals of the fluvial systems taking on a new role as now; they also support human lives while facing many intensifying pressures from natural systems, including floods, droughts, or salinity intrusion, that can heavily affect deltas’ Indigenous freshwater ecosystems while rendering the land inarable or even inhabitable. These negative impacts are exacerbated by human development and climate change induced sea level rise, increasing salinity and ground subsidence. Surface and groundwater resources for both domestic and agricultural purposes over overused, saline intrusion is increasing and land use for agriculture competes with nature and urbanization. How can we effectively meditate these impacts via Mitigation and adaptation? Or can we expect innovative strategies, such as using a water and food systems approach and Nature-based Solutions (NbS), to harvest the benefits of both effectively?
This session provides the opportunity for delta researchers to get updated on recent advancements of research related to adaptation and mitigation strategies in global mega deltas while providing ecosystem services (a.o. food supply) as they are taking on the rising climate hazards in the Anthropocene. We will discuss theoretical assessment studies, actual on-site interventions, innovative solutions and viewpoints of factors that may fuel/hamper the advancement of the delta research discourse. Contributions to addressing the following topics are welcome:
• Case studies reporting on-site observations.
• Theoretical assessments, including modelling of innovative mitigation and/or adaptation.
• Critical reviews of significant studies with clear focuses
• Reports of advancements in science-policy dialogues
• Innovative solution for adaptation and / or mitigation strategies

Convener: Loc Ho | Co-conveners: C. Terwisscha van Scheltinga, Md Feroz Islam, Indrajit Pal, Edward Park

In an era of climate uncertainty and evolving human influence on natural environments, understanding the dynamics of long-term climatic and hydrologic change has become critical. This session has a focus on real-world case studies and applications, though which we seek to explore the multifaceted implications of climate change on water availability, aquatic environments, and the dynamics of socio-ecological riverine systems.

We invite tangible examples of climate change impact assessments on hydrological and related systems, including resource management, policy and adaptation. We hope to showcase research across diverse geographical regions and varied contexts to facilitate sharing of methods, insights and lessons learned.

Submissions are encouraged across the full spectrum of available techniques, including so-called “bottom-up” approaches to decision making under deep uncertainty. Studies applying novel modelling paradigms, innovative risk assessment frameworks, or characterising multiple (compound) sources of risk are particularly encouraged. By showcasing diversity, we aim to foster a practical understanding of the implications of long-term change, leading to better decision-making for an uncertain future.

Convener: Gabrielle BurnsECSECS | Co-convener: Keirnan FowlerECSECS

HS1.2 – Innovative sensors and monitoring in hydrology

Sub-Programme Group Scientific Officer: Alberto Viglione

HS1.2.1 EDI

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.

Co-organized by AS5/GI6
Convener: Rolf Hut | Co-conveners: Theresa Blume, Marvin ReichECSECS, Andrew Wickert

Effective management of river systems for water supply, ecological and environmental protection and flood control often relies upon empirically derived discharge datasets. In recent years, many new or substantially improved methods have become available that can increase the effectiveness and efficiency of these measurements.

In this session, participants will have the opportunity to learn about and use in a river environment state-of-the-art flow measurement techniques such as ADCP (Acoustic Doppler Current Profiler), Image-Processing based methods (e.g. LSPIV, STIV, PTV), radar and chemical/dilution methods. The issues related to the different measurement techniques will be discussed, as well as the accuracy and uncertainty of the results obtained.

Participants are invited to test the equipment provided or bring their own equipment and demonstrate it. New and innovative measurement technologies are of course more than welcome. A competitive element will be included, with participants invited to submit their estimated flow and uncertainty, with the winner being the estimate that most closely matches a reference streamflow value.

The fieldwork site will be within a few kilometers of the EGU conference venue, and transport will be provided.

Convener: Salvador Peña-Haro | Co-conveners: Gabriel Sentlinger, Christoph Sommer

Hydrological monitoring is crucial in understanding the intricate nature of Earth's water cycles. It has a significant impact on the formation and transformation of drainage systems and landforms over time. Recently, remote-sensing sensors such as geophones, seismometers, distributed acoustic sensing (DAS), and underwater acoustic hydrophones have provided a new view compared to traditional monitoring techniques such as acoustic Doppler stream-flow devices, piezometers, rain gauges, and water-level gauges. Vibration/acoustic sensing presents an exciting and unparalleled opportunity to uncover previously obscured signatures of hydrological processes, encompassing turbulent flow, bedload transport, groundwater fluctuations, snowmelt, rainfall, debris flow, calving iceberg, and landslide dam breaches, all while offering the advantage of remote monitoring, eliminating the need for intimate proximity to these processes and reducing the associated risks to human life and equipment damage.

This session focuses on applying vibration/acoustic monitoring to hydrological processes, covering observations, investigations, physical modeling, and practical implementations. We would like to invite contributions that explore the utilization of vibration/acoustic sensing in hydrological-related processes. These novel and comprehensive observations have the potential to enhance our understanding of the Earth's water cycle.

Co-organized by GI1/GM11/SM5
Convener: Jui-Ming ChangECSECS | Co-conveners: Luc IllienECSECS, Ron NativECSECS, Wei-An Chao
HS1.2.4 EDI

Fast and reliable access to large datasets is the fundament of hydrological research. According to the FAIR principles, sustainable research data should be findable, accessible, interoperable, and reusable in a way that the reproducibility of research experiments is guaranteed. There are several global and regional hydrological databases that are providing harmonized data from different data sources. Thereby they serve as archives, as well as an intermediate between data providers and users. The great value of the databases is shown in the diversity of studies, assessments and data products originating from the provided data, supporting the integrative understanding of the hydrologic cycle. At national and international levels, these databases are also used for the assessment of water resources for policy guidance.

This session aims to show ideas, concepts, efforts and challenges in developing data products as well as demonstrating the benefit of setting up, maintaining networks, and sharing data in order to support the data acquisition ambitions of data centres. This session contributes to IHP IX (2022 - 2029) goal, which puts science, research and management into action for a water secure world.

We invite contributions on the following topics:

1. Data services: processing, quality assurance and data discovery
- Methods and challenges of collection and provision of reliable data and metadata to the science community
- Improvement in database services e.g. versioning, dissemination or integration of new features that are relevant to science and research applications
- Development of ontologies and reference datasets showing how metadata can be used to streamline data findability

2. Tools and data-derived products for integrative observation of the hydrologic cycle
- Integrated data products derived from the analysis of existing databases
- Tools and platforms for data exchange and exploration
- Collaborative and interoperable data platforms to create a contextual and unified analysis for better decision making

3. From data to action: role of data services in operational hydrology
- Data-driven studies and projects that aim to support decision making and policy formulation
- Studies showing the contribution of large data services to assessing water resources at national, regional and global scales
- Case studies demonstrating the benefits of operational observation networks to improve local, regional and global hydrological products and services

Co-organized by ESSI2/GI2, co-sponsored by WMO
Convener: Claudia FärberECSECS | Co-conveners: Tunde OlarinoyeECSECS, Moritz Heinle, Claudia Ruz VargasECSECS, Stephan Dietrich

Understanding the complex interactions between soil-plant-atmosphere compartments and human activities is critical for ensuring the sustainable management and preservation of ecosystem functions and services. Global climate change and human activities threaten the functions and services of our terrestrial ecosystems. The complexity and holistic nature of the consequences have been difficult to assess so far, as simplified experimental approaches and long-term observations have methodological constraints and often focus on a very limited set of response variables.
Larger and more realistic experimental systems such as in situ lysimeters or ecotrons can supply a wide range of high quality continuous and high-resolution data sets on ecosystem services and functions in the Earths critical zone. Individual facilities and larger networks such as TERENO-SOILCan (lysimeter) or ANAEE’s ecotron experimental infrastructures provide a unique platform for a variety of interdisciplinary research to better understand the dynamic of ecosystems.
The session will focus on ecosystem research based on lysimeters and ecotron experiments, including model application. Additionally, we want to address upscaling approaches from lysimeter to landscape scale or between several types of ecosystem experimental infrastructures (e.g., lab, field, or control environments), uncertainty assessments, representativeness of lysimeter-scale observations, and comparability of water, and greenhouse gases flux to in situ measurements. We welcome contributions that (1) assess and compare terrestrial ecosystems functioning and services, (2) focus on water and solute transport processes, as well as greenhouse gases within the soil-plant-atmosphere continuum, including processes such as non-rainfall water inputs (i.e., dew, fog, soil water vapor adsorption), (4) develop new techniques for analyzing lysimeter and ecotron observations, (5) including ecosystem or hydrological modelling approaches that use in-situ observations from lysimeters or ecotrons.

Co-organized by BG2
Convener: Jannis GrohECSECS | Co-conveners: Francois Rineau, Reinhard Nolz, Thomas Puetz, Alexandru Milcu

HS1.3 – Cross-cutting hydrological sessions

Sub-Programme Group Scientific Officer: Alberto Viglione

HS1.3.1 EDI

Ensuring safe water supply for human and environment, and protecting them from water hazards have become more challenging due to intensified impacts of climate change, globalization, and population growth. Hydrological knowledge is needed more than ever to address water security issues. However, scientific knowledge on resilience and water security is fragmented in discipline, people, and place. There is a substantial lack of synthesis and easily digestible scientific messages among hydrologists, across disciplines and from scientists to practitioners, decision-makers and the general public. Hence, there is a need for the hydrological research community to better link local hydrological research with global patterns of the water cycle, and further, to provide science-based water-centric decision support.

Therefore, the International Association of Hydrological Sciences (IAHS) is dedicating the next scientific decade to science for solutions. The short name is HELPING, and stands for Hydrology Engaging Local People IN one Global world. It aims to identify local water problems in holistic/system analyses (i.e., linking local and global scales, disciplines and needs, and connecting the dots), search for solutions, be bold and push boundaries to make an impact and connect people across and within regions (e.g., Global North, Global South, North-North, South-South) and provide synthesis to answer the needs of society for sustainable development, safety and security. The topic and vision of the new decade was an outcome of several on-line interactions and workshops during 2023 using a strategic planning approach, as summarised and documented at https://iahs.info/. To date, some 30 working groups have been suggested by the global hydrological community.

This session invites contributions related to the three major themes of HELPING, which all aim at understanding hydrological diversity and integrating knowledge across scales and regions to overcome the water crisis by:
(1) recognising global and local interactions;
(2) finding holistic solutions for water security;
(3) applying cross-cutting methods for facilitation, e.g. science communication, integrating new technology and fostering local co-creation processes.
In particular, we encourage submissions from early career scientists, suggested working groups, and studies that include transdisciplinary and applied experience for solving environmental and societal challenges related to water.

Co-sponsored by IAHS
Convener: Christina Anna OrieschnigECSECS | Co-conveners: Berit Arheimer, Moctar DembéléECSECS, Salvatore Grimaldi, Fuqiang Tian
HS1.3.2 EDI

Hydrological models often treat landscapes as static backgrounds on which hydrological processes play out. This is perhaps natural in the sense that hydrologic response is often described with respect to short-term forcing like rainfall, snowmelt, and diurnal changes in evaporation. However, landscape morphology, as well as soil and ecosystems, are constantly changing, albeit sometimes not on human timescales. These processes may be related to, among other things, vegetation (seasonal to centennial timescales), human activities (seasonal to millennial), weathering and soil formation (centennial to millennial), or landscape evolution (millennial to millions of years). Because all of these processes together shape the critical zone and affect how it functions, bridging gaps between short term processes and longer-term environmental change is essential for understanding landscapes and maintaining their ability to sustain life. This also includes a better understanding of tipping points and memory effects within these systems.

We invite contributions that use field measurements, modeling, or theory to explore how (comparatively) rapid hydrological and human-directed processes are the result of or produce longer term landscape change as well as possible feedback cycles between these processes. We hope to use this space to discuss how we can better achieve coupling and understanding across timescales and a broad range of fields, through new computational methods, modeling theories, and innovative field study design.

- How landscape-scale changes due to climate change or human activity affect water flow paths and soil erosion and vice versa
- The role of hydrologic variability in selecting for certain vegetation communities
- Links between groundwater flow and the development of soil and weathering profiles and vice versa
- The cumulative effects of hydrological events on critical zone structure and landscape evolution

Co-organized by GM5/SSS10
Convener: David LitwinECSECS | Co-conveners: Caroline FenskeECSECS, Hongkai Gao, Clement Roques
HS1.3.3 EDI

Many papers have advised on careful consideration of the approaches and methods we choose for our hydrological modelling studies as they potentially affect our modelling results and conclusions. However, there is no common and consistently updated guidance 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, despite their very justified existence, none of the proposed methods have become quite as common and indispensable as the split sample test (KlemeŠ, 1986) and its generalisation to cross-validation.

This session intends to provide a platform for a visible and ongoing discussion on what ought to be the current standard(s) for an appropriate modelling protocol that considers uncertainty in all its facets and promotes transparency in the quest for robust and reliable results. We aim to bring together, highlight and foster work that develops, applies, or evaluates procedures for a trustworthy modelling workflow or that investigates good modelling practices for particular aspects of the workflow. 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 and/or reproducible workflows
(6) Examples of adopting the FAIR (Findable, Accessible, Interoperable and Reusable) principles in the modelling chain
(7) Investigating subjectivity and documenting choices along the modelling chain and
(8) Uncertainty propagation along the modelling chain
(9) Communicating model results and their uncertainty to end users of model results
(10) Evaluating implications of model limitations and identifying priorities for future model development and data acquisition planning

Convener: Diana SpielerECSECS | Co-conveners: Janneke RemmersECSECS, Keirnan FowlerECSECS, Wouter KnobenECSECS, Lieke MelsenECSECS
HS1.3.4 EDI

This session focuses on advances in theoretical, methodological and applied studies at the synergistic interface among physical, analytical, information-theoretic and systems intelligence approaches to system dynamics, hazards and predictability across Hydrology and broader Earth System Sciences.

Special focus is given to unveil complex system dynamics, regimes, transitions, extremes, hazards and their interactions, along with their physical understanding, predictability and uncertainty, across multiple spatiotemporal scales.

The session encourages discussion on interdisciplinary physical and data-based approaches to system dynamics across 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 and systems intelligence.

The session further encompasses practical aspects of working with systems intelligence and information theoretic approaches for model evaluation and uncertainty analysis, causal inference and process networks, along with hydrological and geophysical automated learning, model design, prediction and decision support.

Contributions are gathered from an interdisciplinary community working with diverse approaches ranging from dynamical modelling to data mining, machine learning, artificial intelligence and beyond along with their interconnections with physical process understanding in mind.

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.

Co-organized by ESSI1/NP5
Convener: Rui A. P. Perdigão | Co-conveners: Julia Hall, Mohammad Azizur Rahman, Maria KireevaECSECS, Cristina PrietoECSECS
HS1.3.5 EDI

This session is dedicated to the comprehensive investigation of small-scale transport processes governing the movement of plastics (ranging from nano- to macroplastics) within the aquatic environment. While we aim to place special emphasis on laboratory experiments and modeling approaches, we also welcome presentations employing additional methodologies such as field work, and contributions focused on theoretical concepts.

The presentations will revolve around understanding and characterizing plastic movement, considering influential factors like particle size, shape, density, and environmental conditions such as temperature, salinity, flow velocities, water turbulence and suspended sediment concentrations. Additionally, relevant biological and chemical processes will be taken into account. Key processes to be addressed include sedimentation, resuspension, biofouling, aggregation and fragmentation, along with other interactions between plastics and the environment that may influence the transport and ultimate fate of plastic pollutants.

Beyond the presentation of research findings, this session will also focus on advancements in laboratory and modelling techniques, highlighting improvements in accuracy, complexity, and spatial-temporal resolution. Cutting-edge modelling approaches tailored to simulate the intricate transport dynamics of plastics in aquatic environments will be showcased.

Through engaging discussions, the session aims to enhance our comprehension and predictive capabilities, while also identifying unresolved questions and paving the way for future research endeavors in this vital area of study.

Convener: Uwe Schneidewind | Co-conveners: Antonia Praetorius, Daniel ValeroECSECS, Mário J Franca, Kryss WaldschlägerECSECS
HS1.3.6 EDI

Globally, agriculture uses up to 80% of freshwater, depleting both surface water and groundwater resources. Protected agriculture (plastic tunnels, glasshouses, etc.) reduce irrigation water usage up to 90% with similar yield compared to open field agriculture. With an increasing human population and climate change driving more severe and frequent hazardous meteorological phenomena, protected agriculture can offer technological solutions towards food security and sustainable water resources management.

However, important research gaps exist to comprehensively understand the effects of protected agriculture on water quantity and quality at the plot and catchment scale. Greenhouses alter the water budget terms (e.g., runoff, evapotranspiration, soil moisture storage, infiltration). Agricultural contaminants (e.g., plant protection products and fertilizers) use and fate are driven by the management of the environment inside the greenhouse rather than external meteorological conditions. The current process-understanding is often implemented in decision support systems used to recommend fertigation volumes at the greenhouse scale. But the upscale of such knowledge at the catchment scale is neglected or substantially simplified.

Another issue concerns the lack of large-scale land use and land cover maps indicating the presence of greenhouses, which hinders the capability to analyse sustainability questions as well as to simulate their impacts in realistic scenarios. For the purpose of greenhouse mapping, satellite remote sensing data and suitable machine learning algorithms have been used, although some challenges for large-scale mapping remain. In contrast to the advances in leveraging earth observation and machine learning techniques on the large-scale mapping and monitoring of conventional land uses, there remains significant potential for such applications within greenhouse contexts.

This session invites contributions that improve our quantitative understanding of the hydrological and contaminant transport impacts of protected agriculture, soil-bound and soil-less, through:
1) experimental studies and environmental monitoring;
2) numerical modelling of water use and water-saving strategies as well as fate and risk mitigation of agricultural contaminants (including sustainable alternatives such as organic production)
3) advances and applications of greenhouse mapping and monitoring methods exploiting remote sensing data and deep learning algorithms.

Convener: Daniele la CeciliaECSECS | Co-conveners: Maarten Braakhekke, Xiaoye TongECSECS, Caroline van der Salm
HS1.3.7 EDI

Quantifying and understanding the impacts of changing water availability across space and time is critically important for ensuring that there is enough water of suitable quality to meet human and ecosystem demands now and in the future. This session invites papers that explore spatial and temporal variability in water supply and demand, identify the factors driving this variability, and assess the vulnerability and resilience of human populations and ecosystems to water shortages and degradation of water quality across scales ranging from local to regional to continental. Studies applying integrated modeling approaches to quantify and couple supply and demand in support of water management are especially encouraged. Also of interest are integrated assessment methods including vulnerability assessment, scenario analysis, indicators, and the water footprint to name a few. In addition, we welcome submissions that present novel approaches for projecting future water supply and demand in the context of changing climate, land use, population growth, and other potential drivers of change.

Solicited authors:
Joseph Alcamo
Convener: Matthew Miller | Co-conveners: Olivia MillerECSECS, Caroline van Bers

The dynamic interplay between natural forces and human activities profoundly impacts the quantity and quality of water resources in our landscapes. As we seek to ensure the sustainability of these vital resources, it becomes crucial to manage and understand the multifaceted changes occurring within our watersheds. This session delves into the intricate web of relationships between landscape transformations and their effects on the Critical Zone (CZ), specifically focusing on water quantity and quality. We welcome and appreciate contributions related to the following key aspects:
1. Watershed Analysis: Investigate water flows and nutrient concentrations in watersheds to assess CZ changes affecting biogeochemical cycles.
2. Stakeholder Impact: Examine how stakeholders' preferences and perceptions influence landscape transitions and water resource associations.
3. Social-Environmental Nexus: Explore landscape transition's intervention in hydrological processes and its social implications.
4. Climate and Human Influence: Understand how climate and human activities affect watershed management, nutrient cycling, and land use.
5. Innovative Education: Develop pedagogies for modeling environmental, engineering, and societal dynamics.
6. Sustainable Solutions: Discuss pathways to prevent, alleviate, and mitigate water resource challenges for sustainable development.

Convener: Jr-Chuan Huang | Co-conveners: Tim White, Yuichi Onda, Fi-John Chang

HS2 – Catchment hydrology

Sub-Programme Group Scientific Officers: Björn Guse, Miriam Glendell

HS2.1 – Catchment hydrology in diverse climates and environments

Sub-Programme Group Scientific Officers: Björn Guse, Miriam Glendell

HS2.1.1 EDI

A large proportion of the global stream network ceases to flow periodically. These systems range from near-perennial streams with infrequent, short periods of zero flow to streams that experience flow only episodically after large rainfall events. The onset of streamflow in intermittent streams can affect the quantity and quality of water in downstream perennial rivers. Intermittent streams also support a unique and high biodiversity because they are coupled aquatic-terrestrial systems. However, non-perennial rivers and streams are usually unmonitored and often lack protection and adequate management. There is a clear need to study the hydrology, biogeochemistry and ecology of natural intermittent and ephemeral streams to characterize their flow regimes, to understand the main origins of intermittence and how this affects biogeochemistry and biodiversity, and to assess the consequences of altered flow intermittence due to climate change or other anthropogenic impacts.
This session welcomes all contributions on the science and management of non-perennial streams, and particularly those highlighting:
· current advances and approaches in monitoring and modelling flow intermittence,
· the effects of flow in non-perennial streams on downstream perennial stream water quantity and quality,
· the factors that affect the dynamics of the flowing stream network,
· land use and climate change impacts on flow intermittence,
· links between flow intermittence and biogeochemistry and/or ecology.
· public perceptions (and natural capital/ecosystem services) of non-perennial rivers,
· approaches to determine reference conditions on non-perennial rivers.

Convener: Ilja van Meerveld | Co-conveners: Nicola DurighettoECSECS, Mirjam SchellerECSECS, Catherine Sefton, E. Sauquet

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

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

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

Convener: Lionel Jarlan | Co-conveners: María José PoloECSECS, Mehrez Zribi, Said Khabba, Yves Tramblay

The Amazon River basin, the largest river system in the world, has long been under substantial environmental changes. However, recent decades have seen an accelerated pace of transformations driven mostly by anthropogenic pressures. Global climate change, combined with deforestation, forest degradation, and large infrastructures such as dams, has led to changes in its river system, affecting various components of the hydrological cycle such as precipitation, evapotranspiration, and river flow. These modifications affect the pulse of the rivers and wetlands, altering seasonal patterns of flooding and impacting several ecosystem functions. Climatic extremes have also been reported to be more frequent and more intense in the last decades, with floods and major droughts imposing hazardous conditions on local people. However, consequences are not only local: the basin harbors the largest tropical rainforest in the world and it is one of the main freshwater sources to the oceans. Changes in this large and complex system, therefore, affect the global climate as well as the hydrosphere, hence being of global concern.

In this session, we invite novel contributions from Hydrology and Hydroclimatology that help us uncover, debate, and update our knowledge about the most recent changes the Amazon River basin has been exposed to. Our aim is to create a productive debate that pushes forward the fundamental research that is needed to support the conservation of this important basin and its freshwater ecosystems.

Co-organized by BG4
Convener: Letícia Santos de LimaECSECS | Co-conveners: Ayan FleischmannECSECS, Jamil Alexandre Ayach AnacheECSECS, Marcia N. Macedo
HS2.1.4 EDI

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 fresh water supply. A considerable part of the world’s population depends on this water supply, around 26% live directly in the mountains and 40% live downstream of rivers originating in the mountains. The large elevation ranges and the heterogeneity of elevation-dependent hydro-meteorological conditions make mountains particularly sensitive to climate variability and change, but therefore also unique areas for identifying and monitoring the effects of global change.
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 hydrological conditions (in either mountain surface and/or ground water systems).
• Methods for differentiating climatic and anthropogenic drivers of hydrological change in the mountains.
• Modelling approaches to assess mountain hydrological change.
• Evolution, forecasting and impacts of extreme events.
• Case studies on adaptation to changing mountain water resources availability.

Solicited authors:
Walter Immerzeel
Convener: Marit Van TielECSECS | Co-conveners: Andrea MomblanchECSECS, David Haro Monteagudo, Daniel Viviroli
HS2.1.5 EDI

Water is the main critical factor for life in drylands. Dryland ecosystems and their inhabitants strongly rely on the scarce and often intermittent water availability in these regions. Drylands' characteristics increase the vulnerability to climate change and the susceptibility to the impact of short- to long-term extreme events and processes, such as floods, droughts, and desertification. These events can reshape the landscape through the mobilisation of surface sediments and forming sedimentary deposits, which preserve and allow the reconstruction of past states of the Earth's system, including changes in the extent of deserts. Nevertheless, the study of hydroclimatic processes in drylands remains at the periphery of many geoscientific fields. A proper understanding of the hydrological, hydrometeorological and (paleo)climatic processes in these regions is a cornerstone to achieve the proposed sustainable development goals we set for the end of this century.

This session welcomes contributions from scientific disciplines addressing any of the drylands' full range of environmental and water-related processes. The purpose is to foster interdisciplinary research and expand knowledge and methods established in individual subdisciplines.

Co-organized by AS1/CL2/GM7/NH1
Convener: Moshe ArmonECSECS | Co-conveners: Andries Jan De VriesECSECS, Pedro AlencarECSECS, Kathryn Fitzsimmons, Rodolfo NóbregaECSECS
HS2.1.6 EDI

Latin America is home to unique hydrological systems with some of the largest basins in the world. The combination of diverse climates, biomes, and ecosystems with rapidly growing human footprints caused by urbanization, population growth, and land use changes, among others, makes it necessary and urgent to explore hydrological knowledge at the interface of science, policy, and practice in water resources.
This session welcomes both theoretical and case study applications that consider observation and/or modelling to study hydrological processes and the possible effects of social and environmental changes such as deforestation, agricultural practices, climate variability and change, and pollution on water resources systems. We will explore advances in the science of hydrology at regional, national and continental scales in Latin America.
Aligned with the IAHS Scientific Decade HELPING (Hydrology Engaging Local People IN one Global world), we especially welcome contributions that: (1) investigate interactions of water resources across different spatial scales, (2) provide holistic solutions for water security, (3) engage with hydrological knowledge co-creation.
We want to discuss how science could improve operational hydrology, how practical problems can inform important scientific questions, and the skills and tools necessary for translating hydrological research into operation and decision-making in managing water resources systems of Latin America.

Convener: Pedro Luiz Borges Chaffe | Co-conveners: Mariana Madruga de BritoECSECS, James McPhee, Rodrigo Cauduro Dias de Paiva, Graciela Herrera Zamarrón
HS2.1.7 EDI

Since the last century, there has been a decrease in the water quality of lakes and reservoirs worldwide because of multiple stressors such as climate change, increased demand for water abstraction, and high nutrient levels caused by agricultural expansion and point sources. To quantify the streamflow response to multiple stressors at the catchment scale and compare the performance of hydrological models forced by reanalysis weather data and local weather data, applied to the groundwater-dominated Gudenå catchment in Denmark.
This talk outlines our challenges when setting up and calibrating SWAT+ in a groundwater-dominated catchment and discusses possible solutions.

Co-sponsored by AGU and YHS
Convener: anandita agarwalECSECS | Co-conveners: Alejandro GómezECSECS, Faluku NakulopaECSECS, Katrin Bieger
HS2.1.8 EDI

Due to a warming climate, mountain glaciers around the world are rapidly receding, shifting the predominant dynamics of the mountain cryosphere from glacial to periglacial. Permafrost is a central element of periglacial environments and, although it is warming and degrading on a global scale, there is an increasing proportion of permafrost subsurface ice compared to glacier surface ice, due to their different response times to atmospheric changes. However, relatively little is known about the hydrological, chemical and ecological conditions of mountain freshwaters influenced by permafrost, since glacier related systems have so far been the focus of scientific research.

Altered thermal conditions of the subsurface may affect water pathways, resulting in modified hydrological regimes associated with changes to recharge, storage and release processes, which are all related to melting ground‐ice. Permafrost degradation and the resultant changes in rock glaciers - and other mountain landforms - may partially offset water shortages (caused by the loss of glacial meltwater) by increasing the underground water storage capacity of mountain terrains due to the increase in the unfrozen sediment thickness. Observed changes associated with permafrost degradation include an increase in dissolved solutes (including nutrients, ions and heavy metals) in mountain waters, with potential effects on aquatic ecology. Yet, ice‐rich landforms such as rock glaciers are emerging as potential climate refugia because the slow loss of their subsurface ice enables the persistence of cold habitats and related biodiversity.

In this session, we encourage presentations about hydrology, chemistry, and ecology of mountain freshwaters in permafrost environments. Contributions addressing the following topics are welcome:
- Impact of permafrost degradation and ice loss on subsurface flow paths and runoff dynamics
- Influence of rock glaciers and other ice-rich mountain landforms on the hydrology and hydrochemistry of surface waters
- Role of permafrost degradation and related ice melt as a source of water
- Weathering processes and solute release in changing permafrost environments
- Hydrological and hydrochemical modelling of transitional glacial-periglacial catchments under ongoing climate change
- Biodiversity and adaptations of ecological communities dwelling permafrost-influenced surface waters

Convener: Nicola ColomboECSECS | Co-conveners: Thomas Wagner, Cassandra KoenigECSECS, Masaki Hayashi, Monica Tolotti
HS2.1.9 EDI

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.

Solicited authors:
S. McKenzie Skiles
Co-organized by CR2
Convener: Francesco Avanzi | Co-conveners: Giulia MazzottiECSECS, Guillaume Thirel, Abror Gafurov, Doris Duethmann
HS2.1.10 EDI

The African continent is experiencing various impacts of climate induced sequential droughts, floods, heatwaves, and alteration between two extremes. These changes are causing water and food insecurity in the region. The advances seen in hydrological models in better reproductions of observed variables such as streamflow and water availability are improving predictions of socio-economic risks of floods, droughts, and water stress. However, in data-sparse regions the use of hydroclimatic models for disaster risk reductions still requires improvement.

This session aims to bring together communities working on different strands of African hydrology, climate risks, water and food security, and environmental risks. We welcome both fundamental and applied research in the areas of hydrological process understanding, monitoring, drought/flood forecasting and mapping, seasonal forecasting, water resources management, climate impact assessment and societal implications. Interdisciplinary studies that combine the physical drivers of water-related risks and their socio-economic impacts in Africa are encouraged. Case studies showcasing practical innovative solutions relevant for decision making under large uncertainty are welcomed.

Convener: Meron Teferi Taye | Co-conveners: Moctar DembéléECSECS, Fiachra O'Loughlin
HS2.1.11 EDI

Forests are primary regulators of water, energy, and carbon cycles. Maintaining forest functional integrity is fundamental to the sustainability of ecosystems, societies, and human development as described in the UN Sustainable Development Goals.
Global change and anthropogenic intervention are putting enormous pressure on forests, affecting the ecosystem services they provide through water quantity and quality, and biogeochemical cycles. The conventional wisdom that forest hydrology emphasizes the role of forests and forest management practices on runoff generation and water quality has expanded in light of rapid global change. Some of the largest pristine forest areas are in the tropics and have undergone drastic changes in land use in recent decades. Although novel modeling and observational techniques have been applied as alternatives to develop cutting-edge research, these tropical systems remain notably underrepresented in hydrological studies compared to temperate regions, especially concerning long-term experimental setups and monitoring networks.
Improving our understanding of how hydrological processes in forest ecosystems are determined by time-invariant factors and time-varying controls, as well as how forested catchments respond to dynamic environmental conditions and disturbances, will depend critically on understanding forest-water interactions. Building this knowledge requires interdisciplinary approaches in combination with new monitoring methods and modeling efforts.
This session brings together studies that will improve our understanding of water-forest interactions and stimulate debate on the impact of global change on hydrological processes in forest ecosystems at different scales.
We invite field experimentalists and modelers working in forests from boreal to tropical regions to submit contributions that:
1) Improve our understanding of forest (eco)hydrological processes using an experimental or modeling approach or a combination of both;
2) Assess the hydrology-related impacts of land use/cover change and environmental disturbances on forested ecosystems;
3) Feature innovative methods and observational techniques, such as optical sensors, tracer-based experiments, monitoring networks, citizen science, and drones, that reveal new insights or data sources in forest hydrology;
4) Include interdisciplinary research that supports consideration of overlooked soil-plant-atmosphere components in hydrological studies.

Convener: Daniele Penna | Co-conveners: Luisa Hopp, Rodolfo NóbregaECSECS, Alicia CorreaECSECS

The Critical Zone (CZ) – the permeable near-surface layer of the Earth where the lithosphere, hydrosphere, atmosphere, and biosphere interact – is the place where cycles of carbon, nutrients, water and other biogeochemical processes intersect with ecosystems and society. Investigating the form and functioning of the CZ requires that insights from geology, hydrology, ecology, geochemistry, atmospheric science and other disciplines are integrated in a transdisciplinary manner. One successful approach to CZ research has been the development of intensively instrumented study areas, known as CZ observatories. The experimental design and management of these observatories are aimed specifically at interdisciplinary research. More recently, networks of observatories and interlinked thematically-focused projects have evolved to capitalize on advances possible through multifaceted collaborations across larger spatial scales. This session will highlight the cutting edge of CZ science at the project, observatory, and network levels. Submissions are solicited that focus on integration of observations and modeling; hydrologic dynamics; geoecological interactions; biogeomorphology, mineral weathering and nutrient cycling; the rhizosphere; the societal relevance of CZ science; and other examples of how CZ research is evolving with new knowledge to face the challenges of our changing world. Contributions from early-career scientists are particularly encouraged.

Co-organized by BG3/GM5/SSS5
Convener: Jeffrey Munroe | Co-conveners: Bhavna Arora, Theresa Blume, Sylvain Kuppel

HS2.2 – From observations to concepts to models (in catchment hydrology)

Sub-Programme Group Scientific Officers: Björn Guse, Miriam Glendell

HS2.2.1 EDI

Stable and radioactive isotopes as well as other natural and artificial tracers are useful tools (i) to fingerprint the sources of water and solutes in catchments, (ii) to trace flow pathways or (iii) to quantify exchanges of water, solutes and particulates between hydrological compartments. We invite contributions that demonstrate novel applications and recent developments of isotope and other tracer techniques in hydrological field studies and modelling in the areas of surface water-groundwater interactions, unsaturated and saturated zone, rainfall-runoff processes, cold-region hydrology, nutrient or contaminant transport, ecohydrology or other catchment processes.

Solicited authors:
Hjalmar Laudon
Convener: Pertti Ala-aho | Co-conveners: Andrea PoppECSECS, Michael Stockinger, Christine Stumpp
HS2.2.2 EDI

Significant advance in the understanding of water transit times, subsurface structure controls on biogeochemical reactions, and the quantification of catchment scale weathering rates have resulted in the convergence of biogeochemical and hydrological frameworks. Although such convergence is necessary for a mechanistic understanding of the Critical Zone, many challenges still exist. Perhaps the most difficult of all is to reach a unifying hydro-biogeochemical theory that can compare catchments across gradients of climate, geology, and vegetation. Understanding the processes driving the evolution of chemical tracers as they move through space and time is of cardinal importance to validating hypotheses regarding Critical Zone features such as the residence time of water in catchments, concentration-discharge relationships, or nutrient cycling through ecosystems. This session aims to initiate and/or intensify exchanges between two of the main scientific fields in Critical Zone science: hydrology and geochemistry. We are expecting novel approaches that allow merging hydrological modelling with studies of biogeochemical processes.

Convener: Christophe Hissler | Co-conveners: Markus Hrachowitz, Julien Bouchez, Erwin Zehe, Sofía López UrzúaECSECS
HS2.2.3 EDI

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.

Convener: Elham R. Freund | Co-conveners: Simon Stisen, Björn Guse, Luis Samaniego, Sina KhatamiECSECS
HS2.2.4 EDI

A survey of the current state-of-the-art in Earth System Science indicates that currently high-resolution reanalyses of essential terrestrial climate variables primarily serve sector-specific needs (e.g., atmospheric, oceanic, land surface, hydrological, or terrestrial carbon cycle reanalysis). Integration among land surface, hydrology, biota, and carbon processes still needs to be improved. The primary cause for this deficiency is the substantial computational costs inherent in Earth modeling systems and their assimilation algorithms. For example, when producing regional or continental-level streamflow reconstitution, Earth Observation (EO) inputs are typically underutilised or entirely absent.

Large-scale, high-resolution (1 km, 1 day) simulations of the water cycle can be developed through a systematic integration of EO retrieval systems and land surface\hydrological modelling. We need to foster the collaboration between hydrological modellers and EO scientists communities by connecting their expertise to enable credible estimates of water cycle components via hyper-resolution Earth observations and land-surface modelling. Hydrologists should not merely utilise satellite data as an end-user without providing feedback to remote sensing scientists. Conversely, EO scientists should consider the feedback and criticism of hydrologists.

This session aims to unite both communities and encourage submissions relating to the following topics:
- Develop reliable methods and approaches for the validation of EO products and modelling simulations with a specific focus on the high resolution.
- Improving the integration of EO products and modelling by ensuring consistency in terms of ancillary information and (more challenging) process representation.
- Addressing the intrinsic uncertainties in EO products and in meteorological\hydrological simulations—and their relative scales—to provide improved predictability of the different components of the water cycle.
- Improving the parameterization of the land surface processes through the integration of EO products.
- Addressing the human impact on the water cycle through advanced methods of integration of EO products into modelling.

Convener: Almudena García-GarcíaECSECS | Co-conveners: Bram DroppersECSECS, Pietro StradiottiECSECS, Luca Brocca, Luis Samaniego
HS2.2.5 EDI

A multitude of processes contribute to the hydrologic functioning of catchments. Traditionally, catchment hydrology has been centered around surface runoff, which is readily observable. But at the same time, invisible below ground processes entailing the storage dynamics and flows of water are still underexplored. This includes subsurface runoff, as well as feedbacks of subsurface processes to the surface and the specific role of soil moisture in shaping these fluxes. This session aims to bring together contributions on the following topics and to address gaps in observations, models, and understanding of hydrologic systems:

- Identifying, tracing, and modeling subsurface runoff generation at the catchment scale.

- Factors and mechanisms controlling subsurface water storage and fluxes

- How soil moisture measurements at different scales can be used to improve process understanding, models, and hydrologic theory

- Interactions of surface and subsurface hydrologic processes

Convener: Peter Chifflard | Co-conveners: Theresa Blume, Katya Dimitrova PetrovaECSECS, Josie Geris, Daniele Penna
HS2.2.6 EDI

Large data samples of diverse catchments provide insights into the physiographic and hydroclimatic factors that shape hydrological processes. Such data sets enable research on 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 that advance the characterization, organisation, 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?
2. Catchment similarity and regionalization: Can currently available global datasets be used to define hydrologic similarity? How can information be transferred between catchments and to data-scarce regions?
3. Modelling capabilities: How can we improve process-based and machine learning modelling by using large samples of catchments?
4. Testing of hydrologic theories: How can we use large samples of catchments to test and refine hydrologic theories and asses their general validity?
5. Identification and characterisation 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 (systematically) represent human influences in large sample datasets and use them to infer hydrological response under changing environmental conditions?

Convener: Nans Addor | Co-conveners: Sarah HanusECSECS, Sara LinderssonECSECS, Saskia SalweyECSECS, Wouter KnobenECSECS

Water transit times are proxies for various hydrological and biogeochemical processes within catchments. The aim of the session is to present studies that investigate transit time dynamics purely experimentally or via data and/or model driven approaches (like, e.g., tracer-aided modeling). We encourage presentations of new experimental and modeling methods to determine and explore transit times, appreciate contributions that link biological and geochemical processes with transit times and also welcome research on many other aspects of water ages, such as:
• What controls transit time dynamics at the catchment scale?
• How do transit times differ between different flowpaths and fluxes?
• How does transit time influence hydrochemical response?
• Can we improve (reactive) transport modeling using transit times?
• What are the uncertainties in transit-time modelling and how can we deal with them?

Solicited author:

Convener: Ingo Heidbüchel | Co-convener: Tamara Kolbe
HS2.2.8 EDI

Hydrologists can seek simplicity in universal laws, or revel in complex place- and purpose-specific models and measurements. Advancements in hydrology likely require a synthesis of both perspectives. New insights can originate both from detailed site-specific applications, or from studies that use large datasets and/or models to find generalizable hydrologic insights. This session is intended to provide a discussion platform in the search for generalizable insights in hydrology and, ideally, to help bridge the gap between local site-specific insights and more general hydrologic theories.

We welcome a broad range of contributions that could, for example, focus on:
(1) Improved process understanding or discovery of new processes through field and modeling applications
(2) Systematic understanding of hydrologic behavior across spatio-temporal scales as well as climatic and/or biophysical gradients
(3) The identification and use of patterns in large datasets to develop theories and models
(4) Leveraging process understanding from (small-scale) experimental studies and theories to build or constrain (large-scale) models
(5) Development or application of (physics-guided) machine learning methods to extract more information from available observations
(6) Approaches that provide causal or mechanistic explanations for observed patterns
(7) Understanding new aspects of hydrologic functioning by coupling hydrologic, geomorphic, ecologic, atmospheric, and/or human systems

Invited speaker: David Litwin (GFZ Potsdam)

Solicited authors:
David Litwin
Convener: Sebastian GnannECSECS | Co-conveners: Wouter BerghuijsECSECS, Sara BonettiECSECS

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 underline 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 methods 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 river flow methods and which link innovative research to operational monitoring.

Co-organized by GM11
Convener: Nick Everard | Co-conveners: Alexandre Hauet, Anette EltnerECSECS, Silvano F. Dal Sasso, Alonso PizarroECSECS
HS2.2.10 EDI

In the last decades, agro-ecosystems (i.e., arable land and grassland, orchards, forest, agro-forestry, urban fabric) have been significantly impacted by unfavorable extreme occurrences induced by global warming like floods and droughts, which have detrimental effects on the environment, the economy, and society. Optimal management of water resources requires reliable scenario-based modelling approaches to sustain appropriate, quick-response, and cost-effective adaptation options. The prediction performance of process-oriented eco-hydrological models is largely reliant on the quantity and quality of input data. The rapid technological advancement and integration of next-generation sensors (from ground-based to remote-based) has already revolutionized hydrological science and may improve the performance of model predictions from plot to catchment scale and beyond. Ultimately, hydrology entered the era of big data, machine learning, the Internet of Things, and digital twins. Therefore, we strive for concerted and dedicated action in the field of hydrology to harmonize hydrological data retrieval, encourage the design of cross-catchment experiments, and facilitate the scientific community’s access to the associated data. The following subjects will be covered to address these topics:
• New-generation sensor networks to monitor and track state variables, water fluxes, and understand the interactions and feedbacks between surface and groundwater interfaces over different spatial scales (from plot to catchment scale);
• Development of reliable modelling approaches to predict state variables, water fluxes at various spatial scales under extreme and adverse projected climate conditions;
• Development of ecosystem vulnerability and resilience indicators;
• Initiatives to build extensive research infrastructure networks to exploit the most recent hydrology discoveries.

Convener: Paolo Nasta | Co-conveners: Heye Bogena, Isabelle Braud, Roland Baatz

HS2.3 – Water quality at the catchment scale

Sub-Programme Group Scientific Officers: Björn Guse, Miriam Glendell

HS2.3.1 EDI

Surface water quality is typically assessed and managed at the catchment scale. To be effective, management decisions require sound process knowledge and an understanding of the underlying cause-and-effect relationships. However, the dynamics of solute and particulate concentrations integrate a multitude of hydrologic and biogeochemical processes that interact at different temporal and spatial scales and are difficult to assess with local field experiments. Therefore, data-driven statistical analysis of discharge and concentration time series at the outlet of a catchment can help illuminating the underlying processes. Long-term, high-frequency, as well as multiple-site data sets can serve as the basis for experimental and modeling studies. They can also be used to formulate and test hypotheses on dominant ecohydrological and geochemical processes moving “from pattern to process”.
Recent advances in this field include:
- The use of concentration-discharge relationships to understand the interplay between hydrologic and biogeochemical controls, both in the terrestrial part of catchments and in the river network.
- The use of long-term time series of nutrient input-output relationships to understand the effects of nutrient legacies and catchments' response times.
- High-frequency observations to understand the fine structure of concentration dynamics, including flow paths, their age distribution during runoff events, and ecological controls on diurnal cycles.

The goal of this session is to bring together studies that use statistical analysis of river concentration time series to draw conclusions about solute and particulate mobilization, retention, and export mechanisms. Presentations on the following topics are encouraged:

- Insights from observational data analysis to build conceptual and process-based models
- Interpretation of concentration-discharge relationships from a range of temporal scales
- Use of high-frequency water quality observations
- Long-term trajectories in nutrient inputs, outputs, and nutrient stoichiometry
- Role of climate change and hydrologic extremes in altering nutrient export patterns
- Instream, network and lake effects on the dynamics of nutrient loads and concentrations
- Relationship between water travel times and the dynamics of water quality

Convener: Andreas Musolff | Co-conveners: Carolin Winter, Rémi Dupas, Camille VaultierECSECS, Anna Lintern

Quantifying different aspects of uncertainty in model prediction has become an integral part of good modelling practice. To this end Bayesian and other probabilististic approaches and artificial intelligence algorithms are increasingly popular in water quality modelling for supporting environmental decision making. Ideally, these models enable consideration of prediction reliability, relating uncertainties to a decision makers’ risk attitudes and preferences, all while accounting for the uncertainty related to our system understanding, data and random processes. Bayesian modelling, including graphical Bayesian Belief Networks, hierarchical models, ‘hybrid’ mechanistic/data-driven models as well as a range of machine-learning approaches, are increasingly used as powerful decision support tools for water quality management and assessment, facilitating stakeholder engagement in the model building process and allowing for adaptive management within an uncertainty framework.

This session aims to review the state-of-the-art advances and applications in the field of probabilistic, machine-learning and hybrid water quality modelling approaches, within both frequentist and Bayesian paradigms, and their utility in supporting decision-making.

We seek contributions, for example, but not exclusively, that apply water quality modelling approaches to:
• quantify the uncertainty of model predictions (due to data, model structure and parameter uncertainty)
• interpret and characterize uncertainties in machine-learning and data mining approaches that learn from large, possibly high-resolution data sets
• address the problem of scaling (e.g. disparity of scales between processes, observations, model resolution and predictions)
• test model transferability and generalisability of findings
• model water quality in either data-rich or data-sparse environments
• involve stakeholders in model development and maximise the use of expert knowledge to inform risk analysis and decision support, incl. monitoring, reporting and catchment management

Convener: Miriam Glendell | Co-conveners: Danlu GuoECSECS, Daniel Obenour, Stefano Basso, David C. Finger
HS2.3.3 EDI

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 need 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 with aquatic ecology.
Models can help to optimize monitoring schemes and provide assessments of future changes and management options. However, insufficient temporal and/or spatial resolution, a short duration of observations and the widespread use of different analytical methods limit the potential 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. In addition, models should be capable of representing changing land use and climate conditions to meet the needs of decision makers under uncertain future conditions Given these challenges, there remains a strong need for advances in water quality modeling.

This session aims to bring together scientists working on both experimental and modelling studies to improve the prediction and management of water quality constituents (e.g. nutrients, organic matter, algae, sediment) at the catchment scale. Contributions addressing the following topics are welcome:

- 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 effective water quality monitoring schemes
- Innovative monitoring strategies that support both process investigation and improved model performance
- Advanced modelling tools for integrating catchments and/or simulating in-stream processes
- Observational and modelling studies at the 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

Convener: Paul Wagner | Co-conveners: Sarah Halliday, Daniel HawtreeECSECS, Nicola Fohrer

The enrichment of ecosystems with nutrients and other contaminants is strongly impairing the recreational, industrial, and ecological functions of water resources around the world. Anthropogenic activities like agriculture and wastewater discharge have resulted in the degradation of groundwater and surface water quality with severe implications for both human and environmental health. Together with the Water Framework Directive deadline of 2027 coming up soon, it is of vital importance to reduce the impact of agriculture on water quality. At the same time the agricultural sector is required to become increasingly productive due to global population growth, which without changing land use practices will further increase its pressure on downstream ecosystems. There are many options to reduce agricultural nutrient losses, but the implementation of measures requires the commitment of many stakeholders. Furthermore, next to (cost-)effectiveness also robustness and user friendliness are essential for acceptance. The effect of a certain measure may also be hampered by local climatic and hydrochemical conditions.
This session invites studies on mitigation measures and other solutions to decrease nutrient loading as well as studies on nutrient dynamics in agricultural catchments. We strongly encourage to share both best practices in mitigation measures as well as innovative measures which are under development or tested under lab-scale conditions. Also, catchment modeling with the aim of optimizing the placement of mitigation measures and prevent shadowing effects are encouraged.

Convener: Inge van DriezumECSECS | Co-conveners: Joachim Rozemeijer, Brian Kronvang, Katrin Bieger, Daniel Graeber
HS2.3.5 EDI

Plastic pollution in freshwater systems is a widely recognized global problem with potential environmental risks to water quality, biota and livelihoods. 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.

This session welcomes contributions from field, laboratory and modelling studies that aim to advance our understanding of river network and catchment-scale plastic transport and accumulation processes. We are soliciting studies dedicated to all plastic sizes (macro, micro, nano) and across all geographic settings. We are especially encouraging studies that can link plastic accumulation and transport to catchment-wide hydrological, ecological or geomorphological processes that we can better understand where, when and why plastics accumulation takes place in aquatic-terrestrial environments.

In this session, we explore the current state of knowledge and activities on macro-, micro- and nanoplastics in freshwater systems, focusing on aspects such as:

• Transport processes of plastics at catchment scale;
• 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);
• Plastic in rivers, lakes, urban water systems, floodplains, estuaries, freshwater biota;
• Effects of hydrological extremes, e.g. accumulation of plastics during droughts, and short-term export during floods in the catchment;
• Modelling approaches for global river output estimations;
• Legislative/regulatory efforts, such as monitoring programs and measures against plastic pollution in freshwater systems.

Convener: Louise SchreyersECSECS | Co-conveners: Daniel González-Fernández, Marcel Liedermann, Freija MendrikECSECS, Paul VriendECSECS
HS2.3.6 EDI

Aquatic ecosystems and the services they provide are increasingly threatened by impaired water quality arising from multiple pressures, including climate and land-use change. In areas experiencing agricultural intensification, the increasing application of inorganic fertiliser, coupled with climate-induced changes to nutrient cycling and runoff generation, can result in the eutrophication of receiving waters, including rivers, lakes and the marine environment. Sources of nutrients, along with other pollutants such as E. coli, may be further enhanced through increases in livestock densities. Such issues particularly affect middle-income tropical countries where growing populations and the need for food security are driving a transition from traditional farming methods to more intensive forms of agriculture.

Effectively mitigating agricultural water pollution whilst simultaneously limiting the impact on productivity requires sound knowledge of the sources and pathways of pollutants in time and space. This will likely be achieved through the integration of data and models to produce decision support tools that are useful and used by those responsible for water management. However, many existing water quality models lack the fine spatial discretisation necessary to inform localised targeting of mitigation measures. In addition, many tropical catchments suffer from infrequent monitoring of water quality due to limited funding and lack of expertise, reducing the potential for model-data fusion.

The aim of this session is to bring together scientists exploring novel approaches to water quality monitoring and modelling that can provide a robust understanding of agricultural pollutant sources and pathways in time and space. The main focus will be on the tropics, however contributions from other environments that are transferable can be considered. Example topics for contributions include:

• Opportunities and challenges for enhancing data collection in data-sparse environments,
• Low-cost technologies for water quality monitoring,
• GIS-based models or models with minimal information requirements,
• Process-based modelling and approaches to uncertainty estimation and/or reduction,
• Translation of research models into decision support tools.

Convener: Aaron NeillECSECS | Co-conveners: Suzanne JacobsECSECS, Christian Birkel, Frank Masese, Sim Reaney
HS2.3.7 EDI

A large number of pathogens, micropollutants and their transformation products (veterinary and human pharmaceuticals, pesticides and biocides, personal care products, organic pollutants (e.g. PFAS) and heavy metals, chlorinated compounds) 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 programs 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 groundwater 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 such as new detection methods for DNA, pathogens, micropollutants, non-target screening
- Experimental studies to improve process understanding and to quantify diffuse and point source inputs
- Biogeochemical interactions and impact on micropollutant behaviour
- Comparative fate studies on parent compounds and transformation products
- Biogeochemical interactions and impact on micropollutant behaviour
- Modelling approaches (including hydrology and sediment transport) to simulate pollutant transport and fate at several spatial and temporal scales
- Modelling tools for decision support
- Setup of mitigation measures and evaluating their effectiveness.
- Methods to evaluate water quality modelling uncertainty, and/or combining data and modeling (data assimilation)

Convener: Matthias Gassmann | Co-conveners: Shulamit NussboimECSECS, Felicia LinkeECSECS, Poornima NageshECSECS, Claire Lauvernet
HS2.3.8 EDI

The occurrence of pathogens and of 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, antibiotic resistance bacteria) are introduced into surface water through the direct discharge of wastewater, by the release from animal manure or animal waste via overland flow, or, into groundwater through the transport from soil, 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, as discharges from wastewater treatment plants (e.g., trace organic contaminants, PFAS), or occur due to microbial growth (e.g. cyanotoxins), posing a burden on human health. 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.

This session aims to increase the understanding about the dominant processes controlling fecal indicator, pathogen and contaminant fate and transport at larger scales. Consequently, we welcome contributions that aim to close existing knowledge gaps and include both small and large-scale experiments, with the focus on
- the fate and transport of fecal indicators, pathogens, emerging contaminants including persistent and mobile organic trace substances (e.g. antibiotic resistance bacteria, cyanotoxins, PFAS) in rivers, soils, groundwater and estuaries
- Hydrological, physically based modelling approaches
- Methods for identifying the dominant processes and for transferring transport parameters of fecal indicators, pathogens and contaminants 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

Solicited authors:
Scott Alan Bradford
Convener: Julia Derx | Co-conveners: Sondra Klitzke, Margaret StevensonECSECS, Fulvio Boano, Yakov Pachepsky

HS2.4 – Hydrologic variability and change at multiple scales

Sub-Programme Group Scientific Officers: Björn Guse, Miriam Glendell


The space-time dynamics of floods are controlled by atmospheric, catchment, riverine and anthropogenic processes, and their interactions. The natural oscillation between flood-rich and flood-poor periods is superimposed on anthropogenic climate change and human interventions in river morphology, water retention capacity and land use. In addition, flood risk is further shaped by continuous changes in exposure and vulnerability. In this complex setting, it remains unclear what is the relative contribution of each factor to the space-time dynamics of flood risk. The scope of this session is to report when, where, how (detection) and why (attribution) changes in the space-time dynamics of floods occur. The session particularly welcomes presentations on attributing different drivers to observed changes in flood risk. Presentations on the impact of climate variability and change, land use transitions, morphologic changes in streams, and the role of pre-flood catchment conditions in shaping flood risk are welcome as well. Furthermore, contributions on the impact of socio-economic factors, including adaptation and mitigation of past and future risk changes are invited. The session will further stimulate scientific discussion on detection and attribution of flood risk change. Specifically, the following topics are of interest for this session:

- Long-term changes in rainfall patterns and flood occurrence;
- Process-informed extreme value statistics;
- Interactions between rainfall distribution and catchment conditions in shaping flood patterns;
- Detection and attribution of flood hazard changes, such as atmospheric drivers, land use controls, natural water retention measures, and river training;
- Changes in flood exposure: economic and demographic growth, urbanisation of flood prone areas, implementation of multi-scale risk mitigation measures (particularly structural defences);
- Changes in flood vulnerability: changes of economic, societal and technological aspects driving flood vulnerability and private precautionary measures;
- Multi-factor decomposition of observed flood damages combining the hydrological and socio-economic drivers;
- Future flood risk scenarios and the role of adaptation and mitigation strategies.

Convener: Dominik PaprotnyECSECS | Co-conveners: Miriam BertolaECSECS, Marco Lompi, Nivedita Sairam, Larisa Tarasova
HS2.4.2 EDI

Assessing the impact of climate variability and changes on hydrological systems and water resources is crucial for society to better adapt to future changes 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. From one model to another, or from a single model realization to another, the impact of diverging trends and sequences of interannual and decadal variability of various internal/natural climate modes (e.g., ENSO, NAO, AMO) could substantially alter the impact of human-induced climate change on hydrological variability and extremes. Therefore, we need to improve both our understanding of how internal/natural climate patterns affect hydrological variability and extremes, and how we communicate these impacts. We also need to better understand how internal/natural variations interact with various catchment properties (e.g., vegetation cover, groundwater support) and land-use changes altering them. In this direction, storylines of plausible worst cases, or multiple physically plausible cases, arising from internal climate variability can complement information from probabilistic impact scenarios.

We welcome abstracts capturing recent insights for understanding past or future impacts of internal/natural climate variability on hydrological systems and extremes, as well as newly developed probabilistic and storyline impact scenarios. Results from model intercomparisons using large ensembles are encouraged.

Solicited authors:
Theodore Shepherd
Co-organized by CL4/NH1
Convener: Bastien Dieppois | Co-conveners: Hayley Fowler, Wilson ChanECSECS, Katie Facer-ChildsECSECS, Jean-Philippe Vidal
HS2.4.3 EDI

Hydrological extremes (floods and droughts) have major impacts on society and ecosystems and are projected to increase in frequency and severity with climate change. These events at opposite ends of the hydrological spectrum are governed by different processes that operate on different spatial and temporal scales and require different approaches and indices to characterize them. However, there are also many similarities and links between the two types of extremes which 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 improve the understanding of the processes governing both types of hydrological extremes, develop robust methods for modelling and analyzing 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 analyses of flood or drought non-stationarity under the effects of climate-, land cover-, and other anthropogenic changes. Studies that investigate both extremes are of particular interest. We especially encourage submissions from early-career researchers.

Solicited authors:
Miriam Bertola,Anne Van Loon
Co-organized by NH1
Convener: Manuela Irene BrunnerECSECS | Co-conveners: Louise Slater, Gregor Laaha, Marlies H BarendrechtECSECS, Wouter BerghuijsECSECS
HS2.4.4 EDI

This session focusses on hydrological response to changes in climatic forcing at multi-annual to multi-decadal timescales. Catchments are immensely complex 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. Efforts to improve the realism of hydrological projections under future climate scenarios;
2. Better understanding of hydrological and/or biophysical processes related to long-timescale climate shifts potentially contributing to apparent shifts in hydrologic response;
3. Understanding and quantifying catchment multi-annual “memory”;
4. Studies that use, extend, or re-assess known hydrological regularities (e.g. the Budyko hypothesis) for predictions under changing conditions; and
5. Data-based and modelling studies aiming to better understand and simulate the response of hydrological systems to historic climatic variability and change.

Convener: Keirnan FowlerECSECS | Co-conveners: Doris Duethmann, Luca TrotterECSECS, Gabrielle BurnsECSECS

HS2.5 – Global and (sub)continental hydrology

Sub-Programme Group Scientific Officers: Björn Guse, Miriam Glendell

HS2.5.1 EDI

In the current context of global change, a better understanding of our large-scale hydrology is vital. For example, by increasing our knowledge of the climate system and water cycle, improve assessments of water resources in a changing environment, perform hydrological forecasting, and evaluate the impact of 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) the use of global earth observations and in-situ datasets for large-scale hydrology and data assimilation techniques for large-scale hydrological models;

(iii) representation and evaluation of various components of the terrestrial water cycle fluxes and storages (e.g., soil moisture, snow, groundwater, lakes, floodplains, evaporation, river discharge) and atmospheric modelling;

(iv) synthesis studies that combine knowledge gained at smaller scales (e.g. catchments or hillslope) to increase our knowledge on process understanding needed for further development of large-scale hydrological models and to identify large-scale patterns and trends.

Convener: Inge de GraafECSECS | Co-conveners: Ruud van der EntECSECS, David Hannah, Oldrich RakovecECSECS, Shannon Sterling
HS2.5.2 EDI

Groundwater provides about 40% of all human water abstractions and is an essential water source for terrestrial ecosystems and freshwater biota in rivers, lakes, and wetlands. Aquifers may span political and natural boundaries, but our large-scale understanding of groundwater processes and the connection between ground and surface waters is still limited.
The development of global groundwater models and big-data assessments of groundwater wells have helped to push the boundaries of our large-scale understanding of groundwater processes. In particular, knowledge of the exchange between surface and subsurface waters is essential for determining the water balance at larger scales. Surface and subsurface water exchanges and 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) increasingly affect groundwater flow processes and the exchange between surface and subsurface waters.
In this session, we want to highlight the increasing interest in the large-scale study of groundwater availability, quality, and processes (including groundwater recharge) and discuss current obstacles related to data availability and model design. Therefore, we seek contributions that address issues including:
• Regional to global groundwater-related datasets and big-data assessments
• Transboundary and inter-catchment assessments of groundwater processes
• Identification of dominant controls on groundwater processes across large domains
• Recent methodological developments for inclusion of small-scale hydrological processes into large-scale estimates
• Surface-subsurface water exchange and its effects on hydrological extremes (drought/flood), water availability, and solute and pollutant transport
• Effects of climate change, land use change, and water use change on global groundwater
• Implications of large-scale groundwater understanding on monitoring design, integrated water management, and global water policies
• Large-scale groundwater assessments related to the fulfillment of the UN sustainable development goals (SDGs)

Convener: Robert ReineckeECSECS | Co-conveners: Fanny SarrazinECSECS, Yan LiuECSECS, Sebastian GnannECSECS, Emmanuel DuboisECSECS