Anthropogenic activities, climate change and poor water resources management lead to insufficient water quality, both biological and chemical, and results in one of the world’s most urgent human health issues. Waterbodies are key for waterborne diseases and water surface water network for spreading of contaminants and diseases. The global health burden could be reduced by improving water supply, sanitation and management of water resources but also by improved understanding of the role of hydrology in transport of pathogens. This scientific session aims to explore the interdisciplinary facets of water cycle and human health in broad sense. By bringing together experts from hydrology, environmental pollution, microbiology, ecology, epidemiology and public health, this session seeks to foster a dialogue to effectively study hydrological processes related to spreading and transmission of diseases and emergent contaminants. The oral part of the session is composed of solicited presentations followed by a panel discussion.

Per- and polyfluoroalkyl substances (PFAS) are a group of man-made chemicals that have been extensively used worldwide for over 80 years due to their unique chemical properties, such as high stability and resistance to degradation. The widespread use of PFAS has led to pervasive contamination in terrestrial and aquatic environments, creating complex regulatory and environmental management challenges.

This session aims to contribute to a comprehensive understanding of PFAS pollution and to share effective strategies for their management and remediation/mitigation. Hence, we aim to bring together researchers and practitioners from diverse fields, including contaminant hydrogeology, environmental chemistry, toxicology, engineering, and policy, to share their insights on the occurrence, behaviour, and management of PFAS in the environment. We primarily seek contributions that explore the latest advancements in understanding PFAS pollution across different environmental matrices, including surface water, groundwater, and soils.

Topics of interest include, but are not limited to:
- The transport and fate of PFAS in terrestrial and aquatic environments,
- Modelling approaches to predict PFAS distribution and transport in various environmental settings,
- Innovative strategies and technologies for the treatment and remediation of PFAS-contaminated water, including drinking water and wastewater,
- Advancements and case studies on the successful application of PFAS remediation/mitigation techniques and their effectiveness in different environmental contexts,
- Ecotoxicological studies,
- Challenges and advancements in regulatory frameworks and policies for managing PFAS pollution, including approaches to identify and mitigate sources of PFAS contamination.

Given the complex nature of PFAS as "forever chemicals" and their ability to partition across different environmental media, this session emphasises the importance of interdisciplinary approaches and collaborative efforts to tackle the multifaceted challenges they present. We welcome studies that utilise laboratory research, field investigations, and modelling efforts, as well as contributions that discuss the implications of PFAS pollution on public and environmental health, ecological integrity, and regulatory landscapes.

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

Invited speaker: Prof. Gertjan Medema, KWR

This session is dedicated to the comprehensive investigation of small-scale transport processes governing the movement of plastics (ranging from micro- 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 numerical techniques, highlighting improvements in accuracy, complexity, and spatial-temporal resolution. Cutting-edge modeling 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.

This session is devoted to the study of fate and transport processes of micro and nanoplastic (MNP) particles in soil and groundwater systems. While MNPs in marine and aquatic environments have received considerable interest by the scientific community over the last decade, soil and groundwater environments are comparably understudied and MNP transport and fate in these compartments is less well understood.

We welcome contributions that provide a comprehensive overview on the problem of soil and groundwater MNP contamination from local to global scales. Additionally, we are looking forward to contributions around field sampling, lab processing and characterization techniques specific to MNP in soil and groundwater compartments, as well as to experiments and modelling studies that advance our theoretical understanding of how MNP as well as their leachtes interact with soil and groundwater ecosystems and influence their biochemistry.

With this session we strive to extend our knowledge on MNP fate, transport and interaction with soil and groundwater environments with a diverse range of hydrological and biochemical characteristics including soil type, grain size, hydraulic connectivity, flow velocity and groundwater recharge capacity, organic matter content and microbial activity or soil chemistry. We hope that a better understanding of MNP pathways through the subsurface will aid us in conceptualising potential exposure hazards and pollution risks of vital soil and groundwater resources.

Effective and enhanced hydrological monitoring is essential for understanding water-related processes in our rapidly changing world. Image-based river monitoring has proven to be a powerful tool, significantly improving data collection, analysis, and accuracy, while supporting timely decision-making. The integration of remote and proximal sensing technologies with citizen science and artificial intelligence has the potential to revolutionize monitoring practices. To advance this field, it is vital to assess the quality of current research and ongoing initiatives, identifying future trajectories for continued innovation.

We invite submissions focused on hydrological monitoring utilizing advanced technologies, such as remote sensing, AI, machine learning, Unmanned Aerial Systems (UAS), and various camera systems, in combination with citizen science. Topics of interest include, but are not limited to:

• Disruptive and Innovative sensors and technologies in hydrology.
• Advancing opportunistic sensing strategies in hydrology.
• Automated and semi-automated methods.
• Extraction and processing of water quality and river health parameters (e.g., turbidity, plastic transport, water depth, flow velocity).
• New approaches to long-term river monitoring (e.g., citizen science, camera systems—RGB/multispectral/hyperspectral, sensors, image processing, machine learning, data fusion).
• Innovative citizen science and crowd-based methods for monitoring hydrological extremes.
• Novel strategies to enhance the detail and accuracy of observations in remote areas or specific contexts.

The goal of this session is to bring together scientists working to advance hydrological monitoring, fostering a discussion on how to scale these innovations to larger applications.

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

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.

The interaction between the soil-plant-atmosphere compartments and human activities is of paramount importance for the sustainable management and preservation of ecosystem functions and services. The functionality and services of terrestrial ecosystems are threatened by global climate change and human activities. The complexity and comprehensiveness of the impacts have so far proven challenging to assess due to the limitations of simplified experimental approaches and long-term observations, which often focus on a limited number of response variables.
Experimental systems such as lysimeters or ecotrons provide continuous, high-resolution and high-quality observations of detailed time series, which are crucial for a more accurate determination of the Earth's ecosystem services and functions and for promoting interdisciplinary ecosystem research.
This session will mainly focus on the diversity of ecosystem research using research platforms of lysimeters and ecotrons. We would also like to address the challenges of modelling ecosystem processes, comparison of metrics with other in situ instruments, upscaling approaches from such platforms to larger scales, validation studies (e.g. remote sensing), but also new developments in the field of lysimetry and further development of processing algorithms for interpretation of high temporal resolution lysimeter/ecotron weight data. We welcome contributions that (1) present novelties in the field of lysimeters, (2) assess and compare the functioning and services of terrestrial ecosystems, particularly in relation to climate change, (3) focus on water and nutrient transport processes (4) and greenhouse gases within the soil-plant-atmosphere continuum, (5) develop new techniques for the analysis of lysimeter and ecotron observations, (6) include ecosystem or hydrological modelling approaches using in situ observations from lysimeters or ecotrons.

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, in-situ observational networks are increasingly inadequate when faced with extreme conditions, and lack the precision and spatial coverage to fully represent crucial aspects of the hydrological cycle.

This session aims to tackle this problem by inviting presentations that demonstrate new and improved methods and approaches to streamflow monitoring, including:
1) Innovative methodologies for measuring/modelling/estimating river stream flows;
2) Real-time acquisition of hydrological variables;
3) UAS and satellite remote sensing techniques for hydrological & morphological monitoring;
4) Measurement in extreme conditions associated with the changing climate;
5) Measurement of sudden-onset extreme flows associated with catastrophic events;
6) Strategies to quantify and describe hydro-morphological evolution of rivers;
7) New methods to cope with data-scarce environments;
8) Inter-comparison of innovative & classical models and approaches;
9) Evolution and refinement of existing methods;
10) Guidelines and standards for hydro-morphological streamflow monitoring;
11) Quantification of uncertainties;
12) Development of expert networks to advance methods.

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

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

The Surface Water and Ocean Topography (SWOT) satellite mission, launched in December 2022, marks a significant advancement in hydrological sciences. It is the first satellite designed to investigate surface water in the global water cycle, and it provides the first comprehensive view of Earth's freshwater bodies from space. Using Ka-band radar interferometry, SWOT delivers, for the first time, simultaneous, high-resolution measurements of water surface elevation and inundation extent in rivers, lakes, reservoirs, and wetlands globally. This dataset will fundamentally transform our ability to understand surface water and reveal new insights into hydrologic processes. The hydrologic remote sensing community has worked for more than a decade to develop new methods and scientific understanding that are now allowing SWOT data to advance knowledge of global water fluxes. For this session, we solicit abstracts presenting recent advances enabling SWOT to unlock new frontiers in hydrology and enhance our understanding of Earth’s surface water.

The moment when hydrology became recognised and established as a science remains a topic of debate. Certainly, there is a long tradition of theories on the natural occurrence, distribution, and circulation of water on, in, and over the surface of the Earth (Horton, 1931). While some of these theories remain valid today, others have been replaced by more recent understandings, which reflect the evolution of hydrology as a science.
As a scientific hydrological community, we are committed to advancing our field. Progress in hydrology can greatly benefit from a solid historical foundation, enabling us to assess past achievements, identify research gaps, and learn from earlier missteps. Accordingly, the newly formed IAHS Working Group on the History of Hydrology aims to foster a culture of historical hydrological literacy to support the growth of hydrological science by connecting it to its roots.
For this session, we welcome contributions that examine the evolution of hydrological concepts over time, how overlooked methods might hold contemporary value, and reflect on the factors that have led to incorrect conclusions, i.e. learn from mistakes. Topics of interest include the history of hydrological models and modelling, including deterministic vs stochastic approaches, optimisation, and diagnostic metrics; land-mark hydrological projects, the management of historical datasets or experimental catchments and their management, and the significant contributions of scientists, especially female hydrologists and other under-represented groups, as well as institutes and organisations. We encourage contributions from countries that are underrepresented in the historical hydrological literature.

Prof. Günter Blöschl will provide an invited talk on the 'Evolution in the Understanding of the Characteristics of Extreme Hydrological Events'.

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 building 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
- Impact on human well-being and health

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.

The approaches and methods we choose for a hydrological modelling study affect our modelling results and conclusions, and hence also their usefulness for decision support. As of today there is no common and consistently updated guidance on what good modelling practice is, and how we can achieve transparent, robust and reproducible workflows. While many useful practices such as scripted workflows, model benchmarking, controlled model comparisons, careful selection of calibration periods and methods, or testing the impact of subjective modelling decisions along the modelling chain exist, none of these can be considered common practice yet.

This session therefore 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 invite presentations of worked examples and software tools: What did(n’t) work? How were challenges overcome? How did developed workflows allow for detailed scrutiny of the techniques, assumptions, and interpretations of data, models, and their uncertainties? Contributions should aim to improve the scientific basis of (parts of) the modelling chain and put good modelling practice in focus again. This might include (but is not limited to) contributions on:

(1) Benchmarking to increase trust in model results
(2) Developing robust calibration and evaluation frameworks to improve transparency
(3) Going beyond common metrics in assessing model performance and realism
(4) Developing frameworks that enable hypothesis testing or consideration of alternative conceptual models
(5) Investigating subjectivity and documenting choices along the modelling chain
(6) Developing modelling protocols and/or scripted workflows to improve efficiency and reproducibility
(7) Examples of adopting the FAIR (Findable, Accessible, Interoperable and Reusable) principles in the modelling chain
(8) Methods for uncertainty analysis, data assimilation, and management optimization under uncertainty, e.g. in the decision-support context
(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

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.

Water in the snowpack 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 snowfall to rainfall, a modified total amount of precipitation, an earlier snowmelt, and a decrease in peak snow accumulation) will reflect on water resources availability for environment and anthropogenic uses at multiple scales. This may have implications for energy, drinking water and food production, as well as for environmentally targeted water management.

The generation of runoff in catchments that are impacted by snow or ice profoundly differs from rainfed catchments. Yet, our knowledge of snow/ice accumulation and melt and their impact on runoff is highly uncertain, because of both limited availability and inherently high spatial variability of hydrological and weather data.

Contributions addressing the following topics (but not limited to) are welcome:
- Experimental research on snowmelt & 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 addressing the impact of climate change and/or extreme events (e.g., droughts) on the water cycle of snow and ice affected catchments.
- Studies on cryosphere-influenced mountain hydrology and water balance of snow/ice-dominated mountain regions;
- Use of modelling to propose snowpack, snowmelt, icepack, ice melt or runoff time series reconstruction or reanalysis over long periods to fill data gaps;

This session will feature a solicited presentation by Prof. Bettina Schaefli from the University of Bern, Switzerland.

The session is linked to the IAHS HELPING working group on Droughts in Mountain Regions (https://iahs.info/Initiatives/Scientific-Decades/helping-working-groups/droughts-in-mountain-regions/)

Despite only representing about 25% of continental land, mountains are an essential part of the global ecosystem. They are also recognised as the source of much of the world's fresh water supply. A significant portion of the global population relies on their water supply, with around 26% living in mountain communities and 40% living in the downstream plains. Mountains are particularly sensitive to climate variability and change due to the heterogeneity of elevation-dependent hydro-meteorological conditions. This makes them unique areas for identifying and monitoring the effects of global change.

This session will bring together the scientific community developing hydrology research on mountain ranges across the globe to share results and experiences. We invite contributions addressing past, present and future changes in mountain hydrology due to changes in 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 to this session are:

- Sources of information for evaluating past and present conditions (in either surface and/or groundwater systems).
- Methods for differentiating climatic and anthropogenic drivers of hydrological change.
- Modelling approaches to assess hydrological change.
- Evolution, forecasting and impacts of extreme events.
- Case studies on adaptation to changing water resources availability.

Mountains receive and produce a high proportion of precipitation and runoff, forming the headwaters of many of the world’s major river systems and supplying water to at least half of humanity. These headwaters contain substantial snow and ice reserves and generally are undergoing amplified global warming resulting in rapid changes in landcover, permafrost, snowcover, glaciers, and hydrological regime. Because of the above, high mountain headwaters are the focus of global concern as exemplified by the UN International Year of Glaciers’ Preservation – 2025. Understanding and prediction of the mountain cryosphere and water cycle have been restricted by sparse observation networks, uncertainties in process representation and low model resolution, and substantial heterogeneity over small spatial scales. This session addresses the following questions: How can snow and ice hydrology best be measured in various alpine regions? How do land surface energy and water exchanges differ in various high mountain regions of the Earth? What improvements to high mountain hydrological predictability are possible in various alpine regions through improved process physics, representation of spatial variability, and incorporation of ground and remote observations? To what extent are existing model routines valid and transferrable amongst different alpine regions? Submissions that deal with observations and data, model application and diagnostic comparisons, new process understanding and insights, and better prediction of the changing mountain cryosphere and water cycle are welcome. This session is organized by and contributes to the International Network for Alpine Research Catchment Hydrology (INARCH; https://inarch.usask.ca/) of the World Climate Research Programme’s GEWEX Project.

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 across the region. Advances in hydrological models, including process- and machine learning- based 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 reduction still faces unsolved challenges.

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, seasonal to decadal forecasting, water resources management, climate change and impact assessments including compound and multi-hazard risks. We particularly welcome interdisciplinary studies that combine the physical drivers of water-related risks and their socio-economic impacts. Science for solution initiatives contributing to the IAHS HELPING decade are welcome.

Transboundary waters encompass aquifers, lakes, and river systems shared by two or more countries. These waters do not adhere to political boundaries, meaning that water use, pollution or overexploitation in one region can have significant consequences downstream. Effective transboundary water management is thus crucial to address pressing issues from water scarcity and biodiversity protection to economic growth and peacekeeping.
Over half of the global population resides in transboundary basins. Given the diverse physical, political, and socio-economic contexts of these shared water bodies, integrated approaches and practices are needed to solve transboundary water problems, to foster cooperation and to ensure sustainable management.

We welcome contributions demonstrating:
(1) Modeling and inter-comparison of different models (ranging from traditional hydrological models to innovative AI approaches and hybrid applications) for simulating water balance components and water quality including climate change impact studies, sensitivity analyses, uncertainty evaluations.
(2) Evaluation of performance and uncertainty of transboundary datasets of climate and hydrological characteristics, including remote sensing products and climate projections. We seek contributions that explore how remote sensing can help close the transboundary water data gap, offering cost-effective, solutions for monitoring and assessing water resources across borders.
(3) Applications supporting sustainable management of transboundary water including water abstractions, water-savings or water retention solutions in agriculture and industry.
(4) Development and implementation of Joint Monitoring and Information Systems, such as GIS-based databases, that facilitate effective cooperation in water-related risk reduction and transboundary resilience modeling. These include experiences with joint problem definition, creating a common understanding, and evaluating the effectiveness of implemented strategies.
(5) Involvement of Multi-Level Stakeholder engagement in shared water management. This includes capacity development, voluntary data collection through citizen science, participatory modeling, trust-building, and science-policy-driven decision-making.

The session is organized by the Danube Water Balance (DRP0200156 Danube Region Interreg Programme) and GRANDE-U “Groundwater Resilience Assessment through iNtegrated Data Exploration for Ukraine” (NSF Awards No. 2409395 and 2409396) teams.

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.

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.

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

Maintaining good water quality is essential for preserving the ecological, recreational, and industrial functions of our water resources. Water quality is mainly controlled by the catchment properties and hydro-meteorological conditions, with land use and climate change significantly altering the quantities and dynamics of particulate and solute concentrations at the outlet of catchments worldwide. This is especially true for agricultural catchments exposed to fertilization and increased erosion. However, catchments with other land use types are also prone to (negative) changes in water quality, for example, due to wastewater and road salt from urban areas or brownification in boreal forests. To address these diverse influences, water quality is typically monitored and assessed at the catchment scale. However, effective measures to prevent or reduce water quality deterioration are still hindered by our limited understanding of the underlying processes and causal relationships resulting from the complex interplay of hydrological, biogeochemical, and temporal factors.
Data-driven statistical analyses of discharge and concentration time series observed at catchment outlets (i.e., C-Q relationships) provide valuable insights into the underlying mechanisms, including process scaling and the effectiveness of measures.
The advantage of technologies and sensors for monitoring high spatiotemporal resolutions and the growing availability of long-term data can inform experimental and modeling studies, allowing us to progress from recognizing patterns to modeling and understanding processes. A profound understanding of solute and particulate mobilization, retention, and export mechanisms ultimately allows us to develop local or catchment-scale solutions to mitigate negative impacts on water quality and enhance sustainable land use management.

This session brings together contributions focused on analyzing or modelling solute and particulate export dynamics at the catchment scale with those focused on innovative monitoring techniques and the development of mitigation measures or other solutions to enhance or protect water quality.

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

Quantifying and understanding the impacts of global change (climate change and extremes, land use change and socio-economic developments) on clean water availability across space and time is critically important for ensuring that there is enough water of suitable quality to meet human and ecosystem needs at present day and in the future. Recent work has highlighted the importance of considering water quality as a key factor in limiting water supply for sectoral uses. Thus, there is an urgent need for tools such as models that span a gradient from purely statistical (e.g., machine learning) to process-based approaches, anticipating the combined impacts of climate and socio-economic changes on water quality and address the resulting environmental and societal consequences. Some of these tools, within both Bayesian and frequentist paradigms, enable consideration of prediction reliability, relating uncertainties to a decision makers’ attitudes and preferences towards risks, all while accounting for the uncertainty related to our system understanding, data and random processes. We seek contributions that apply modeling and other approaches to:
• investigate the combined impacts on water quality and quantity from climate change and/or extremes across local to global scales, including climate impact attribution studies;
• investigate the impacts of present and future socio-economic developments on surface and/or groundwater quality;
• quantify and couple supply and demand in support of water quality management including vulnerability assessment, scenario analysis, indicators, and the water footprint;
• project future water scarcity or water security (combining water quality & quantity) supply and demand in the context of a changing climate and other global change drivers;
• quantify the uncertainty of water quality model under drivers of global change;
• interpret and characterize uncertainties in machine-learning, AI and data-mining approaches that are trained on large, possibly high-resolution data sets;
• address the problem of temporal and spatial scaling (e.g. disparity of scales between processes, observations, model resolution and predictions) in water quality modelling;
• test transferability and generalizability of water quality findings;
• involve stakeholders in water quality model development to inform risk analysis and decision support;
• application of remote sensing in water quality estimates at multiple scales.

A large number of micropollutants, also known as trace contaminants or emerging contaminants, and their transformation products (veterinary and human pharmaceuticals, pesticides and biocides, personal care products, organic pollutants such as PFAS or chlorinated compounds) and heavy metals pose a risk for soil, groundwater and surface water. The large diversity of compounds and of their sources makes the quantification of their occurrence in the terrestrial and aquatic environment across space and time a challenging task. Regulatory monitoring 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. Notably, this session welcomes contributions focusing on circular economy principles, including case studies of emerging contaminants removal and recovery from water resources. The goal is to stimulate a dialogue that not only advances scientific knowledge but also promotes actionable outcomes that benefit society and the environment.
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 in the soil-groundwater-river continuum of catchments. The session additionally contributes to disseminating the REMEDI project results (Grant ID: 956384). REMEDI focuses on X-ray contrast medium agents and trains early-stage researchers to address pharmaceutical water contamination, treatment and recovery.

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.

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 and their interplay, develop robust methods for modelling and analyzing floods and droughts and their transitions, 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 or their interplay are of particular interest. We especially encourage submissions from early-career researchers.

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 rivers and catchments, such as the construction of reservoirs, alterations 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 also welcome. 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 the 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, reservoir construction, 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.

Assessing the impact of climate variability and change on hydrological systems and water resources is important for society to better adapt to future shifts in water availability and extreme events such as floods and droughts. However, significant uncertainties remain in projecting these impacts, particularly those associated with internal/natural climate variability and hydrological response to changes in climatic forcing at multi-annual to multi-decadal timescales. Differences in model realizations, interannual to decadal variability, and the influence of major climate modes (e.g., ENSO, NAO, AMO) can substantially modify hydrological responses, potentially altering the expected effects of human-induced climate change. Understanding how these climate patterns interact with catchment properties (e.g., vegetation cover and groundwater support) and land-use changes is essential for improving hydrological predictions.

Catchments are complex systems that respond to climate forcing across multiple timescales. Yet, hydrological models often struggle to accurately capture these responses, suggesting potential misrepresentation or omission of key processes, timescales, and feedback. It is necessary to disentangle the interactions between hydrological, biophysical, and climatic drivers to enhance model realism and predictive skills.

This session invites contributions that advance our understanding of hydrological variability and extremes under climate variability and change, including:
1. The role of internal climate variability in shaping hydrological extremes and long-term water resource availability;
2. Advances in understanding hydrological and biophysical processes governing catchment responses to climate shifts;
3. Studies applying hydrological regularities (e.g., the Budyko hypothesis) to improve predictions under changing conditions;
4. Investigations of catchment “memory” and its representation in models;
5. Efforts to enhance the robustness of hydrological simulations under future climate variability and change through newly developed probabilistic and storyline impact scenarios.

The relationship between land cover, land use, and water resources is complex and bidirectional. Changes in land cover and use can dramatically alter water circulation, availability, quantity and quality, while water resources significantly shape land cover patterns and ecosystem health. Land cover changes are determined by many environmental factors, including water circulation, landscape quality, and ecosystems. Climate variability and land cover changes have been shown to alter the quality and availability of freshwater resources around the world at multiple scales. Human activity is the main driving force influencing land cover changes. Globally, land cover change is a dominant factor affecting ecosystems and the hydrological regime. Land use and land cover changes (LUCC) directly affect the magnitude of evapotranspiration, surface runoff, groundwater recharge by infiltration, and even precipitation. Generally, evapotranspiration, surface water storage, and groundwater recharge are interrelated processes that regulate the balance in the water dynamics of the entire basin. From the point of view of water management, the simulation of land use changes is very important because it provides future scenarios and patterns for water resources.
The main objective of the session is to discuss the role of land use/land cover changes in different regions and diverse scales in accelerating hydrological processes and altering water resources. The main topics should include the following problems:
1. Transitions of LULC changes in different landscapes,
2. Impact of LULC changes on ecosystems and the risk of floods and droughts,
3. Indicators of water resources including LULC changes,
4. Modelling of hydrological processes including LULC changes,
5. Projections of water resource changes affected by LULC and climate change,
6. New data sources to detect LULC changes

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.
Improving our understanding of how forest-water interactions are shaped by physiographic, biogeochemical and hydrometeorological factors and how forested catchments respond to dynamic environmental conditions and disturbances, is critical for protecting and managing our forest ecosystems. Building this knowledge requires interdisciplinary approaches in combination with new monitoring methods and modeling efforts.
This session brings together studies that aim to improve our understanding of water-forest dynamics and stimulate discussion 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.

Solicited talk by Noemi Vergopolan (Rice University): "Improving Forest Realism in Earth System Models through Satellite Observations"