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.

Since the 1980s, various approaches have been developed to address contaminated sites and old landfills, ranging from excavation to advanced in-situ treatment technologies. There is a need post evaluate such sites. While significant progress has been made, ongoing challenges such as the long-term sustainability of these methods and impacts of climate change call for a rethinking of strategies. Emerging contaminants like PFAS (per- and polyfluoroalkyl substances) and microplastics have recently gained attention due to their persistence in the environment and toxicity. New techniques are needed to monitor and treat these. Urban infrastructure projects commonly encounter contaminated soils. For such situations soil washing is becoming an increasingly common ex situ technology to remove contaminants from the soil with a combination of physical separation and chemical leaching by aqueous solutions, creating valuable materials such as gravel and sand. This also reduces the need for waste deposits. Supported by appropriate regulations and sustainability assessment tools, we can push towards a more circular mass handling.

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

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

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

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

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

High-resolution hydrometric monitoring of rivers is important because climate change severely affects frequency and magnitude of extreme events and flood/drought risk profiles are changing fast. However, hydrometric monitoring data is scarce and lacks spatial resolution and coverage, particularly in remote and hard-to-reach rivers in alpine, Arctic and tropical regions. Advanced in-situ monitoring technologies have to be combined with satellite earth observation (EO) to obtain accurate, reliable, long-time and spatio-temporally resolved information for effective decision support, risk assessment, investment analysis in the context of climate change adaptation, and operational forecasting, surveillance, and management.

Traditional in-situ hydrometric monitoring of rivers is station-based. Water surface elevation, flow velocity, bed geometry and river discharge are measured using sensors that are installed in-situ, either in direct contact or in close proximity to the flow. In-situ station-based monitoring infrastructure is vulnerable and often fails during extreme flooding events, when the value of information is very high. Station-based monitoring networks lack spatial resolution and have been declining in many regions, particularly in remote and hard-to-reach areas. Data accessibility is increasingly restricted because of growing conflicts between countries over water resources allocation.

This session solicits contributions describing new water observing systems providing key hydrometric variables (e.g. bathymetry, velocity, discharge, water surface elevation, temperature, water quality parameters) at high spatial resolution and coverage, using ground-based, satellite, and/or unoccupied arial system (UAS) platforms. Focus is on the development of innovative monitoring technologies, the combination of in-situ, airborne, and satellite EO datasets, and data use for river modeling and decision support.

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.

The Critical Zone (CZ), encompassing the Earth's outer layer from the top of the vegetation canopy to the bottom of the circulating groundwater, is essential for sustaining life and maintaining environmental health. Understanding this complex zone requires a collaborative, multidisciplinary approach that transcends disciplinary and national boundaries, bridging gaps between short-term and long-term environmental processes. This session will highlight CZ science, CZ methodologies, and the collaborative efforts of CZ networks from around the world. Topics of interest include, but are not limited to: Innovative techniques in CZ research and monitoring, including contributions involving observations, modeling, or integration of the two; Advances in understanding soils, hydrology, and biogeochemical cycling within the CZ; Characterization of CZ structure as it varies with depth and environmental factors; Impacts of stressors and environmental change on the CZ; Policy or management implications of CZ research; Development of CZ science networks; and Case studies of successful international CZ collaborations.

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.

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. KlemeŠ (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

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.

Continuous changes in global climate are increasing the intensity, frequency, and duration of climate extremes with deep implications for achieving sustainable and just societal development. Given its extensive global coverage and profound interactions with freshwater resources, agriculture is one of the human activities most exposed to climate extremes. Food systems can be directly impacted by extreme climate events (e.g., droughts, floods, and heatwaves). At the same time, climate extremes can exercise substantial influence on water resource availability (e.g., declines in water availability, water pollution) with cascading implications for the productivity and stability of food systems. These consequences are made more complex by growing reliance on food trade and strong water-food-energy interconnections. To fully understand the rising role of climate extremes within water-food systems, new research is needed that provides quantitative approaches to measure the impacts of climate extremes and identifies and tests feasible solutions to mitigate impacts.
In this session, we call for contributions investigating all aspects of interactions between climate extremes and water-food systems, including determining the extent and magnitude of climate extreme impacts on water-food systems, understanding the mechanisms driving the changes of water-food systems under climate extremes, and proposing nature-based or human intervention solutions to mitigate these climate extreme challenges.

Increasing magnitude, duration and frequency of extreme temperatures (high and low) that can impact the quality and quantity of water resources necessitate a clear understanding of their interactions. This session aims to address the multifaceted causes and consequences of temperature extremes on water resources (both quality and quantity). We seek to understand, model and predict water resources’ responses to temperature-induced hazards (e.g., heatwave, cold spell, drought and wildfire) in current and future climates. We welcome novel methodologies, including experimental studies, field measurements, remote sensing and modeling under various temperature-water use scenarios considering physical, environmental, social and economic aspects.
This session invites submissions on (but not limited to): (I) Novel research on impacts of temperature extremes such as heat waves, cold waves, droughts and wildfires or their combination as compound events on water quantity and quality; (II) Proper frameworks, including modeling (physical, statistical/stochastic, data-driven models particularly machine learning), instrumentation, datasets (field, remote sensing), indicators and measures, to predict and manage causes and effects of temperature-induced hazards on water resources; (III) Innovative methods for vulnerability, resilience and impact assessment of temperature-related water resources hazards; (IV) Risk assessment frameworks for managing impacts of temperature extremes (due to climate change and anthropogenic forcing e.g., LULC changes, urbanization, improper management) on water resources; (V) Uncertainty analysis in the context of temperature-induced hazards, offering insights into how uncertainty can be quantified, managed and communicated; (VI) Case studies with different physical features, particularly water-stressed regions to analyze water scarcity and related challenges for areas that are most vulnerable to temperature-induced hazards; (VII) Assessment and development of water policy and water management plans to adapt to changes and mitigate impacts.
By bringing together experts from various fields, the session will contribute to a deeper understanding of the complex interactions between temperature extremes and water resources, ultimately informing decision support systems and sustainable management plans. We encourage students, scientists, researchers, stakeholders and policymakers to submit their abstracts and join us in exploring this vital challenge.

This session welcomes cross-cutting advances in theoretical, methodological and applied studies at the synergistic interface among physical, analytical, information-theoretic, kinematic-geometric, machine learning, artificial and systems intelligence approaches to complex 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, artificial and systems intelligence with process understanding in mind.

The session further encompasses practical aspects of working with systems intelligence and emerging technological approaches for strengthening systems analytics, causal discovery, model design and evaluation, predictability and uncertainty analysis, along with geophysical automated learning, model design, prediction and decision support.

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.

Water stored 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 potential 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. 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 high spatial variability of hydrological and weather data in such areas.

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.

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.

Water resources are a strategic issue in drylands globally as these environments are by definition water-limited, making them highly sensitive to changes in regional water balances and vulnerable to extreme events such as droughts and floods. Drylands face challenges from changing hydrological conditions and landscapes, driven by climatic and anthropogenic factors, affecting freshwater availability and quality. However, many aspects of the functioning of these systems are poorly understood or often treated in a disciplinary manner. Yet, interdisciplinary research is essential to improve the understanding of hydroclimatic processes in these regions and the human impacts on water resources, to achieve sustainable development goals. We welcome submissions focusing on processes in dryland research across a broad geographical range, from Mediterranean drylands to hyperarid deserts, to build an interdisciplinary session including topics such as:
Estimation of the spatiotemporal variability of water fluxes: rainfall, soil moisture, evapotranspiration, floods and droughts
Hydro-geomorphological impacts of extreme events
Transport and deposition of river sediments and their impact on channel morphology
Groundwater recharge process estimation
Quantification of the impacts of anthropogenic water abstraction?
Climate dynamics and their influence on dryland water balance including paleo-reconstructions and projected future scenarios
Transmission losses and intermittent stream functioning

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 in monitoring flow intermittence, both in-situ and with remote sensing,
· novel approaches and applications in modelling non-perennial reaches, networks and catchments,
· 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.

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.

The Danube River Basin (DRB) is one of the most diverse transboundary river system in the world in terms of the number of countries that share over its territory with different natural, cultural, societal and economic backgrounds. The assessment of quantity and quality of water resources and their changes in such a diverse system requires transnational and interdisciplinary approaches and cooperation.
We welcome contributions demonstrating:
(1) Modeling and inter-comparison of different models 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.
(3) Applications supporting sustainable management of transboundary water including water abstractions, water-savings or water retention solutions in agriculture and industry.

Transboundary waters encompass aquifers, lakes, and river basins shared by two or more countries. These waters do not adhere to political boundaries, meaning that pollution or overexploitation in one region can have far-reaching consequences beyond borders. Effective transboundary water management is 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. With 286 transboundary river and lake basins covering nearly half of the Earth’s surface, and 592 identified transboundary aquifers, the need for cooperative management is urgent. Given the diverse physical, political, and socio-economic contexts of these shared water bodies, no single approach can solve transboundary water issues. Instead, a suite of practices is required to foster cooperation and ensure sustainable management.
We invite submissions with a focus on (but not limited):
1. Approaches to Assessing Water Quantity and Quality: methods ranging from traditional hydrological models to innovative AI approaches and hybrid applications. We encourage case studies that demonstrate successful application in various transboundary contexts.
2. Remote Sensing Technology Applications: We seek contributions that explore how remote sensing can help close the transboundary water data gap, offering cost-effective, scalable solutions for monitoring and assessing water resources across borders.
3. Development of Joint Monitoring and Information Systems: submissions creating and implementing joint monitoring systems, such as GIS-based databases, that facilitate effective cooperation in water-related risk reduction and transboundary resilience modeling.
4. Water Resources Management Strategies: development and follow-up of water management strategies in transboundary basins. This includes experiences with joint problem definition, creating a common understanding, and evaluating the effectiveness of implemented strategies.
5. Multi-Level Stakeholder Involvement: experiences highlighting 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 GRANDE-U team “Groundwater Resilience Assessment through iNtegrated Data Exploration for Ukraine” (NSF Awards No. 2409395 and 2409396).

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.

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, while also considering the compositional nature of geochemical data. 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 biogeochemistry. We are expecting novel approaches that allow merging hydrological modelling with studies of biogeochemical 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. This 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 catchment outlet. To address these 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 analysis of discharge and concentration time series observed at catchment outlets provides valuable insights into the underlying mechanisms, including process scaling and the effectiveness of measures. The growing availability of data from long-term, high-temporal and high-spatial resolution monitoring of water quality can inform experimental and modeling studies, allowing us to progress from recognizing patterns to the understanding and also modeling of processes. A profound understanding of solute and particulate mobilization, retention, and export mechanisms ultimately allow us to develop local or catchment-scale solutions to mitigate negative impacts on water quality.
This session brings together contributions focused on analyzing or modeling solute and particulate export dynamics at the catchment scale with those focused on the development of mitigation measures or other solutions to enhance or protect water quality.
Examples include solute or particulate export patterns and C-Q relationships under variable hydro-meteorological conditions or contrasting landscapes, mitigation measures based on best practices as well as innovative measures under development or tested under lab-scale conditions.

Agricultural activity has a significant impact on the environment, starting with the clearing of natural land for cultivation. This process disrupts the hydrological cycle and increases the risk of laminar erosion in rills and gullies. Erosion also occurs during tillage and harvesting, while agrochemicals contaminate soils, as well as surface and groundwater. Additionally, a large portion of available water resources is consumed for irrigation.

Addressing these challenges is crucial for the future of humanity. A comprehensive approach requires a productive balance between direct data and observations, along with modeling tools, as data is essential for accurate model evaluation.

This session aims to explore several key areas, at the agricultural watershed scale: the characterization of hydrological, erosive, and agrochemical export behavior in agricultural watersheds worldwide; problem diagnosis; new technologies and sensors for monitoring these variables; innovative watershed modeling techniques to evaluate the impact of agriculture on water quality and soil erosion; and the identification of scenarios, through modeling, that minimize the adverse effects of agricultural practices. The ultimate goal is to foster more sustainable and environmentally responsible agriculture.
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Agriculture impacts the environment by disrupting the hydrological cycle, causing erosion, and polluting water with agrochemicals. This session covers key areas like watershed monitoring, innovative modeling techniques, and solutions to minimize negative effects, aiming for sustainable agriculture.

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