The Danube River Basin, spanning 19 countries and covering 801,000 km², is the most international river basin in the world. This region faces diverse challenges related to water quantity, quality, groundwater management, and biodiversity, all of which are expected to intensify due to climate change. To address these challenges, a holistic and sustainable water management approach is needed—one that integrates environmental, social, and economic dimensions, ensures stakeholder involvement, and aligns with regulatory frameworks.

Building on the Planetary Boundaries framework, the concept of Safe Operating Space (SOS) has emerged in the last decades to assess sustainable resource use within the Earth’s carrying capacity while maintaining human well-being. Within the Horizon Europe SOS-Water project, we are working to define the SOS for water resources in four case study sites across Europe and beyond (Danube, Rhine, Jucar and Mekong basins) using integrated modeling, monitoring, advanced indicators, and an inclusive and iterative participatory approach that actively engages stakeholders to co-define visions, water values, and management options.

The resulting co-created SOS framework will inform the design of sustainable water management pathways that address current and future challenges. It aims to maximize the socio-economic and ecological value of water while promoting resilience and sustainability across the different river basins.

This proposed talk will showcase the application of the SOS framework to the Danube Basin, highlighting its capability to integrate all the different aspects of the water dimension with stakeholder engagement and co-development of management pathways. We will present the preliminary framework co-developed with stakeholders for the Danube Basin and provide insights into the how it can be used to inform sustainable water management practices and address the critical water challenges facing the Danube Basin and other transboundary regions worldwide.

How to cite: Artuso, S., Politti, E., Tramberend, S., Smilovic, M., and Kahil, T.: Developing a Safe Operating Space framework for water resources in the Danube River basin, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5915, https://doi.org/10.5194/egusphere-egu25-5915, 2025.

Beside common pollutants, such as organic material and nutrients, an ever-widening list of chemicals also put pressure on the quality of our rivers, lakes and the health of the prestigious ecosystems living within them. An investigative work to understand the main sources and pollution pathways of these chemicals is an important task ahead of us. A series of large-scale studies have been undertaken with the cooperation of experts from almost all Danube countries to build a hazardous substance inventory in the first step and then to build an emission model based on this inventory. The inventory has been built within the frames of the Danube Hazard mᶾc InterReg project, the model building is currently ongoing within the frames of the Tethys InterReg project. Three chemical groups are investigated by applying the MoRE (“modelling of Regional Emissions”) model for the Danube River Basin (DRB) represented by key elements and compounds: the group of potentially toxic elements is represented by 6 heavy metals and arsenic, industrial chemicals are represented by the two most common per- and polyfluoroalkyl substances (PFAS), PFOS and PFOA, and human pharmaceuticals are represented by a pain killer (diclofenac) and a psychoactive drug (carbamazepine). Each of these substances are ubiquitous in the environment but linked to different sources and pathways. While the source of pharmaceuticals is fairly well known, the estimation method for their emissions is challenging if one needs to reflect regional differences of it or to account for the effects of the type of sewage treatments applied in the treatment plants. Heavy metals are abundant in soils all over the DRB, while the uncertainties of the emissions from operating and abandoned mining facilities are also key to be addressed if hot spots to be identified. The most difficult, however, is the regionalisation of PFAS substances as beside emissions from point sources and urban runoff, they appear in atmospheric deposition all over the basin and in groundwater around known and potential hot-spots, meanwhile the actual emissions from point sources are also much less documented. A key step to upgrade our inventories for the model is that the emission from industrial facilities to air and water are described in detail as far as data from national and international databases, literature or BAT documents is available. Knowledge gap is indicated by the amount of plants with known discharge (162) compared to all the industrial facility in the DRB (6258 facility identified in the Industrial Emission Directive database). For the most uncertain emission sources and pathways, the study aims an order of magnitude estimation for all the potential estimation sources. Hence, for example tile drain pathway has been introduced for chemicals present in soils, despite the lack of sufficient concentration data in effluents. The estimation of groundwater concentration is not only difficult for diffuse sources but also for hot spots, which may be known only by literature information. The latter (literature values) is applied for landfill sites, which are treated as legacy hot spots for PFAS substances and pharmaceuticals.

How to cite: Jolánkai, Z., Kardos, M. K., Dudas, K., Potó, V., and Clement, A.: Building a transboundary hazardous substance emission model for the Danube River Basin. Overview of the key challenges of data availability, data uncertainty, knowledge gaps of substance behaviour, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20798, https://doi.org/10.5194/egusphere-egu25-20798, 2025.

Chemicals are part of our life. Several hundred thousand are used in multiple applications in the European Union (EU) and may ultimately reach water systems. Chemicals are used as pharmaceuticals, personal care products, pesticides/biocides or so-called industrial chemicals. Losses to the environment may occur throughout all stages of the life-cycle of products. Specifically, mobile, persistent and toxic chemicals (PMTs) are considered as major concern for human and environmental health. Exceedances of current environmental quality standards (EQS) are recorded all over Europe. A significant increase in the number of chemicals that need to be considered and a major tightening of EQS is currently under discussion in the EU.

Emission, fate and transport models can help to map the temporal and spatial variability of environmental exposure and support risk assessment for water bodies where monitoring is lacking. They can be used to identify sources and pathways responsible for current exposures and to assess the impact of potential future developments of PMT-exposures in surface water and groundwater. Such scenario assessment may include changes in PMT use, effects of pollution control measures, accidental spills and climate change impacts. TU Wien led and still leads various research projects for the enhancement of monitoring, modelling and management of PMTs in the Danube Basin: (i) Danube Hazard m³c (EU Interreg Danube Transnational Program) (ii) the “Danube case study” in the frame of the project PROMISCES (EU Horizon 2020) and (iii) Tethys (EU Interreg Danube Region).

This contribution provides a short overview on basic considerations, concepts and methods of these activities and exemplifies them on the case of water pollution with per- and polyfluoroalkyl substances (PFAS) in the upper Danube Basin. Investigations show that an upstream located chemical park and diffuse inputs from urban areas are the main sources of perfluorinated carboxylic acids (PFCA) for surface waters. For perfluorinated sulfonic acids (PFSA), diffuse urban inputs predominate. A large part of the overall emissions is due to legacy pollution, which will persist even if strict source control for PFAS is implemented. Wastewater treatment effluents contribute a share of up to 25% of emissions for both PFAS groups.

Most of the surface waters in the upper Danube River Basin, including the Danube itself, show a low risk of exceeding the threshold of the EU drinking water directive of 100 ng/l for the sum of 20 PFAS. This is of relevance in case that surface waters are used as drinking water source via bank filtration. There is nevertheless a high risk of exceeding the European Commission’s proposed quality standard for surface and groundwater of 4.4 ng l-1 PFOA toxicity equivalents as a sum of 24 PFAS in the Danube and in most of its tributaries. Simulated scenarios show that these risks may be reduced by massive efforts to implement water pollution control measures (including groundwater remediation in hot spot areas). However, the risk might even increase if low effort is made to control water pollution and at the same time the Danube’s flow decreases due to climate change.

How to cite: Zessner, M., Liu, M., Kittlaus, S., and Zoboli, O.: Monitoring, modelling and management of persistent, mobile and toxic chemicals in the Danube River Basin, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5883, https://doi.org/10.5194/egusphere-egu25-5883, 2025.

The Danube Water Balance project launched in 2024 in the frame of the Interreg Danube Region Programme with the aim to i) develop a harmonized hydrological modeling system enabling the analysis of present and future water balance of the Danube basin and to ii) improve data management among Danube countries for present and future water balance calculations. The latter is partially based on the establishment of a data repository for input data of the model. Besides global and regional open access data (e.g. digital elevation model, climate variables), national data are collected in order to i) provide direct input for the model, ii) validate global/regional data and iii) allow for the calibration and validation of the model. Thematically, the data cover environmental, hydrologic and water management, and socioeconomic information. Here, we present the procedure and the results of the collection of national data, starting from the identification of data types, desired quality and relevant resolution through the statistics of collected data to the outcomes of a preliminary data gap assessment. Spatial and temporal data coverage patterns by countries/regions are evaluated, taking into account the differences in environmental conditions and water management specificities. We also present the future steps planned in the project towards a harmonized basin-wide database.

This work/paper was supported as part of DANUBE WATER BALANCE, an Interreg Danube Region Programme project co-funded by the European Union.

How to cite: Kozma, Z. and the Danube Water Balance project data collection team: Establishment of a data repository for hydrological and related data to support water balance modeling in the Danube basin, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17084, https://doi.org/10.5194/egusphere-egu25-17084, 2025.

Understanding groundwater dynamics is crucial for assessing groundwater resilience and supporting water management, particularly in transboundary areas where shared aquifers are often evaluated only at a national level, overlooking the broader aquifer system and data from neighboring countries. Groundwater resilience—the ability of groundwater systems to recover from disturbances such as droughts—is a spatially variable trait influenced by a range of spatial-temporal factors that do not obey borders. This study investigates the spatial and hydrodynamic controls on groundwater dynamics within the Baltic region, focusing on the challenges posed by data discrepancies and monitoring network inconsistencies across Latvia, Lithuania, and Estonia. 

We utilized groundwater timeseries indices and the groundwater memory effect to investigate dominant patterns and their correlations with physiographic and climatic controls. Machine learning algorithms were used to explore spatial patterns with similar hydrodynamic characteristics. The analysis of national groundwater level data revealed monitoring gaps, particularly in transboundary aquifers, along with different national approaches in groundwater monitoring networks. These challenges complicate the comprehensive assessment of groundwater dynamics at a regional scale.

The results reveal that topographic, climatic and hydrological features are the most significant drivers of groundwater dynamics, followed by geological features. Groundwater indices and trends highlighted not only natural variability but also anthropogenic impacts on aquifer systems near large cities (e.g. Riga) and mining sites (e.g. Kohtla-Järve). We identify regions lacking monitoring wells and propose potential locations for new groundwater wells based on physiographic and hydrodynamic characteristics. 

This research is supported by the GRANDE-U “Groundwater Resilience Assessment through Integrated Data Exploration for Ukraine” (No. 2409395) project. 

How to cite: Bikše, J., Haaf, E., and Retike, I.: Groundwater dynamics across borders: data and monitoring network challenges in the Baltic countries, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16367, https://doi.org/10.5194/egusphere-egu25-16367, 2025.

Groundwater is a critical resource that supports ecosystems, agriculture, and drinking water supply, yet its sustainable management faces challenges, particularly in the transboundary regions. Collaborative approaches are needed to protect this shared resource, as pollution or overexploitation in one country can have significant consequences across borders. The Estonian-Latvian transboundary area is a good example of these challenges, with its reliance on both unconfined Quaternary aquifers, essential for ecosystems and rural communities, and confined first bedrock aquifers, critical for centralized water systems.

This study develops a transboundary aquifer vulnerability assessment framework, integrating harmonized methodologies to evaluate natural vulnerability and pollution risk. The analysis uses the DRASTIC and modified DRASTIC index-based methods, combined with the DRASTIC-L approach, which incorporates land use data for a comprehensive evaluation of both natural and anthropogenic pressures. To improve the reliability of the assessment, pollutant travel time calculations were used to validate the findings.

The results show high variability in aquifer vulnerability across the study area. The unconfined Quaternary aquifer is most vulnerable in regions with sandy sediments, shallow groundwater tables, and high recharge rates. The confined bedrock aquifers are covered with protective sediment layers, but their vulnerability varies depending on sediment thickness and hydraulic conductivity. Notably, discrepancies between Estonian and Latvian geological data were uncovered, as large polygons of well-protected areas often terminate abruptly at the border, highlighting inconsistencies in geological data between Estonia and Latvia.

This framework emphasizes the importance of integrating natural vulnerability maps, pollution risk assessments, and harmonized methodologies developed for regional geological conditions. The study offers a scalable and adaptable solution for transboundary aquifer management by addressing data inconsistencies and fostering international cooperation.

Integrating these insights into transboundary water management strategies can greatly improve decision-making by providing a more comprehensive understanding of groundwater vulnerability and pollution risks. Additionally, it helps to make groundwater systems more resilient to future challenges like climate change, land use changes, and increasing water demand. Ultimately, this approach supports the sustainable use and protection of shared groundwater resources, ensuring their availability and quality for current and future generations.

How to cite: Männik, M., Bikše, J., and Karro, E.: Advancing harmonized groundwater vulnerability assessments for sustainable management in the Estonian-Latvian transboundary aquifers, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10445, https://doi.org/10.5194/egusphere-egu25-10445, 2025.

The study assesses dynamics of transboundary water cooperation in the Mekong River Basin focusing on relationships between China and the Lower Mekong countries, namely, Myanmar, Thailand, Laos, Cambodia, and Vietnam. Water diplomacy is deployed as an analytical framework to investigate the extent to which China's Lancang Mekong Cooperation (LMC) since 2015 has carved out a new geopolitical, economic, and environmental landscape. The LMC has become influential and competes with other cooperation mechanisms, such as the Mekong River Commission. China has shared more hydrological data and information and releases emergency water downstream for addressing droughts. These do not demonstrate China's shift toward cooperation but could be regarded as China's 'dressing up domination as cooperation'. 

How to cite: Lee, S. and Shin, N.: The Emergnece of the Lancang Mekong Cooperation and its Impacts on the Mekong River Basin, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-96, https://doi.org/10.5194/egusphere-egu25-96, 2025.

Despite the progress in Polish-Ukrainian cooperation on transboundary waters through the establishment of joint regulatory bodies and legislative agreements, the problem of integrated groundwater monitoring still remains unresolved. This study presents the application of remote sensing to address data gaps concerning transboundary groundwater resources. The main advantage of remote sensing measurements is that the data they provide are temporally consistent and include spatial information, unlike point-based in-situ observations. Moreover, due to the use of multiple sensors, remote sensing enables comprehensive studies over large areas simultaneously, which is typically challenging in inaccessible regions.

Currently, only the GRACE/GRACE-FO mission (Gravity Recovery and Climate Experiment and GRACE Follow-On) provides direct measurements of terrestrial water storage (TWS) changes, which are largely governed by groundwater storage capacity. Our study presents the quantification of groundwater resources in terms of fluctuations in the shallow unconfined water table by integrating GRACE/GRACE-FO gravity data, precipitation observations, evapotranspiration, river runoff, and groundwater depth. Using machine learning algorithms, data from multiple sources were assimilated, achieving accurate groundwater quantification at a spatial resolution of 0.1°. Previous assessments of transboundary groundwater resources in the Bug River basin were based on a sparse and uneven observational network with a density of 0.003 points/km², as well as old (often from the 1980s) hydrogeological maps at a scale of 1:50,000.

The results of our novel approach indicate that groundwater resources in the study area are depleting, primarily due to increased evapotranspiration, despite a stable precipitation level of around 700 mm/year. According to GRACE/GRACE-FO observations, between 2012 and 2023, TWS in the Bug River basin decreased at a rate of 8.8±5.2 mm/year. Our comprehensive study serves as a source for the reassessment of available groundwater resources, providing information on the sustainable allocation of transboundary groundwater resources between Poland, Ukraine, and Belarus.

The study was conducted as part of the project GRANDE-U “Groundwater Resilience Assessment through iNtegrated Data Exploration for Ukraine” (NSF Awards No. 2409395 and 2409396).

How to cite: Solovey, T.: Remote sensing’s role in improving transboundary groundwater monitoring  and sustainable management: The Bug Basin, Polish-Ukrainian-Belarusian Borderland, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1338, https://doi.org/10.5194/egusphere-egu25-1338, 2025.

The St. Mary and Milk River (SMM) basin is an international transboundary watershed flowing between Canada and the United States. The basin is composed of 2 distinct headwater basins that flow into the Saskatchewan Nelson and Mississippi basin, respectively. A diversion constructed in 1909 conveys water from the higher-yielding St. Mary River into the lower-yielding Milk River. The 1909 Boundary Waters Treaty between the USA and Canada allowed for specific entitlements for each country, allowing for sharing of the combined basin resource between both countries. Lack of storage, conveyance and changing hydrological conditions in the basin have resulted in both countries receiving less than the treaty entitlement, prompting the International Joint Commission (IJC) to study the situation. This research addresses an important part of the IJC study which required implementing hydrological models to simulate natural flow in the SMM basin and understand the reliability of any solution under future climate. The HYPE hydrological model with the HDS module was implemented to model natural flow in the basin. HDS allowed for the explicit representation of the contributing area dynamics of prairie potholes which significantly impact the hydrology of the Milk River. The model was then used to run an ensemble of statistically downscaled future climate scenarios based on the CMIP6 models. Explicitly representing prairie potholes under future climate provided an opportunity to examine how non-contributing area might change in the future. We present an evaluation of historical model performance, a future climate analysis of streamflow in the basin, and the implications of the future climate conditions on apportionment practices in the basin. Results from this research will inform IJC decisions on future practices and infrastructure in this important transboundary basin and may add a new dimension to future practices as the effects of prairie potholes have never been explicitly considered.

How to cite: Coderre, P., Ahmed, M. I., Keshavarz, K., and Pietroniro, A.: Implementation of a hysteretic depression model to assess future water availability in the St. Mary and Milk River transboundary basin, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12597, https://doi.org/10.5194/egusphere-egu25-12597, 2025.

The Upper Danube Basin upstream of Vienna, which can be regarded as the water tower of the Danube region, has a long history of human influence on river flow, from land use changes to hydropower development and today’s anthropogenic climate change. At the same time, the civilizing activities in the basin also have included the collection of scientific data, leading to remarkably long and reliable observational hydro-meteorological time series by Swiss, German and Austrian hydro-meteorological services and authorities.

Based on these observational data sets, this contribution presents exceptionally long hydrological simulations for the Upper Danube Basin, spanning from the time of the industrial revolution (1870) to the record-breaking hot years of the last decade (until 2023). An existing, well-established model for the Danube basin (Kling et al., 2012, Stanzel and Kling, 2018) was re-applied, but with new input data sets and new parameterization. This long simulation time-series (1870-2023) allows a rigorous testing of the hydrological model’s capabilities to adequately simulate non-stationary conditions, by evaluating different periods with specific characteristics and the representation of slow changes and long-term trends. The simulations facilitate the analysis of complex changes in the water balance and the impact on river discharge, both in the past and in the future.

In the framework of the climate change impact research project STREAM (Storylines of Danube Streamflow), the hydrological model of the Upper Danube will be applied to simulate future Danube discharge conditions based on the latest CMIP6 climate model projections.

References:

Kling H, Fuchs M, Paulin M. 2012. Runoff conditions in the upper Danube basin under an ensemble of climate change scenarios. Journal of Hydrology Vol. 424-425, p. 264-277

Stanzel P, Kling H. 2018. From ENSEMBLES to CORDEX: Evolving climate change projections for Upper Danube River flow. Journal of Hydrology Vol. 563, p. 987-999

How to cite: Kling, H., Stanzel, P., Lerche, F., and Ossó, A.: Hydrological simulation of Danube River discharge over the last 150 years and future projections with CMIP6 until 2100, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18525, https://doi.org/10.5194/egusphere-egu25-18525, 2025.

Riparian strips form a transition zone between terrestrial and freshwater ecosystems providing essential ecosystem services. Healthy strips are crucial for the stability and sustainability of ecological systems. Riparian zones have major environmental importance because these could be interpreted as collision zones of transporting pollutants (on both surface and subsurface) from the land to the freshwater. According to that riparian zones have irreplaceable effect on sediment- and nutrient mitigation and securing freshwater ecosystem biodiversity.

Despite their vital importance, the research community paid less attention on riparian strips. Policy-level regulation of land use and related pollutant emissions within strips is also lacks. As a result, degradation of riparian habitats is still increasing.

In this study, we determined of a critical delineation distance of riparian strip with the fixed buffer strip approach. This was based on the analyses of almost 5000 computed local groundwater – surface water gradients in four counties of the Danube River Basin. We evaluated the actual and historic land use conditions within the derived riparian strips. To establish and understand the motivations and cause-effect relationship behind the land use arrangement, we examined the vegetation biomass production inside and outside the defined zone. In addition, to gain a more accurate understanding of the water balance processes of the riparian strips, we performed three types of trend analysis on the groundwater well time series.

Based on our results, the distance from the watercourse influenced the historical trends of groundwater wells. We highlighted in our results, that the proportion of agricultural areas exceeds national level ratios concerning natural land cover types within the riparian strips. For most countries of the Danube River Basin, the agricultural land use category shows up to almost 10% increase within the riparian strips compared to outer zones regarding a crop yield indicator. This means, that within the riparian strips, areas with significant potential for provisioning services are primarily exploited, to the detriment of regulating services. This revealed conflict is also an opportunity that affects the feasibility of several European Union strategies (Water Framework Directive, Biodiversity Strategy until 2030), by pointing out potential restoration sites.

How to cite: Decsi, B., Koncsos, L., and Kozma, Z.: Exploring hydrological- and environmental indicators with their coupled consequences on ecosystem services relationships for the riparian zones of Danube River Basin, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6007, https://doi.org/10.5194/egusphere-egu25-6007, 2025.

This work quantifies the hydrological alterations caused by climate change on 11 major basins of the Danube River. The quantification is performed using the natural discharge (i.e. without water demand and abstractions) between the years 1990 and 2020 as a reference period and the projected discharge between 2030 and 2100 for the SSP-RCP climate change scenarios SSP1-2.6, SSP3-7.0 and SSP5-8.5. Discharges for the reference period and the projections have been simulated with CWatM, a grid-based hydrological model. CWatM was calibrated and tailored for the Danube basin for this case study. The reference period was simulated using as input dataset hydrometeorological data from Multi-Source Weather (MSWX) product while the projected discharge was simulated using ISIMIP3b climate change hydrometeorological datasets for 5 global circulation models (GCM).

Past and future hydrological regimes were used to compute a set of indices from the Hydrological Nature Conservancy Indicators of Hydrologic Alteration. These indices quantify the in-stream disturbance regime and the average habitat conditions. Indices were computed using the discharge at the outlet of 11 Danube sub-basins. The differences between the reference and future hydrological regimes were assessed as percentage differences. The percentage differences were calculated for each combination of SSP-RCP—GCM, thus allowing to assess the uncertainty of the results.

The results show marked differences in the projected impacts for the different sub-basins. Overall, the basins in the lower course of the Danube are the most affected under all climate change scenarios, while those in the middle course are somehow more stable. Nevertheless, all sub-basins exhibit a moderate to strong hydrological alteration for at least two indices.

How to cite: Politti, E., Catania, C., Artuso, S., and Kahill, T.: Projected Hydrological Alterations in the Danube River Basin under Climate Change, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3743, https://doi.org/10.5194/egusphere-egu25-3743, 2025.

Water, an indispensable resource for sustaining life and ecosystems, is increasingly at the center of geopolitical tensions, particularly in transboundary river basins. This study introduces "Hydrocide" as a conceptual framework to analyze and address the deliberate manipulation of water resources that exacerbates socio-environmental vulnerabilities in downstream nations. Hydrocide captures the intersection of environmental injustice, resource governance, the root causes of disasters, and the socio-political dynamics of water management, framing such actions as a form of systemic oppression with long-term consequences. Rooted in the principles of the Universal Declaration of Human Rights, and no natural disasters, this framework reconceptualizes water crises as socially constructed phenomena, shaped by inequitable policies and governance rather than natural inevitabilities.

Using the Ganges-Brahmaputra-Meghna (GMB) basin as a case study, this work examines the implications of upstream water management practices, including dam and barrage construction, water diversion, and the absence of equitable transboundary agreements. The downstream impacts on Bangladesh, a riparian nation heavily reliant on these rivers, include seasonal water shortages, artificial floods, ecological degradation, and socio-economic instability. These challenges are compounded by the dual forces of climate change—such as glacier melt and extreme monsoonal rains—and population growth, which intensify demand and strain water availability.

The framework of "Hydrocide" offers a novel lens to conceptualize these challenges, bridging the discourse between environmental justice and global governance of shared water resources. This approach emphasizes the need for cooperative mechanisms, transparent data sharing, and equitable water distribution policies to mitigate the cascading impacts of hydrological mismanagement. By integrating hydrocide into transboundary water crisis management, this study aims to inform sustainable and fair solutions for one of the most vulnerable river basins in the world, while providing a transferable framework applicable to global contexts.

How to cite: Ahmed, B.: Hydrocide: A Conceptual Framework for Transboundary Water Crisis Management , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-569, https://doi.org/10.5194/egusphere-egu25-569, 2025.

Accurate water balance is important for both water resource management and nutrient emission modeling. This study compares the water balance results from the MONERIS (Modeling Nutrient Emissions in River Systems) model with those from WetSpass (Water and Energy Transfer between Soil, Plants, and Atmosphere under quasi-Steady State) and field-measured data in Hungary's Koppány basin, a 660 km² hilly catchment. MONERIS uses empirical equations of water balance components: precipitation, evapotranspiration, runoff, and groundwater recharge. WetSpass adds spatially explicit hydrological and land-use information. The most characteristic features of the Koppány catchment are a high proportion of agricultural land, large-field arable farming of approximately 63% of the total area of the catchment and total agricultural lands of 72% of the total area of the catchment, and relatively low population density of approximately 29 inhabitants per square kilometer (inh./km²).  The Koppany catchment has a mean annual flow of approximately 1.26 m³/s. Water quality is seriously affected by eroding soil conditions within the catchment and severe point-source contamination by wastewater effluents: treated wastewater makes up approximately 8% of the total flow.

The present study furthers nutrient emission modeling through showing the relative strengths and weaknesses of lumped empirical and spatially distributed process-based techniques.

Keywords: Water Balance, MONERIS, WetSpass, Koppány Catchment , Nutrient Emission modeling

How to cite: Almohtaseb, F. and Kardos, M.: Comparative Assessment of Water Balance Calculations: MONERIS and WetSpass Models in the Koppány Catchment, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9132, https://doi.org/10.5194/egusphere-egu25-9132, 2025.

Large-scale hydrological models simulate the water cycle for regions, countries, and continents. The choice of input data directly impacts the accuracy of these models' final output and the spatial and temporal pattern, as well as the quality of data (air temperature and precipitation), influences the quality and pattern of water availability estimates. It is essential to acknowledge that the accuracy of these estimates depends on the input quality of the data used.

In this regard, precipitation and air temperature gridded European Meteorological Observations (EMO1) datasets specifically used for hydrological modeling inputs (CWATM) are evaluated over the Danube River Basin (DRB). The observation data (air temperature and precipitation) from 9 different countries within the DRB are used for the EMO1’s evaluation.  The performance of the datasets was evaluated at daily, monthly, and annual scales, using Pearson Correlation (r), root mean square errors (RMSE), mean absolute errors (MAE), Nash Sutcliffe Efficiency (NSE), Percent Bias (PBIAS), and Kling Gupta Efficiency (KGE) criterion.

The results showed the range of temperature differences varies between approximately -3°C and +2°C. This reflects both underestimations and overestimations by EMO1 compared to observations. The median differences are close to 0 for most months, indicating the EMO1 model is generally unbiased or well-calibrated overall. Larger variability and more outliers occur in warmer months (e.g., May–August), suggesting the model may struggle with accurately capturing summer temperature dynamics. For precipitation, the median is slightly positive, suggesting a systematic overestimation of precipitation during the summer months. This could be due to the model overestimating convective rainfall. 

By identifying the periods where the EMO-1 deviates most from observations, researchers can target specific processes for calibration or refinement, which is especially important for hydrological  applications

Acknowledgment 

This work was supported as part of DANUBE WATER BALANCE, an Interreg Danube Region Programme project co-funded by the European Union.

How to cite: Amihăesei, V., Cheval, S., Chitu, Z., Radu, A., Petre, C., Ács, T., Kozma, Z., György, M., and Chendeș, V.:  Evaluation of European Meteorological Observations gridded data  of air temperature and precipitation amount over Danube River Basin (1990-2022) , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16995, https://doi.org/10.5194/egusphere-egu25-16995, 2025.