The development of global groundwater models and big-data assessments of groundwater wells have helped to push the boundaries of our large-scale understanding of groundwater processes. In particular, knowledge of the exchange between surface and subsurface waters is essential for determining the water balance at larger scales. Surface and subsurface water exchanges and inter-catchment groundwater flow affect water, pollutant, and nutrient fluxes, bio-organisms in streams, and the groundwater itself. Additionally, human activities (e.g., pumping/irrigation) increasingly affect groundwater flow processes and the exchange between surface and subsurface waters.
In this session, we want to highlight the increasing interest in the large-scale study of groundwater availability, quality, and processes (including groundwater recharge) and discuss current obstacles related to data availability and model design. Therefore, we seek contributions that address issues including:
* Continental to global groundwater-related datasets
* Regional to global big-data assessments with models and machine learning
* Transboundary and inter-catchment assessments of groundwater processes
* Identification of dominant controls on groundwater processes across large domains
* Recent methodological developments for the inclusion of small-scale hydrological processes into large-scale estimates
* Surface-subsurface water exchange and its effects on hydrological extremes (drought/flood), water availability, and solute and pollutant transport
* Effects of climate change, land use change, and water use change on global groundwater
* Implications of large-scale groundwater understanding on monitoring design, integrated water management, and global water policies
* Large-scale groundwater assessments related to the fulfillment of the UN sustainable development goals (SDGs)
Orals: Thu, 7 May, 16:15–18:00 | Room 2.15
Baseflow recession analysis provides direct insight into catchment-scale groundwater drainage behavior under low-flow conditions, when river discharge is predominantly sustained by subsurface storage. The recession time constant (K) is widely used to characterize groundwater drainage timescales and describe how catchments release stored groundwater. Although recent studies have applied this metric across regional catchments, the large-scale variability of K and the relative importance of environmental factors governing its spatial variability remain insufficiently constrained, particularly at the global scale. In this study, recession time constants were systematically estimated for global catchments spanning a broad range of climatic and geological settings, following the theoretical framework proposed by Brutsaert. Estimates were derived from baseflow-dominated recession segments extracted from long-term daily streamflow records, enabling a large-sample assessment of both the statistical properties and spatial variability of K across heterogeneous environments. The resulting distribution reveals pronounced clustering around characteristic timescales, while also exhibiting substantial spatial heterogeneity among catchments. The dominant controls on recession timescales were examined using an explainable machine-learning framework based on a LightGBM model combined with SHAP-based interpretation. Drainage porosity emerges as the most influential predictor of K, highlighting the central role of effective groundwater storage capacity in regulating baseflow recession duration. Hydraulic conductivity provides additional explanatory power, reflecting the importance of subsurface transmissivity, whereas soil thickness and drainage density exert secondary but still detectable influences through their effects on storage volume and flow-path organization. These results support a physically consistent interpretation of baseflow recession time constants as emergent properties of groundwater storage and drainage efficiency at the catchment scale. By clarifying the environmental controls on K across diverse settings, this study advances process-based understanding of groundwater–streamflow interactions and demonstrates the utility of recession analysis as a scalable approach for diagnosing subsurface hydrological behavior from widely available discharge data.
How to cite: Cheng, S. and Zhang, L.: Global patterns and controls of baseflow recession timescales from large-sample streamflow analysis, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9100, https://doi.org/10.5194/egusphere-egu26-9100, 2026.
Specific yield is an important parameter capturing sub-surface characteristics, such as grain size, shape, and pore distribution. Specific yield is used to estimate change in groundwater storage from groundwater levels. Hence, it is critical for estimating changes in groundwater availability, a critical resource for ensuring socioeconomic prosperity. At present the norm is to consider specific yield as a constant in time. In the present study, using the Gravity Recovery and Climate Experiment (GRACE) data based total water storage anomalies and quality controlled well observations at global scale (the United States, Europe, Australia, India, and China), we show that specific yield is not constant in time and varies with groundwater level. Further, we establish an exponential relation between groundwater levels and specific yield. The parameters (α = specific yield at zero groundwater level, β = rate of groundwater level decay) of the best fit exponential function are found to be the same across the United States (α= 0.17 ± 0.02, β= 0.02 ± 0.01 m-1), Europe (α= 0.11 ± 0.01, β= 0.03 ± 0.01 m-1), Australia (α= 0.12 ± 0.03, β= 0.02 ± 0.02 m-1), China (α= 0.11 ± 0.03, β= 0.05 ± 0.02 m-1), and India (α= 0.07 ± 0.02, β= 0.03 ± 0.03 m-1), within the uncertainty of the exponent. The methodology is validated using literature based specific yield values across the United States. In addition, improvement in modelling groundwater levels using AMBHAS-1D is observed when using a varying specific yield instead of a constant (NSE= 0.92, RMSE= 5.23 m). Hence, we conclude that with increased groundwater exploitation, its availability will drop faster than expected. Most of the regions investigated experienced a decline in specific yield over the last two decades, and the perceived groundwater availability for some locations is 80% less than that estimated using constant specific yield.
How to cite: Suryawanshi, M. R., Satish Kumar, K., Shaw, B., Varadaganahalli Anandagowda, C., Sukumaran, V., Kochar, A., Sekhar, M., Goswami, S., Chander, S., Nikam, B. R., Dasika, N. K., and Vishwakarma, B. D.: Dynamic specific yield explains accelerated groundwater loss, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11629, https://doi.org/10.5194/egusphere-egu26-11629, 2026.
Sustainable management of global groundwater resources is a key societal challenge and central to the Sustainable Development Goals. The localized impacts of groundwater abstraction and the subtle interaction with topography of groundwater dependent ecosystems call for high resolution groundwater information to support effective management. At the same time, groundwater observations are very limited and concentrated in a few countries, rendering large parts of the groundwater resources ungauged. To address limited observations and coarse global models, we use the global groundwater model GLOBGM to simulate past and project future groundwater heads and water table depth at 30 arc-seconds (~1 km) at a monthly time step. Using ISIMIP3a inputs, groundwater dynamics are simulated for a reference period (1960–2019) to support model evaluation and attribution of observed impacts to climate variability and change. Following ISIMIP3b, historical baselines (1960–2014) and three combined socioeconomic–climate scenarios (2015–2100; SSP1-RCP2.6, SSP3-RCP7.0, SSP5-RCP8.5) are simulated with five GCMs, supporting robust detection and impact assessment of future change. Regions of reduced reliability are mapped, and quality assurance flags are provided to guide appropriate use and interpretation of the results. The resulting dataset offers comprehensive, high-resolution information to assess groundwater dynamics for the past and future, supporting improved global water resource management and climate impact assessments.
How to cite: van Jaarsveld, B., Wanders, N., Otoo, N. G., Sutanudjaja, E. H., Verkaik, J., Zamrsky, D., and Bierkens, M. F. P.: Global hyper-resolution modelling of historical and future groundwater dynamics, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8890, https://doi.org/10.5194/egusphere-egu26-8890, 2026.
Although manganese (Mn) is an essential component of human nutrition, high levels of Mn consumption may be toxic. Despite most dietary Mn generally coming from food, Mn intake via drinking water sourced from groundwater can be substantial. With new evidence pointing to greater detrimental health effects, particularly for infants, from excess Mn in drinking water, the World Health Organization (WHO) lowered its health-based guideline for Mn in drinking water several years ago from 400 µg/L to 80 µg/L. With the new guideline value being just one-fifth of the previous one, we have employed machine learning to model Mn concentrations in groundwater globally in order to assess the implications of this change on affected regions and populations. This was done by first assembling a large dataset of groundwater Mn concentrations and relevant environmental parameters, which were then used in machine-learning modeling. Based on these results and considering national-scale rates of household use of unmanaged groundwater, we estimate that over 200 million people are at risk from consuming >80 µg/L Mn in drinking water, which happens to be about five times more than the 39 million people at risk based on the previous guideline of 400 µg/L. Although the number of people at risk due to high Mn in drinking water is comparable to that for arsenic and fluoride, Mn generally receives much less attention than do these other, also naturally occurring, groundwater contaminants. As such, the groundwater Mn hazard and risk maps produced in this study are important guides in helping identify safe groundwater sources.
How to cite: Podgorski, J. and Berg, M.: Global assessment of manganese in groundwater, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12235, https://doi.org/10.5194/egusphere-egu26-12235, 2026.
Groundwater nitrate (NO3-) pollution jeopardizes drinking-water safety under the UN’s Sustainable Development Goal 6. Recovery lags behind policy ambitions because legacy nitrogen (N) stored in the vadose zone creates a “long tail” of persistent contamination, where NO3- continues to leach for decades. Here, we integrate the “long tail” mechanism into a global N-balance model, and couple this enhanced model with 0.5° × 0.5° simulations to project centennial-scale NO3- dynamics (1961–2100) in groundwater systems worldwide. Our modeling suggests that by 2020, shallow aquifers had accumulated 162 ± 6 Tg N of NO3-, contaminating approximately 10% of global land area above the WHO drinking water safety limit (11.3 mg N L-1). More critically, a vast NO3- reservoir (4,037 ± 214 Tg N) in vadose zones sustains this long tail, which may generate new contamination hotspots over the next 80 years. Even with an immediate transition to zero-N-surplus, 4% of affected regions are projected to remain above the WHO limit beyond 2100. To guide effective governance, we classify global croplands into four management archetypes, from “no additional action” to “multi-generational remediation”, and propose tailored strategies balancing water quality, food security, and soil sustainability. Our findings redefine the temporal scope of environmental governance, highlight priority regions for targeted interventions, and provide a science-based roadmap for achieving safe groundwater within realistic socioeconomic constraints.
How to cite: Zhao, W. and Jia, X.: Vadose zone nitrogen legacy threatens achievement of global groundwater quality goals, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5606, https://doi.org/10.5194/egusphere-egu26-5606, 2026.
Groundwater levels are declining in many regions of Europe, raising concerns about long-term water security. However, sparse temporally continuous groundwater observations constrain our ability to fully understand the impacts of groundwater depletion, especially its socio-economic consequences. According to a recent report by the European Environment Agency, groundwater supplied around 28% of agricultural water in European Union Member States during the twenty-first century. This dependence highlights the vulnerability of European agriculture and the societies it supports to ongoing reductions in groundwater availability.
To understand the connection of socio-economic well-being, agriculture, and groundwater , we link a new 0.11° monthly water table depth anomaly dataset for Europe, spanning 1950 to the present, with existing European and global socio-economic datasets on crop production, crop prices and related agricultural indicators. This analysis enables us to assess how different crop types respond during periods of groundwater droughts. We examine long-term trends, identify crop-specific and region-specific sensitivities to groundwater decline, and evaluate how groundwater droughts propagate into market-level effects such as price fluctuations. Our results reveal distinct temporal and spatial patterns in both agricultural production and crop prices under groundwater stress, with some crops showing strong sensitivity to water table decline while others exhibit relative resilience. These findings provide a more nuanced understanding of the potential socio-economic risks associated with long-term groundwater depletion in a changing climate. Based on this study, we plan to provide recommendations for climate-resilient agricultural planning in regions facing persistent groundwater decline.
How to cite: Ma, Y. and Kollet, S.: Long-Term Socio-Economic Consequences of Groundwater Depletion Under Climate Change, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8201, https://doi.org/10.5194/egusphere-egu26-8201, 2026.
Reliable prediction of groundwater behaviour is essential for sustainable water resource management, particularly as climate variability intensifies pressure on subsurface reserves. Richards' equation provides a physically rigorous description of water movement through both unsaturated and saturated zones, yet its computational demands have long precluded application at continental scales.
Here we present a novel three-dimensional solver for Richards' equation built on Firedrake, a flexible finite element framework. This approach enables simulation of groundwater dynamics across spatial scales ranging from metres to thousands of kilometres, bridging the gap between local process studies and regional water management.
We demonstrate the solver through a case study of the Lower Murrumbidgee basin in Australia, encompassing approximately 3600 km². The simulation assimilates observational data from the Bureau of Meteorology, including basin stratigraphy comprising three layers of varying depth, annual rainfall estimates, and present-day water table depths. Our results capture decadal-scale flow dynamics at spatial resolutions previously unattainable for basins of this size. This work addresses critical limitations in current operational approaches, which do not fully couple unsaturated and saturated flow processes, and offers a pathway toward improved hydrological forecasting and water resource assessment at regional to continental scales.
How to cite: Ghelichkhan, S. and Morrow, L.: Data-Driven Modelling of Large-Scale Groundwater Dynamics, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21017, https://doi.org/10.5194/egusphere-egu26-21017, 2026.
The Ganga River basin has been subject to increasing water stress in recent decades. Due to an increase in anthropogenic activities and climate factors, the terrestrial water storage of this basin is affected. Traditional groundwater monitoring using observation wells often fails to represent basin-scale spatial and temporal variability of groundwater storage due to the sparse distribution of monitoring wells. Satellite-based remote sensing provides an effective alternative in regions with limited in-situ data. In the present study, the Gravity Recovery and Climate Experiment (GRACE) data are used for a large-scale assessment of terrestrial water storage (TWS) variability in the Ganga basin for the period 2003–2024. The Groundwater Storage Anomalies (GWSA) are estimated by removing the soil moisture, snow water equivalent, and canopy water storage components available through the Global Land Data Assimilation System (GLDAS) from the TWS anomalies. Precipitation characteristics, basin-scale hydrogeological and topographic properties, are used to interpret the observed spatio-temporal variability in groundwater storage. Furthermore, basin-scale evapotranspiration, associated baseflow, and runoff are analysed using GLDAS products, and by combining them with GRACE-based observations, the interactions between surface water fluxes and subsurface storage variability are obtained. Results indicate a persistent decline in groundwater storage, accompanied by high evapotranspiration and reduced baseflow, which leads to increasing groundwater stress, potentially influenced by anthropogenic water use. Groundwater exhibits a lagged and damped response to precipitation, reflecting a delayed recharge process in the basin. Enhanced evapotranspiration are observed during dry and pre-monsoon periods. Finally, soil moisture and groundwater drought characteristics in the basin, derived from standardised storage anomalies, are used to assess spatio-temporal groundwater stress conditions and thereby water-stressed hotspots are identified in the Ganga basin.
Keywords: GLDAS, GRACE, Groundwater Storage Anomalies, Groundwater stress.
How to cite: Pathak, A. and Pathania, T.: Evaluating the spatio-temporal groundwater stress with data-driven models and satellite data for the Ganga River Basin., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10369, https://doi.org/10.5194/egusphere-egu26-10369, 2026.
Groundwater provides a critical freshwater resource for agriculture, industry, and drinking water across North America. However, the long-term impacts of climate variability and change on groundwater availability remain poorly constrained at continental scales. Here, we evaluate how changing climate variability impacts North American groundwater table depths under three different future climate scenarios. We use the Water Table Model (WTM), a large-scale, physically based hydrological model, to simulate depth to water table at an annual scale from 1800 to 2100 CE. The model is forced by changing precipitation and evapotranspiration based on climate simulations and data from TraCE-21ka (past), CMIP6 (historical and future), and Terraclimate (present). Model results for the historical period (1800–2015) are evaluated against available lake, wetland, and groundwater well observations. Based on this, we find patterns of historical groundwater variability across North America. We then quantify spatial and temporal changes in depth to groundwater and identify regions of long-term groundwater stability, rise, or decline in response to climate forcing under three future scenarios (SSP1-2.6, SSP2-4.5, and SSP5-8.5). Our results reveal strong regional heterogeneity, with relatively stable or rising groundwater levels in humid and high-latitude regions, in contrast to persistent declines in arid and semi-arid zones. Future groundwater availability depends strongly on the emission scenario simulated, highlighting increasing climate-driven groundwater vulnerability across large parts of North America. This work provides a novel, annually resolved, continental scale assessment of climate impacts on groundwater availability and offers valuable insights for large-scale water balance studies, drought assessment, and sustainable groundwater management under a changing climate.
How to cite: Haghiri, M., Callaghan, K., Creel, R., Austermann, J., and Wickert, A.: Climate-Driven Changing Groundwater Depth across North America, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15769, https://doi.org/10.5194/egusphere-egu26-15769, 2026.
Nile downstream countries, particularly Egypt, which depend on the Nile as their primary water resource, face a water budget deficit due to increasing consumption, hydroclimatic changes, and upstream damming (i.e., the Grand Ethiopian Renaissance Dam (GERD)). To address these challenges, Egyptian authorities introduced new management strategies for the High Aswan Dam Reservoir (HADR), the third largest artificial reservoir globally, is proposed to develop new agricultural areas. However, the interconnectivity between the HADR and the fossil Nubian aquifer, Africa's largest transboundary aquifer, remains speculative due to a lack of in situ investigations. To address this gap, we constructed a hydrogeological flow model to simulate HADR-Nubian Aquifer interaction under various upstream damming operation and flow condition scenarios, using the Moldflow model, incorporating geological, geophysical, and hydrogeological data. Our results indicate that the water-saturated normal faults serve as preferential flow pathways connecting the HADR to the Nubian Aquifer, potentially facilitating bidirectional water exchange depending on relative hydraulic head gradients. Our findings underscore forthcoming challenges for this linkage if the level of the HADR falls below approximately 160 m above mean sea level due to unmanaged upstream damming operations during the Nile’s extended drought periods. Under these conditions, the Nubian Aquifer's pressure head could surpass the HADR's reservoir head, resulting in aquifer discharge back into the HADR. This would alter the aquifer's water budget and compromise the planned agricultural developments in the adjacent areas, which constitute approximately 10% of Egypt's total arable land. These findings support a cooperative transboundary water management agreement that considers maintaining HADR water levels above critical thresholds to ensure both agricultural development and long-term aquifer sustainability across the Eastern Nile Basin.
How to cite: Ramah, M., Heggy, E., and Hanert, E.: Investigating the Interaction Between the High Aswan Dam Reservoir and Nubian Aquifer Under Increasing Nile Upstream Damming, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17083, https://doi.org/10.5194/egusphere-egu26-17083, 2026.
Posters on site: Thu, 7 May, 14:00–15:45 | Hall A
Groundwater systems in headwater catchments are poorly represented at continental scales due to model resolution constraints and limited observations available to characterize the wide diversity of catchments. Yet, low-order headwater streams accounting for a major fraction of the global river network. This is particularly true in upland crystalline bedrock regions with dense drainage networks, where the lithology has long been considered impermeable, without aquifers, and thus has received limited hydrogeological attention.
We present a new continental-scale assessment of effective transmissivity for 3,333 European crystalline headwater catchments (median ≈35 km²), underlain by unconfined, shallow hard-rock aquifers where subsurface-surface interactions strongly shape hydrological connectivity. Catchments including dams, glaciers, and extensive permafrost were excluded.
The methodology represents lateral hillslope groundwater flow within shallow subsurface systems, capturing the spatial patterns of saturated areas at the catchment scale. This framework of physically based groundwater flow models enables steady-state simulation of perennial surface water networks (springs, streams, wetlands), whose length and structure are highly sensitive to shallow aquifer transmissivity (Abhervé et al., 2023). Transmissivity was inferred through optimization of simulated seepage areas against observed wetland and stream networks, using constant recharge estimates from an independent land surface model and assuming dominant superficial subsurface flow in the upper 50 m. Across all calibrated models, the simulated networks closely replicate the available European-scale extended wetland ecosystem layer and stream network from the EU-Hydro database.
Estimated transmissivity ranges from 10⁻⁸ to 10⁻² m² s⁻¹ (mean ≈10⁻⁴ m² s⁻¹), with pronounced spatial variability across geological provinces, massifs, or regions sharing similar tectonic framework legacies. The broad transmissivity range demonstrates the method’s sensitivity and its ability to resolve catchment-scale effective hydraulic properties across diverse climatic, topographic, and geological contexts. Values are consistent with textbook estimates for the studied lithologies and with hydraulic test data (pumping and slug tests) from regional or global datasets. Both measurements and estimates follow a log-normal distribution. Hydraulic conductivity was also derived from transmissivity using independent aquifer thickness datasets, including global depth-to-bedrock and regolith thickness maps.
Our results provide the first EUropean crystalline bedRock hydrogeological HEADwater map of transmissivitY (EURHEADY), explicitly accounting for groundwater flows at the catchment scale. All calibrated simulations are provided as a georeferenced dataset, complemented by physiographic, climatic, hydrologic, pedologic, geologic, hydrogeologic, and anthropogenic attributes. This approach addresses a critical gap in estimating hydrogeological properties, a long-standing challenge for the critical zone community, and opens new opportunities for large-scale hydro(geo)logical modeling with improved representation of groundwater contributions.
Reference:
Abhervé, R., Roques, C., Gauvain, A., Longuevergne, L., Louaisil, S., Aquilina, L., & de Dreuzy, J. (2023). Calibration of groundwater seepage against the spatial distribution of the stream network to assess catchment-scale hydraulic properties. Hydrology and Earth System Sciences, 27(17), 3221–3239. https://doi.org/10.5194/hess-27-3221-2023
How to cite: Abhervé, R., Gauvain, A., Dupas, R., Bresciani, E., Boisson, A., Marçais, J., Salmon-Monviola, J., Durand, P., Squividant, H., Fovet, O., Delottier, H., Brunner, P., Longuevergne, L., Aquilina, L., de Dreuzy, J.-R., and Roques, C.: A pan-European map of shallow aquifer transmissivity in crystalline headwater catchments inferred from wetland and stream networks, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5064, https://doi.org/10.5194/egusphere-egu26-5064, 2026.
In catchments characterised by complex hydrological regimes, where streamflow is derived from significant groundwater contributions alongside diverse surface and anthropogenic inputs, accurate process representation is crucial. To address this challenge, this study presents a novel coupling of the Water System Integrated Modelling Framework (WSIMOD), which simulates water quality and quantity across the urban-rural integrated catchment, with the fully distributed groundwater model MODFLOW. The coupled framework is evaluated in the Upper River Lee catchment (UK), specifically focusing on two sub-catchments with distinct hydrological characteristics. To ensure a robust evaluation, the standalone WSIMOD, standalone MODFLOW, and the coupled model were all calibrated automatically using the PEST. While all three model configurations demonstrated satisfactory performance, the coupled model exhibited superior predictive capability, particularly regarding baseflow and groundwater levels. The study highlights the distinct added value of this hybrid approach. Compared to WSIMOD alone, the coupled model captures local spatial variations in groundwater and river dynamics, which is vital for investigating groundwater abstraction impacts. Conversely, relative to standalone MODFLOW, the coupled model provides a more detailed representation of surface water processes, specifically capturing the complex influence of urban infrastructure on the catchment’s hydrology. These results demonstrate that coupling lumped and distributed models is effective for resolving the complex water cycle dynamics of human-impacted catchments.
How to cite: Zong, W.: Coupling WSIMOD and MODFLOW to Enhance the Representation of Groundwater-Surface Water Interactions in Complex Catchments, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7577, https://doi.org/10.5194/egusphere-egu26-7577, 2026.
Bangladesh, one of the most densely populated countries in the world, relies primarily on its irrigated agriculture to sustain rice production for a population that rose from 90 million in 1981 to about 165 million in 2022. Consequently, over the past three decades, irrigated land in Bangladesh has expanded from 2.58 million ha in 1990 to approximately 5.63 million ha in 2020, increasing the share of irrigated land from 31% to 66%. This rapid expansion has relied heavily on shallow groundwater abstraction, which, together with increasing domestic and industrial abstraction, has led to declining groundwater levels, altering the river-aquifer exchange in the Bengal Delta. Previous studies have estimated the overall change in the total groundwater recharge associated with increased abstraction through freshwater capture (“Bengal Water Machine”). However, these studies have not quantified the change in the focused recharge from river leakage into the groundwater system. To address this issue, we have developed a numerical groundwater flow model to assess the impact of increasing abstraction over the past four decades on the river-aquifer interactions in the North-central Bangladesh.
The 3D unstructured numerical model domain (area: 27670 km2) is delimited by the Shillong Plateau (i.e., Precambrian basement) to the north, and by the Brahmaputra (locally known as Jamuna), Meghna, and Ganges (locally known as Padma) rivers, to the west, east and south, respectively. The groundwater flow model was implemented in MODFLOW-6 and was set up using Flopy environment. The flow model consists of 11 layers (370 m average thickness) based on a regional geological model developed from borehole lithological data, and reflecting the multilayer aquifer distribution described in the literature. Main river networks within the study area, direct (diffuse) recharge from effective precipitation, and abstraction for domestic, irrigation, and industrial purposes were considered as boundary conditions. River-aquifer exchanges were simulated using the RIV package, driven by long-term monthly stage observations at several fluviometric stations within the domain. Hydraulic properties including hydraulic conductivities, vertical anisotropies, and specific storage, along with the riverbed conductance were calibrated using PEST++, based on long-term groundwater levels and drawdowns between 1980 and 2018 in over 80 observation wells located within the model domain.
The preliminary results show that the steady increase in groundwater abstraction for irrigation, especially using wells located in the shallow aquifer, has reversed the direction of flow in most rivers compared to the pre-irrigation (i.e., natural) condition, changing the hydrological system from gaining to losing regime. The magnitude of these changes is subject to high uncertainty, due to the intrinsic heterogeneity of the aquifer system and to the conductances in the riverbed, the morphology of the channels and other factors, especially during the monsoon (wet season).
How to cite: Zolezzi-López, J., Muñoz-Vega, E., Shamsudduha, M., and Schulz, S.: Spatio-temporal changes of river-aquifer interactions in North-central Bangladesh, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9966, https://doi.org/10.5194/egusphere-egu26-9966, 2026.
Wetlands are recognised as one of the most important ecosystems in terms of their unique biodiversity. Yet since 1900, the world has lost more than 50% of its wetland area (Davidson, 2014; Dugan, 2005; Winkler & DeWitt, 1985). Groundwater dependent wetlands (GDWs) provide critical ecological functions but face increasing pressure from climate variability and groundwater abstraction, while their global extent and dynamics remain poorly quantified. Here we present the first spatially and temporally explicit global assessment of GDW extent using a high resolution, physically based groundwater modelling framework.
We developed a dynamic GDW mapping framework based on GLOBGM global groundwater model (Verkaik et al. (2022), a 30 arc second, two-layer MODFLOW model, coupled offline with PCR-GLOBWB (Sutanudjaja et al., 2018). We include improved recharge estimates through bias correction and enhanced groundwater-surface water coupling via dynamically updated drainage elevation using saturated area fraction to better represent shallow groundwater processes.
Following ISIMIP3a and ISIMIP3b protocols, we simulated monthly groundwater conditions from 1960 to 2014 and projected changes up to 2050 under SSP1-2.6, SSP3-7.0 and SSP5-8.5 using five CMIP6 global climate models per scenario (Lange & Büchner, 2021). Evaluation of groundwater heads against more than 15000 wells from the IGRAC dataset (IGRAC, 2024) show strongest performance for shallow water tables (average depth less than 5m) with about 67 % of wells with Kling Gupta Efficiency KGE ≥ −0.41.
Following earlier work (Otoo et al., 2025), we identified GDWs as areas with a saturated area fraction greater than 0.5 and water table depth less than or equal to 5 m, capturing both core groundwater fed wetlands and peripheral drought adapted systems while accounting for sub-grid variability. We exclude areas where groundwater results remain unreliable due to spin up issues, karst, permafrost and mountain areas (in total, only about 19 % of global areas). This approach shows strong spatial agreement with independent datasets, achieving a global hit rate of 76 % against the Global Lakes and Wetlands Database 2 (GLWD 2) (Lehner et al, 2025), and exceeding 80 % against the Australian Atlas (Doody et al., 2017).
We also account for land conversion when simulating area changes by excluding potential GDWs that coincide with agricultural areas in PCR-GLOBWB (rainfed and irrigated agriculture and pasture) for both past and future periods. For the historical period, we attributed groundwater level trends to climate-driven recharge changes, human-driven groundwater abstraction or a combination of both and quantified GDW area changes aggregated by WWF biome realm units (Olson et al., 2001). Preliminary results show strong reductions of past and future wetlands in Afrotropical, Indo-Malayan and Neotropical regions with distinct areas where either groundwater level decline or land use change are the dominant drivers. This framework addresses a major gap in global wetland assessments and provides a physically groundwater basis for evaluating past and future GDW dynamics in support of conservation planning, climate impact assessment and policy development aligned with Ramsar Convention, the Sustainable Development Goals and global biodiversity targets.
How to cite: Otoo, N. G., Jaarsveld, B. V., Sutanudjaja, E. H., van Vliet, M. T. H., Schipper, A. M., and Bierkens, M. F. P.: The impact of climate change, land use change and groundwater extraction on groundwater-dependent wetlands extent worldwide, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11264, https://doi.org/10.5194/egusphere-egu26-11264, 2026.
The Indo-Gangetic Basin (IGB) is a large trans-boundary aquifer system encompassing the alluvial Indo-Gangetic Plain (IGP) as well as the southern parts of the Indus, Ganges and the Rajasthan Inland drainage basin, supporting a large agrarian population. In recent decades, expansion of groundwater irrigation through shallow-medium tubewells (<70m) has boosted crop yields by reducing reliance on monsoon rains, enabling India to achieve food security and improving the livelihoods of millions. Although the IGP now accounts for around 25% of global groundwater abstraction, groundwater use in many parts of the wider IGB remains unsustainable and has driven widespread depletion. However, the Indo-Gangetic basin is not a single hydrogeological unit but a complex and heterogeneous aquifer system that is responding differently to the various pressures, including groundwater abstraction for irrigation and climate variability. Here, we analyse a groundwater well dataset to characterise the long-term patterns and trends in groundwater resources in the IGB for the time period 1998-2024, and improve our understanding of how the groundwater system interacts with various hydro-meteorological and anthropogenic factors. We compiled a new quality-controlled dataset of quarterly groundwater well data in the IGB which includes quarterly water level data for 5877 unique wells in the region. Our dataset also includes meteorological and land use data from various sources. Mann–Kendall trend analysis of groundwater levels between 1998–2010 across 2,585 wells indicates predominantly negative trends across the Indo-Gangetic Basin. These patterns can be attributed to intensification of the use of deep tubewells (>70m) in the Rajasthan Inland drainage basin and the Indus basin and shallow-medium tubewells in the Ganges basin during this period. Post-2010, we show that groundwater levels have shifted from a declining trend to a more stable trend in the Ganges basin overall. Nevertheless, in the north-west Ganges basin, Indus basin and Rajasthan inland drainage basin, despite experiencing increased rainfall and an extended multi-annual wet anomaly, groundwater levels continue to decline post-2010. The rate of decline has stabilised in the Indus basin but continues to increase in Rajasthan Inland drainage basin. In the Central Ganges basin, the trend shifts from a declining trend pre-2010 to a positive trend with rising groundwater levels. Groundwater levels in south-western parts of the Ganges basin that were stable between 1998-2010 now show a rising trend. The Minor Irrigation Census indicates no significant increase in the number of shallow–medium and deep tubewells across the Indo-Gangetic Basin between 2014 and 2017. However, land use inventory data for 2014–2024 show an expansion of cropped area in the Rajasthan Inland Drainage and Indus basins, along with an overall increase in the area sown more than once across the IGB. These patterns suggest that changes in agricultural practices, crop types and cropping patterns across sub-basins are contributing to long-term groundwater trends and variability in the region. Our results reveal pronounced, scale-dependent heterogeneity in the response of the IGB to climatic, environmental and anthropogenic stressors.
How to cite: Mishra, P., Moulds, S., MacAllister, D. J., Scheidegger, J., and MacDonald, A.: Spatially Contrasting Groundwater Trajectories in the Indo-Gangetic Basin., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11646, https://doi.org/10.5194/egusphere-egu26-11646, 2026.
Decline in groundwater levels has induced severe socio-economic consequences globally. These include water scarcity, land subsidence, and salinization of arable land. However, the capability of current Global Water Models (GWMs), including H08, to simulate groundwater level declines is still limited, partly because the groundwater, especially the lateral flow processes, used to be downplayed. A recent effort has been made to enable explicit representation of groundwater level and lateral flows in H08. The newly developed model is named as H08-GMv1.0 but has previously only been validated in terms of steady-state simulation. Here, we present the monthly transient simulation results from H08-GMv1.0 during 1979-2019, validated by ~20,000 USGS monitoring wells. The Theil-Sen trend of global groundwater level demonstrates severe decline in major aquifer systems worldwide. The results also show that in several irrigation intensive systems, i.e., High Plains aquifer, Indus River Basin aquifer, and Northern China Plain, the human groundwater pumping is the main cause for groundwater level declines, which calls for urgent and coordinated groundwater governance and demand-side management interventions.
How to cite: He, Q., Hanasaki, N., Matsumura, A., Sutanudjaja, E., and Oki, T.: Human-induced global groundwater decline simulated by H08-GMv1.0, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15402, https://doi.org/10.5194/egusphere-egu26-15402, 2026.
Geogenic salinisation threatens groundwater in the German State of Brandenburg, where 25% of drinking water aquifers are already affected. The source are deep-seated brines originating from Upper Permian (Zechstein) salt dissolution, migrating upward via structural flow paths. The Oligocene Rupelian Clay isolates freshwater aquifers, but Quaternary glacial erosion created localised "windows" filled with permeable sands, enabling saline water ascent. Climate change drives declining groundwater recharge (GWR) in Brandenburg, projected to worsen and, coupled with extraction, increasingly compromise the freshwater-saline interface. Understanding the interplay between erosion windows, reduced recharge, and extraction is paramount for sustainable water management in this climate-vulnerable region.
A high-resolution 3D density-dependent flow and transport model is developed and employed using the Geomodelator-GUI [1] and TRANSPORTSE software [2] to investigate salinisation mechanisms in Brandenburg’s Lower Spree catchment area. The 3D framework integrates detailed hydrostratigraphy, capturing complex window geometry and anisotropic flow, assessing preferential pathways and clay barrier efficacy. Simulations assess four 100-year scenarios: (i) a Zero-Extraction Baseline, ZE, (ii) a Constant Recharge Baseline, CR, (iii) a Uniform Recharge Decline, UR, (linear 42% GWR reduction by 2050), and (iv) a Differential Recharge Decline, DR (spatially variable reductions: -20% to -60% in recharge/depletion zones). The model incorporates seven waterworks and utilises strata-specific porosity and hydraulic conductivity parameters derived from regional studies. Maximum salt concentrations are 10 g/L below the Rupelian.
Results demonstrate increased salinisation from upwelling under reduced recharge and extraction, particularly in deeper Tertiary aquifers and Quaternary window sediments itself. UR causes the highest intrusion: salt concentrations increase by 17% (9.6 mg/L) in the erosion windows. DR reduces intrusion by maximum 38% vs. UR at 100 years, but deep aquifers remain critically vulnerable. Shallow aquifers show minor changes (from an initial 0.1 mg/L to 0.17 mg/L), indicating salinisation predominantly affects deeper aquifers. Critically, even constant recharge with extraction drives salinisation, proving that groundwater extraction over long time periods is a decisive factor that is exacerbated by GWR decline.
3D model outcomes have elucidated critical processes inaccessible to 2D approaches [3] and provide an essential scientific foundation for proactive water resource management in Brandenburg and analogous basins. Results will directly support strategies to mitigate salinisation risks, such as adjusting sustainable extraction rates under future climate scenarios, and prioritising areas for enhanced monitoring or managed aquifer recharge. As subsurface utilisation for energy storage increases, this work also offers insights for safeguarding freshwater resources from potential deep brine mobilisation. Ultimately, the study underscores the urgency of integrating climate adaptation and detailed subsurface characterisation into groundwater governance to secure freshwater supplies in the face of escalating geogenic and anthropogenic pressures.
References:
[1] Kempka, T. et al. (2026, in review): GEOMODELATOR-GUI: A Web-Based Graphical User Interface for 3D Geological Modeling. SoftwareX.
[2] Kempka, T. (2020): Verification of a Python-based TRANsport Simulation Environment for density-driven fluid flow and coupled transport of heat and chemical species, doi: 10.5194/adgeo-54-67-2020.
[3] Chabab, E. et al. (2022): Upwelling mechanisms of deep saline waters via Quaternary erosion windows considering varying hydrogeological boundary conditions, doi: 10.5194/adgeo-58-47-2022.
How to cite: Chabab, E., Kühn, M., and Kempka, T.: Climate-driven groundwater recharge decline as a potential accelerant of geogenic salinisation in Brandenburg: A regional-scale 3D hydrogeological modelling study, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19362, https://doi.org/10.5194/egusphere-egu26-19362, 2026.
This study evaluates the complex hydrogeological conditions of the Amyntaio Basin by synthesizing historical data with updated 2021 piezometric measurements. The region’s geological framework is defined by intense neotectonic activity and lithological anisotropy, resulting in a system of overlapping granular aquifers—unconfined, leaky, or confined—that exhibit complex hydraulic behaviors.
The Groundwater aquifers of Amyntaio-Florina and Perdikka-Filota are categorized as having "Poor" quantitative status under EU Water Framework Directive criteria. While industrial dewatering associated with Public Power Corporation Lignite Mining has decreased since 2018 and stopped in may 2020, the basin remains under significant stress due to sustained abstractions for irrigation and municipal supply. The research indicates that the basin's response deviates from classical porous media models due to the presence of hydraulic boundaries and fault-controlled lateral recharges.
A critical re-evaluation of the monitoring network revealed that historical data (pre-2021) often lacked the resolution to distinguish between distinct aquifer horizons. The integration of deep-seated piezometers (>200m) into the 2021 network facilitated a high-fidelity mapping of the piezometric surface. Findings indicate that the hydraulic influence of mine dewatering is characterized by a high hydraulic gradient but a limited spatial radius, typically restricted to a zone of 500–800m from the mine’s crest.
The investigation into ground fissures and land subsidence in the settlements of Valtonera, Fanos, and Rodonas suggests a multi-causal mechanism, almost independent of mining activities:
- Lithological Vulnerability: Settlements are founded on Holocene deposits with poor geomechanical properties.
- Piezometric Drawdown: Localized intensive irrigation creates discrete cones of depression, often deeper than those observed near the industrial fronts.
- Peat Oxidation and Consolidation: Following the historical reclamation of the Chimaditida marsh (1960s), the aeration of organic-rich horizons initiated biochemical oxidation. This process, coupled with the loss of buoyancy in the drained peat layers, has resulted in sustained, long-term volumetric shrinkage and surface deformation.
- Tectonic Control: Major fault systems (e.g., Petron-Sklithro) act as planes of weakness, facilitating differential subsidence and aseismic creep.
In conclusion, the environmental degradation in the Amyntaio Basin is a long-term process governed by a synergy of tectonic constraints and initiated by marsh drainage and century-long anthropogenic interventions. The limited recovery potential of the aquifers, particularly in zones distal to the primary recharge points (Sklithro and Rodonas streams), necessitates a specialized management strategy that accounts for the basin's compartmentalized hydraulic behavior.
How to cite: Skourtsos, E., Filis, C., Andreadakis, E., Kapourani, E., Kranis, H., Roumpos, C., Kostaridis, P., and Louloudis, G.: Hydrogeological Complexity and Ground Fissures in the Amyntaio Basin: The Role of Tectonics and Anthropogenic Interventions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19708, https://doi.org/10.5194/egusphere-egu26-19708, 2026.
The increasing demand of Li, required in the electrification of motoring industry, has intensified the exploitation of brines in salt flats, as one of the main known sources of this element. Continental salt falt are hydrogeological systems characterized by extreme salinity gradients that generate significant spatial variations in groundwater density and give rise to complex flow patterns dominated by thermohaline circulation. Despite their relevance, density-dependent processes are often simplified or neglected in hydrogeological models used to assess brine exploitation, introducing substantial uncertainty in the interpretation of system behavior and associated impacts.
In this contribution, a coupled numerical modelling approach is presented to analyze the hydrogeological response of a salar subject to brine exploitation under variable-density flow conditions. First, a three-dimensional regional-scale groundwater model was developed and calibrated against observed hydraulic heads and salinity distribution. The model represents basin-scale flow patterns and incorporates existing brine pumping associated with exploitation, providing a reference framework for evaluating anthropogenic perturbations.
Building on the calibrated regional model, the system response to a controlled brine injection test associated with Direct Lithium Extraction (DLE) schemes was investigated. The simulations allow assessment of the spatial and temporal evolution of the injected brine plume, as well as the interaction between pumping- or injection-induced hydraulic gradients and buoyancy forces related to density contrasts
Results indicate that both brine extraction and reinjection induce non-linear and spatially propagated responses that are strongly controlled by density contrasts and hydrostratigraphic architecture, and that differ markedly from predictions obtained using constant-density approaches. The study highlights the necessity of explicitly accounting for density-dependent flow when evaluating the impacts of brine exploitation and reinjection strategies, and provides a physically consistent modelling framework to support the assessment and management of salars under conventional and DLE schemes. Those models would help to predict not only the evolution of phreatic level in a strategy based on DLE, but also would predict groundwater flow paths and the stability of the freshwater–brine mixing zone in marginal areas.
How to cite: Jurado Duarte, D., Valdivieso, S., Crisóstomo, B., Concha_Dimas, A., Vázquez-Suñé, E., and Carrero, S.: Density-dependent groundwater flow and hydrogeological response to brine extraction and reinjection in salt flat, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18523, https://doi.org/10.5194/egusphere-egu26-18523, 2026.
Groundwater is the main source of fresh water on Earth. It provides drinking water, supports agriculture, and sustains ecosystems. During droughts, this subsurface reservoir also maintains river flow through baseflow. Groundwater systems can buffer temporal fluctuations in recharge and moderate the severity of both short-term dry spells and prolonged droughts.
In this study, we investigate the recession behavior of baseflow of European catchments during periods of droughts assuming a non-linear storage-baseflow relationship. We focus on two key parameters: the recession constant (k) and the nonlinearity exponent (n). Using a large set of recession segments, we show that the duration of the recession period strongly influences the parameter estimation. In particular, the degree of nonlinearity strongly depends on the length of the recession periods. Short recession periods (<1 month) show a stronger degree of nonlinearity than longer ones. For very long recession periods of about a year the nonlinearity exponent approaches 1 indicating a linear relationship between storage and baseflow.
In order to explain these findings, we develop a theory based on the assumption that regional groundwater systems contributing to baseflow are spatially heterogeneous. To that end, different parts of the groundwater system contribute with a different recession behavior to the total baseflow. Based on stochastic theory, we derive an effective nonlinear-storage-baseflow relationship which links statistical properties of a groundwater systems with the recession constant (k) and the nonlinearity exponent (n). Using our theory, we can explain why the estimated degree of non-linearity depends on the length of the recession period.
Our results emphasize the importance of the length of selected recession periods in the characterization of non-linear storage-baseflow relationships. We will discuss how to make use of this finding and propose to use a spectrum of different recession periods to get more information on the spatial heterogeneity of groundwater systems contributing to baseflow.
Moreover, we will discuss the relevance of spatial heterogeneity of regional groundwater systems on buffering short and long term hydrological droughts.
How to cite: Ibourichene, A. and Attinger, S.: Linking Regional Aquifers Heterogeneity with Nonlinear Storage-Baseflow Relationships for European Catchments, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19300, https://doi.org/10.5194/egusphere-egu26-19300, 2026.
Accurate representation of baseflow remains challenging in within-grid large-scale hydrologic models, where groundwater is often represented as a single storage compartment per grid cell that exchanges water only vertically with the overlying soil column, without lateral groundwater flow between neighboring cells. Here we test how groundwater formulation, infiltration physics, and calibration strategy control baseflow skill in the mesoscale Hydrologic Model (mHM) [1]. We systematically compare two within-grid groundwater schemes (the linear scheme originally implemented in mHM and an exponential scheme newly implemented following Niu et al. [2]) and two soil infiltration representations (infiltration capacity and the one-dimensional Richards equation [3]) across 200 catchments in Germany. We use individual-basin calibration to quantify the best achievable performance of each model variant and multi-basin calibration to test parameter transferability and identify a single German-wide parameter set. Parameters are estimated within the Multiscale Parameter Regionalization (MPR) framework [1], and the baseflow index (BFI) is explicitly included in a joint calibration discharge (Q) and baseflow index (Q+BFI).
Including the baseflow index in calibration substantially improves long-term runoff-baseflow partitioning and daily baseflow dynamics, while maintaining the performance for streamflow, evapotranspiration, soil moisture, and terrestrial water storage anomalies. Incremental calibration experiments further show that baseflow skill in exponential formulations commonly used in SIMGM- and TOPMODEL-type approaches is primarily controlled by two parameters that are often prescribed as fixed values: the decay rate f and the maximum baseflow QBx. Calibrating only f improves baseflow markedly, while calibrating only QBx yields smaller gains. Calibrating both is required for reliable baseflow dynamics.
Across both individual-basin and multi-basin calibrations, the exponential groundwater scheme reproduces the weakest baseflow performance. This deficiency can be attributed to the absence of an explicit response time scale: the scheme reacts either too rapidly or too slowly to recharge variations, and therefore fails to capture observed baseflow behavior. To address this, we introduce a single damping parameter that represents a groundwater response time scale, analogous to the delay process that is explicitly represented in linear groundwater formulations. We refer to this modified formulation as the damped-exponential scheme. Introducing this damping markedly improves baseflow performance and yields comparable performance to the linear formulation at both basin and Germany-wide scales. The improvement is not limited to streamflow partitioning: the damped-exponential scheme also better reproduces groundwater dynamics, supported by comparisons of water-table depth variability at 118 monitoring wells across Germany.
References:
[1] Multiscale parameter regionalization of a grid‐based hydrologic model at the mesoscale. Water Resources Research 46 (2010), 10.1029/2008WR007327.
[2] Development of a simple groundwater model for use in climate models and evaluation with Gravity Recovery and Climate Experiment data. J. Geophys. Res. 112 (2007), 10.1029/2006JD007522.
[3] Evaluating Richards Equation and Infiltration Capacity Approaches in Mesoscale Hydrologic Modeling. Water Resources Research 61 (2025), 10.1029/2024WR039625.
How to cite: Kholis, A., Attinger, S., Kalbacher, T., and Samaniego, L.: Improving baseflow in within-grid large-scale hydrologic models through a groundwater response-time scale, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9445, https://doi.org/10.5194/egusphere-egu26-9445, 2026.
The multi-layered transboundary Kalahari aquifer system spanning across Namibia, Botwswana, South Africa, and Zimbabwe, comprises the transboundary Stampriet basin (A005, according to the classification of the International Groundwater Resources Assessment Center IGRAC). This aquifer system reaching from the foothills of the Great Escarpment in Namibia south-east into South Africa, forms a complex and partly artesian multi-aquifer system that is used for drinking water supply, irrigation agriculture and is prospected for in situ-leaching mining. In order to establish functional and geochemical baselines for the major large-scale transboundary aquifer, an integrated hydrological, hydrogeological, geochemical and isotopic assessment has been carried out. The system boundaries have been re-assessed to integrate the contributing hydrological basins outside of the aquifer system proper that constitute the dominant source of indirect recharge by transmission losses from ephemeral streams. A coupled surface-groundwater model provided the direct and indirect recharge sources for the Stampriet groundwater model. The study has shown that at a basin scale of about 10.000 km² indirect recharge by transmission losses becomes the predominant recharge mechanism, establishing the importance of analysing this recharge source in large groundwater basins, especially in arid zone groundwater systems. The currently available data on hydrochemical and isotopic groundwater composition have been collected, combined with existing databases from previous projects on the Kalahari/Stampriet basin and re-assessed to derive geochemical baselines. Geochemical baselines have been established for the main aquifer units based on a geochemical groundwater classification. The geochemical analysis has been supported by sampling of trace element and isotopic geochemical indicators for the groundwater evolution in the aquifer system to delineate the development, establishment and stability of geochemical and redox-reaction zones. A re-analysis of residence time tracers has been being carried out to derive and evaluate flow paths and travel times in different aquifers. Based on these data an open source large scale compartment model has been developed to construct groundwater flow patterns based on residence time tracers and geochemical end members. The compartment model calculates the quantitative flow rates between aquifer units based on an a series of hypothetical a priori conceptual models. Closure of hydrological and geochemical mass balances and coherence with available residence time data (tritium, carbon-14) are used to validate the flow model. Results of the study indicate indirect recharge plays a larger role than previously assumed. The unconfined/confined transition zones control recharge and exchange mechanisms and geochemical zonation. The compartment model provides a quantitative assessment of recharge, flow and inter-aquifer exchange rates that is independent from previous numerical groundwater modeling and constitutes, in combination with residence time tracers and geochemical indicators, an additional source of information for the study of complex aquifer systems.
How to cite: Külls, C. and Krüger, N.: Large Scale Compartment Modeling of the Transboundary Kalahari-Stampriet Aquifer System, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21312, https://doi.org/10.5194/egusphere-egu26-21312, 2026.
Groundwater is among the largest freshwater storages on Earth and is a vital source of water for domestic, industrial, and irrigation purposes worldwide. In Africa, domestic water supply in both urban and rural areas largely depends on groundwater, often abstracted from shallow aquifers. Although groundwater is commonly perceived as a clean and safe water source, increasing anthropogenic pressures threaten its quality, potentially leading to negative health, social, and economic outcomes. Despite its importance, groundwater quality remains poorly monitored across much of the continent. Consequently, groundwater vulnerability and pollution risk assessments frequently rely on index-based approaches such as DRASTIC, which integrates hydrogeological factors including depth to the water table, net recharge, aquifer media, soil, topography, vadose zone, and hydraulic conductivity. At continental scales, these assessments depend heavily on global datasets and large-scale model outputs, introducing substantial uncertainty that is rarely quantified.
Here, we present the first pan-African multi-model intercomparison of groundwater vulnerability and pollution risk based on the DRASTIC framework. We analyze an ensemble of 12 groundwater vulnerability maps, generated by combining three depth-to-water-table datasets and four groundwater recharge models, and 48 groundwater pollution risk maps that additionally incorporate four gridded population datasets. Model disagreement is systematically quantified using Fleiss’ extent of agreement, enabling the identification of dominant sources and spatial patterns of uncertainty across Africa.
Our results reveal widespread disagreement among groundwater pollution risk maps across the continent, highlighting the strong sensitivity of continental-scale assessments to key hydrogeological and anthropogenic inputs. Uncertainty in population datasets drives major disagreement hotspots in the Sahel and parts of Central and East Africa, whereas differences among depth-to-water-table datasets dominate uncertainty across arid regions such as the Sahara and Kalahari deserts. Uncertainty in groundwater recharge estimates further contributes to model divergence in several humid and semi-arid regions across the continent. Using the ensemble, we explore compromise mapping approaches that synthesize model outputs to produce more informative and robust groundwater vulnerability and pollution risk maps.
Overall, our findings demonstrate that large-scale groundwater vulnerability and risk maps should be interpreted as uncertainty-informed products rather than deterministic outputs. Explicitly quantifying and communicating uncertainty is essential for improving confidence, transparency, and the responsible use of groundwater vulnerability assessments in data-scarce regions of Africa.
How to cite: Fridman, D., Hinton, R., Nazari, S., Artuso, S., Willaarts, B., and Kahil, T.: Multi-model assessment of uncertainties in continental groundwater vulnerability and pollution risk mapping in Africa, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9357, https://doi.org/10.5194/egusphere-egu26-9357, 2026.
Posters virtual: Tue, 5 May, 14:00–18:00 | vPoster spot A
EGU26-16340 | Posters virtual | VPS8
Propagation of Meteorological Drought to Groundwater Drought in IndiaTue, 05 May, 14:57–15:00 (CEST) vPoster spot A
Groundwater drought poses a growing threat to water security in India, as groundwater supplies support agriculture, ecosystems, and domestic use. Although meteorological and hydrological droughts and their propagation have been studied, the propagation of drought into groundwater systems in India has not been examined. In this study, we employed Standardized Precipitation Index (SPI), the CGWB-based Standardized Groundwater Index (SGI), and the GRACE-based Groundwater Storage Anomaly (GWSA) to investigate meteorological drought and groundwater drought across the Indian region. We estimated drought propagation duration, recovery duration, mean drought duration, and maximum drought duration. The results show that regions in the north, northwest, northeast, and a few regions in southern India have the longest propagation time from meteorological to groundwater drought, while other zones, such as central India, have relatively shorter propagation times. We also find that regions in northeast and northwest India recover faster from groundwater droughts than other regions. Our results also show that the Dryness Index (DI), Seasonality Index (SI), and Land Surface Controls (NDVI, soil moisture (SM), and Evapotranspiration (ET)) play a significant role in the propagation time of meteorological to groundwater droughts across different zones. Overall, understanding the propagation and recovery plays a vital role in aiding effective management and planning of groundwater resources in India.
How to cite: Aayush, A. and Mishra, V.: Propagation of Meteorological Drought to Groundwater Drought in India, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16340, https://doi.org/10.5194/egusphere-egu26-16340, 2026.
