Soil Aquifer Treatment (SAT) relies on biogeochemical processes occurring within the vadose zone to improve the quality of secondary treated wastewater during infiltration. Dissolved organic matter (DOM) is a key driver of these processes; however, its depth-dependent transformation within the soil profile remains insufficiently resolved at the molecular level under field conditions.

In this study, we investigated the vertical evolution of fluorescent dissolved organic matter (fDOM) within the soil profile of a full-scale SAT infiltration basin. Soil samples were collected from successive depths along the vadose zone, representing progressive stages of soil–water interaction during infiltration. DOM composition was characterized using excitation–emission matrix (EEM) fluorescence spectroscopy with inner-filter correction and Raman normalization. Fluorescence data were analysed using Coble peak integration and Parallel Factor Analysis (PARAFAC) to resolve independent fluorescent components and assess their depth-dependent behaviour.

The results reveal pronounced vertical stratification of DOM composition within the soil profile. Shallow soil layers are dominated by protein-like fluorescence associated with labile, wastewater-derived organic matter. With increasing depth, these protein-like signals show strong attenuation, while humic-like fluorescence becomes increasingly dominant. Coble peak analysis indicates preferential removal of tryptophan- and tyrosine-like peaks (B and T), whereas humic-like peaks (A, C, and M) persist at depth. PARAFAC modelling further identifies distinct fluorescent components exhibiting contrasting depth trends, with protein-like components rapidly decreasing in intensity and humic-like components remaining relatively stable or proportionally enriched.

These findings demonstrate that SAT acts as a selective biogeochemical filter within the soil profile, where biodegradation and sorption processes preferentially remove reactive DOM fractions in the upper vadose zone while more refractory humic material persists at depth. The combined use of EEM–PARAFAC provides mechanistic insight into DOM transformation pathways during soil aquifer treatment and highlights the importance of depth-resolved fluorescence analysis for improving process-based understanding of SAT performance.

How to cite: Adler‬‏, O.: Vertical transformation of fluorescent dissolved organic matter within the soil profile of a soil aquifer treatment basin, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19818, https://doi.org/10.5194/egusphere-egu26-19818, 2026.

Uranium contamination in shallow aquifers is emerging as a concern for groundwater-quality issues across several parts of India. The present study evaluates the spatial distribution, concentration levels in shallow groundwater systems of selected semi-urban regions of India. Secondary data used in this assessment were obtained from the Central Ground Water Board (CGWB), covering semi-urban areas across all Indian states. The results reveal pronounced spatial heterogeneity in uranium concentrations, with numerous locations exceeding the permissible limits prescribed by the World Health Organization (WHO) and the Bureau of Indian Standards (BIS) for drinking water. Analysis of uranium concentration data for the period 2024–2025 indicates that shallow aquifers in parts of Karnataka, Punjab, and Rajasthan exhibit average uranium concentrations of approximately 133 ppb, 48 ppb, and 79 ppb, respectively, while maximum concentrations of 488 ppb, 202 ppb, and 119 ppb respectively, were recorded at select locations. A substantial proportion of groundwater samples were found to exceed WHO guideline values, highlighting widespread contamination concerns. The findings of this study offer critical insights for water-resource managers and policymakers in developing strategies to protect drinking-water security in uranium-affected regions of India.

How to cite: Kumar, D., Khare, S., and Kurre, S.: Spatial Variability of Uranium in Shallow Aquifers of Semi-Urban Indian Landscapes, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6358, https://doi.org/10.5194/egusphere-egu26-6358, 2026.

Groundwater contamination arising from mining activities represents a persistent and complex environmental challenge, particularly in coal-bearing regions where sulfide-rich mine overburden is extensively exposed to atmospheric conditions. Upon interaction with oxygen and moisture, pyrite oxidation generates acidic by-products and mobilizes dissolved constituents, such as ferrous, ferric iron, sulfate, and hydrogen ions. Understanding and predicting the spatiotemporal evolution of contaminant plumes in such systems remains challenging due to the coupled nature of variably saturated flow, multicomponent geochemical reactions, and microbially mediated processes. This study develops a comprehensive numerical modeling framework for simulating contaminant transport and remediation processes associated with oxidation reactions in unsaturated mine overburden systems. Variably saturated flow is represented through discretization of the governing flow equation in the vertical domain using hydraulic head-based parameters, and the resulting tridiagonal system of linear equations is efficiently solved using the Thomas algorithm. The model couples variably saturated groundwater flow, represented by Richards’ equation, with multicomponent reactive transport equations describing the generation and migration of key oxidation products (Fe²⁺, Fe³⁺, SO₄²⁻, and H⁺). In addition, sulfate reduction mediated by sulfate-reducing bacteria (SRB) is incorporated to capture biologically driven attenuation mechanisms relevant to natural and engineered remediation scenarios. Simulations are performed for a total of 22 years (8030 days). A time step of 0.1 day and a grid size of 0.2 m are identified as the optimal choices for the simulations. The simulation results indicate that the concentrations of oxidation-derived species decrease significantly from 200 to 40 mol/m³ in clay, 300 to 95 mol/m³ in loam, and 1 to 0.2 mol/m³ in sand. Sensitivity analysis shows that peak sulphate sensitivity in clay with a sensitivity index (SI) of 0.65 and in loam with an SI of 0.5 under high saturation condition (water content, w_c = 0.9), while ferrous ions exhibit maximum sensitivity in loam under low saturation condition (w_c = 0.2) with an SI of 750. The findings support the development of predictive frameworks that can inform sustainable groundwater management, optimize remediation strategies, and address key challenges in the practical application of contaminant transport models.

How to cite: Roy, G. and Sivakumar, B.: Hydrogeochemical Forensics of Pyrite Oxidation in Unsaturated Mine Overburden: A Numerical Simulation Framework for Groundwater Contaminant Migration., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12747, https://doi.org/10.5194/egusphere-egu26-12747, 2026.

Groundwater is a critical water resource in Morocco, particularly in semi-arid regions where agricultural demand and local uses place increasing pressure on aquifers. In this setting, a clear and spatially explicit assessment of groundwater quality is essential to support monitoring strategies and contribute to more sustainable water management.

This study presents an approach for characterizing groundwater quality in a semi-arid area of Morocco based on physico-chemical analyses of groundwater samples collected from wells and springs. Water quality is identified through the computation of a groundwater quality index derived from multiple measured parameters, providing a synthetic and comparable metric across sampling points. The results are then integrated within a Geographic Information System (GIS) framework to explore spatial patterns and support interpretation at the territorial scale. Spatial interpolation is used to map the distribution of both the individual parameters and the quality index, highlighting local contrasts and potential hotspots within the study area.

Overall, the findings indicate generally satisfactory groundwater quality, while also revealing localized variations that justify targeted follow-up and site-specific attention. The proposed workflow is transferable and can be adapted to other semi-arid settings in Morocco to support diagnosis, prioritization of actions, and long-term, sustainable groundwater resource management.

How to cite: Mouncif, A., Nait-Taleb, O., Karroum, M., Krimissa, S., Namous, M., and Elaloui, A.: Groundwater quality assessment in semi-arid Morocco: spatial analysis and monitoring, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15319, https://doi.org/10.5194/egusphere-egu26-15319, 2026.

Reliable baseflow estimation plays a crucial role in water resource management across India's monsoon-dominated landscapes, where groundwater contributions sustain river flows through extended dry periods. This study addresses persistent data limitations in Central and Southern India by first compiling daily streamflow records from 4,862 basins sourced from the India Water Resources Information System (IWRIS), followed by rigorous pre-processing and quality control steps that yielded suitable data for analysis across hundreds of representative basins. A comprehensive evaluation of 12 baseflow separation methods was then conducted using Kling-Gupta Efficiency (KGE) against hydrologically verified baseflow benchmarks, revealing digital filter techniques, particularly the Eckhardt filter (median KGE of 0.88) as superior to conventional graphical methods across diverse hydrological regimes. These findings affirm digital filters' reliability for capturing baseflow variability in monsoon recharge areas and arid inland zones, laying a strong foundation for advanced hydrological modeling in data-constrained environments.

Keywords: Baseflow Separation, Digital Methods

How to cite: Samyuktha, P., Dubey, S., and Gautam, S.: Comprehensive Evaluation of Baseflow Separation Methods for Peninsular India, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21596, https://doi.org/10.5194/egusphere-egu26-21596, 2026.

Accurate or exact estimations of hydraulic conductivity (K) and infiltration rate are crucial for understanding soil-water interactions, optimising irrigation practices, evaluating groundwater recharge potential, and designing drainage systems. Conventionally laboratory permeability tests and in-situ infiltrometer tests, provide direct estimates of soil hydraulic behaviour. However, these methods have limitations of their point-specific nature and are unable to capture subsurface heterogeneity across larger spatial scales. In contrast, the electrical resistivity tomography (ERT) technique offers a non-invasive geophysical approach that is capable of detecting subsurface variations in soil electrical resistivity properties. The electrical resistivity estimates can further be interpreted to analyse soil types, soil layer structures, moisture and mineral contents, and pore connectivity. These are ultimately related to soil hydraulic properties, such as hydraulic conductivity and soil-water interaction behaviour, such as vertical infiltration rates. One of the accurate methods of estimating K is a pumping test, which is expensive and time-consuming. Other methods include laboratory permeameter tests, which require the collection of soil samples from the field, which often are disturbed ones and thus may produce K values with considerable uncertainties. The primary goal of this study is to establish the relationship between hydraulic conductivity (K) and electrical resistivity (ER) to replace the tests mentioned above. The second objective of this study is to establish an ER-infiltration rate relationship to convert point-based infiltration measurements into area-wide infiltration maps using resistivity data, minimizing the number of infiltrometer tests needed, saving time, manpower, and resources. Field investigations executed here involve ERT surveys using different electrode configuration arrays, such as the Wenner, Schlumberger, and dipole-dipole, across selected test sites that represent various soil textures and moisture conditions. The resistivity profiles are inverted to generate 2D subsurface sections, enabling identification of moisture zones and shallow saturation patterns. Parallelly, laboratory permeability tests are carried out on undisturbed soil samples to determine hydraulic conductivity, while infiltrometer tests are performed to obtain field-scale infiltration characteristics and steady-state infiltration rates. The combined dataset provided a comparative evaluation of resistivity variations in relation to measured soil-hydraulic parameters. Once these relationships are established, ERT can move beyond the simple imaging and serve as a fast and cost-effective way to estimate how water moves through the soil over a wider area. This will significantly reduce the need for frequent point-based tests and help capture natural variations in soil conditions that are often required in hydrological studies. Site evaluations can thus become faster and efficient, while areas with higher infiltration potential can be identified with greater confidence, and the overall planning of irrigation, drainage, and groundwater recharge strategies becomes more informed and robust.

Keywords: Electrical Resistivity Tomography (ERT); Hydro-geophysical characterization; Hydraulic Conductivity; Infiltration Rate; Groundwater recharge; Soil Heterogeneity.

How to cite: Jaiswal, M., Ganguly, S., and Prashanth, T.: Integration of electrical resistivity tomography, permeability and infiltrometer tests for modelling hydraulic conductivity and infiltration rates in the field, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3766, https://doi.org/10.5194/egusphere-egu26-3766, 2026.

Quarry lakes, primarily located in alluvial plains, form as a result of the deepening of quarry excavations beyond the water table of the shallow aquifer.

They allow for full exploitation of the deposit without excessively damaging the landscape, limiting land consumption. Quarry lakes play also an important ecological and landscape role, because they provide (i) habitats for aquatic plants, aquatic animal species and birds, and (ii) recreational opportunities. Additionally, they contribute to management of water resources and mitigation of flood risks.

In the Piedmont region (NW Italy), quarry lakes are numerous and of considerable size due to the high market demand for concrete and aggregates. These quarry lakes are mostly located along the Po River, the main river of the region, and its main tributaries.

This study focused on six active quarry lakes and, primarily, a hydrogeological reconstruction of the surrounding areas was carried out. Lake water samples were collected in the summer and autumn of 2025 and analysed for hydrochemical composition. Field parameters, including pH, electrical conductivity, and water temperature, were also recorded.

The hydrochemical results, compared with data from the regional network of groundwater monitoring wells, reveal a strong correlation between lake waters, the surface aquifer, and watercourses. The chemical characterization of these quarry lakes supports the study of their  photochemical activity, and the assessment of their potential use as nature-based basins for quaternary treatment of water, thus allowing to minimize the overexploitation of groundwater resources in a context of more frequent drought events due to climate change.

How to cite: Pigozzi, G., Bianco Prevot, A., Biasio, L., Carena, L., Cocca, D., De Luca, D. A., Egidio, E., Lasagna, M., and Mittaridonna, A.: Hydrogeological and Hydrochemical Characterization of Quarry Lakes in the Piedmont Alluvial Plain, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13428, https://doi.org/10.5194/egusphere-egu26-13428, 2026.

Urban and peri-urban regions in semi-arid India are increasingly exposed to contrasting climatic extremes, namely water scarcity and flooding, driven by complex interactions between anthropogenic pressures and biophysical processes. In this context, the present study investigates long-term changes in the annual water yield (AWY) ecosystem service across sub-watersheds of the Godavari River Basin encompassing the semi-arid Warangal district, Telangana, India. The InVEST AWY model is applied for two representative years, 1995 and 2025. The results indicate that AWY ranges from 460-890 mm yr⁻¹ in 1995, with relatively higher values in the north-eastern sub-watersheds, but declines across most sub-watersheds by 2025 to 220-690 mm yr⁻¹. The annual precipitation found to be 1400 to 1230 mm yr⁻¹ over the study period, while potential evapotranspiration increase substantially from 2253 to 2955 mm yr⁻¹, enhancing atmospheric evaporative demand and reducing water availability. Sensitivity analysis (expressed in terms of elasticity, E), shows that AWY is highly sensitive to precipitation variability (E = 1.84) and moderately negatively sensitive to urban-related biophysical parameters (root restricting depth: E = -0.42, crop coefficient (K_c): E = -0.39).  In contrast, sensitivity to potential evapotranspiration is lower (E = -0.36), highlighting the combined influence of climatic forcing and urban expansion. Spatially, urban land use in 1995 is concentrated in the central region, with cropland and forest dominating the western and eastern parts, respectively, yielding a mean AWY of 718.51 mm yr⁻¹. By 2025, relatively higher AWY zones shift toward the north-eastern region, reflecting reduced evapotranspiration associated with urban expansion; however, the overall mean AWY declines to 476.36 mm yr⁻¹, indicating that land-use changes influenced spatial patterns while climatic factors governed the temporal decline. The decline in AWY between 1995 and 2025 corresponds with reduced ecosystem service values (ESV) for water-yield related regulation services, particularly water regulation (ESV₁₉₉₅ = 16.37 to ESV₂₀₂₅ = 12.91 million US$) and water supply (ESV₁₉₉₅ = 84.73 to ESV₂₀₂₅ = 73.69 million US$). Overall, the findings demonstrate the joint role of climate variability and urbanization in shaping sub-watershed water yield and associated ecosystem services, providing insights for climate-responsive urban and landscape management.

How to cite: Dasari, S., Pal, M., and Keesara, V. R.: Ecohydrological Modelling of Annual Water Yield and Water-Related Ecosystem Services in the Semi-Arid Region of Warangal, India, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9012, https://doi.org/10.5194/egusphere-egu26-9012, 2026.

Sub-daily extreme rainfall (SDER) events frequently lead to natural disasters, including flash floods, urban floods, landslides, and soil erosion. It is essential to make a reliable prediction of its frequency at the local/regional spatial scale for the future period, in order to devise improved disaster mitigation and adaptation strategies. It has been observed that current CMIP6 GCMs have limitations in simulating short-duration (sub-daily) heavy rainfall events, and large biases are often observed in the control run simulations compared to historical observations at various locations worldwide. Hence, there is a lack of confidence in considering the crucial future projections obtained from those GCMs as reliable. In this study, we present a novel statistical methodology for predicting the seasonal frequency of SDER for 99 river sub-basins (RSBs) in India, encompassing tropical, temperate, arid, and polar climates across various topographies. The methodology identifies the scaling relationship between the SDER frequency and the associated potential atmospheric variables/drivers for each RSB. Results indicated that the seasonal frequency of SDER scales with (i) near-surface air temperature (SAT), and (ii) moisture content in the air, which is measured by near-surface dew-point temperature (DPT). The scaling relationship exhibits an increasing (scaling) phase followed by a decreasing (reverse scaling) phase as the (dew point) temperature increases. The range of SAT and DPT in the scaling relationship varies with RSB and climate. The SAT and DPT values at peak frequency are high for mountainous areas and lower for non-mountainous areas. The effectiveness of those scaling relationships in predicting SDER frequency at the seasonal scale was assessed/validated for the recent past (1981-2020). The method performed fairly well for RSBs with non-mountainous topography and moderately well for RSBs with mountainous topography across climate zones, except for years with an abnormally high or low SDER frequency. A finer spatial-resolution scaling relationship is deemed necessary for mountainous topographies where SDER exhibits a rather local nature. In addition, the time trends in simulated and observed frequencies closely matched. The proposed methodology is applied to predict the future seasonal frequency of SDER in the RSBs for different SSP climate scenarios till the end of the twenty-first century. The performance of various GCMs in projecting the seasonal frequency of SDER is also evaluated.

How to cite: Varshney, A. and Srinivas, V. V.: A Statistical Methodology for Regional Scale Future Projection of the Seasonal Frequency of Sub-daily Extreme Rainfall Events, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1058, https://doi.org/10.5194/egusphere-egu26-1058, 2026.

Water resources worldwide are increasingly threatened by growing anthropogenic pressures and inherent hydrogeological constraints, raising concerns about their suitability for domestic use. This study aims to assess the physicochemical quality of certain springs in the Agadir Ida-Ou-Tanane region and evaluate compliance with international thresholds established by the World Health Organization (WHO) for drinking water. A total of twenty-six water samples were collected across the studied region and analyzed for key parameters including Electrical Conductivity (EC), Total Dissolved Solids (TDS) and Total Hardness (TH). The EC values ranged from 275 µS/cm to 4210 µS/cm with an average of 1446.15 µS/cm. For Total dissolved solids, values ranged from 135 ppm to 7140 ppm, with Total hardness presented a maximum value of 3217.02 mg/L and minimum value of 188.9 mg/L. Water Quality Index (WQI) was calculated to provide an integrated evaluation of the overall water quality.Spatial distribution of water quality was further examined through Inverse Distance Weighting (IDW) interpolation. WQI based classification  revealed that 73.1% of the springs were in acceptable quality categories, with 34.6% classified as excellent and 38.5% as good. Despite this generally favorable status, TDS values approach or exceed international thresholds in several locations, indicating the need for region-wide monitoring and treatment strategies. Considering the heavy dependence of rural communities on spring water, these findings underscore the importance of investing in adequate treatment infrastructure and implementing robust protection measures for sustainable water resource management.

How to cite: Raïs, A., Tairi, A., El Mouden, A., Ijlil, S., Ait Moh, H., Hssaisoune, M., and Bouchaou, L.: Geo-statistical and hydrochemical assessment of spring water quality and water sustainability based on WHO standards in the Agadir Ida-Ou-Tanane region, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-873, https://doi.org/10.5194/egusphere-egu26-873, 2026.

Riverbank filtration (RBF) is a managed aquifer recharge (MAR) technique applied worldwide, operating at the river–groundwater interface and offering the potential to enhance both groundwater quantity and quality, thereby improving drinking water supply security. However, its sustainable implementation requires a robust understanding of hydraulic interactions between surface water and groundwater as well as hydrochemical processes, supported by targeted local and regional monitoring strategies. Moreover, recharge efficiency and water quality benefits may vary in response to seasonal and event-based fluctuations in river flow, upstream contaminant inputs, and site-specific aquifer heterogeneity. In our study, we investigated river water–groundwater mixing, along with bank filtrate residence times, to improve the understanding of recharge dynamics at the Kępa Bogumiłowicka RBF site, a key regional water supply system located near Tarnów, southern Poland. Environmental tracers, including stable water isotopes, chloride concentration, water temperature and specific electrical conductance, were combined with high-resolution hydrological, meteorological and groundwater abstraction records. The results demonstrate that RBF is the dominant aquifer recharge mechanism, contributing more than 90% of the year-round yield from seven production wells located near the riverbank. Based on this case study, we propose a practical and transferable framework for efficient RBF monitoring and management. The approach integrates multi-tracer observations with ensemble end-member mixing analysis (EEMMA), combining discrete sampling with continuous physicochemical and hydrometeorological monitoring over at least one hydrological year. This cost-effective workflow enables robust recharge-source assessment, supports the evaluation of both quantitative and qualitative groundwater status, and facilitates proactive responses to upstream pollution events and rapid hydrological changes. As such, it provides a valuable template for the long-term, sustainable and resilient management of MAR-based drinking water resources in shallow alluvial aquifers.

How to cite: Janik, K., Rein, A., and Sitek, S.: sMARt riverbank filtration monitoring: how environmental tracers and high-resolution data support resilient drinking water supply, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3097, https://doi.org/10.5194/egusphere-egu26-3097, 2026.

In various parts of arid and semi-arid region of India such as Rajasthan people are mainly depended on groundwater for fulfil their daily demands like drinking and watering their crops. However, in the Khetri mining region of Jhunjhunu district, extensive mining and smelting of copper and associated sulfide minerals have led to heavy metal contamination and a deterioration in groundwater quality. Therefore, this study evaluates the overall groundwater quality and the related human health risks in the region severely affected by copper mining and metallurgical activities. We have collected total 59 groundwater samples from both pre- and post-monsoon periods and were examined for physicochemical parameters, cations, anions, and heavy metals (Pb, Cd, Cr, Cu, Fe). Multivariate analysis, including PCA and correlation, revealed that geogenic processes, such as carbonate and silicate weathering, dominate natural groundwater chemistry. Whereas anthropogenic inputs from mining, ore processing, agriculture, and industrial waste significantly elevate toxic metal concentrations. The elevated level of Pb, Cd and Cr were detected across many locations, often exceeding permissible limits. Non-carcinogenic risks (HI) for Cr, Pb and Cd surpassed the safe thresholds in many locations, and carcinogenic risks (CR) for Cr, Cd, and Pb exceeds the permitted limit of 1 × 10⁻⁴ at multiple sites, indicating significant long-term health threats. The integrated EWQI–Monte Carlo framework thus combines the objectivity of entropy-based weighting with the statistical power of probabilistic simulation, enabling a more realistic and comprehensive evaluation of both groundwater quality and the related human health risks. In addition of this, the risk assessment for human health (HRA) revealed that children are at more danger than adults due to their greater exposure per body weight. These findings clearly indicate an urgent need for groundwater quality management through the adoption of remediation actions and the exploration of alternative sources to protect community health from contaminated groundwater.

How to cite: Kumar, M., Pathania, T., and Gaurav, K.: Integrated EWQI–Monte Carlo framework for assessing groundwater quality and health risk in the Khetri mining region of Jhunjhunu district, Rajasthan, India, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1227, https://doi.org/10.5194/egusphere-egu26-1227, 2026.

Rapid groundwater depletion, driven by intensive pumping and growing climate variability, poses a critical threat to water security across India. Concurrently, climate change is intensifying the frequency and magnitude of flood events, generating episodic but potentially significant opportunities for natural aquifer replenishment. However, the contribution of floods to groundwater in India remains poorly quantified. In this study, we systematically quantify flood‐driven groundwater recharge across the major river basins of India. Using the integrated, physically based ParFlow-CLM hydrological model, we evaluate three fundamental attributes of flood recharge: (i) the contribution of flood runoff to total groundwater recharge, (ii) the temporal lag between flood peaks and aquifer response, and (iii) the persistence of flood‐induced recharge signals following an event. These metrics are evaluated across diverse hydrogeological settings to identify where floodwaters are most effectively captured and retained within aquifers. Our results show strong spatial contrasts in flood recharge efficiency. The highly permeable alluvial aquifers of the Indus, Ganga and Brahmaputra basins exhibit the highest flood-to-recharge contribution and the longest persistence, indicating a strong capacity to capture and retain floodwater. In contrast, less permeable and fractured hard-rock aquifers in large parts of central and southern India show weaker and shorter-lived recharge responses to floods. By explicitly linking flood dynamics to subsurface hydrologic response, this study provides a framework for identifying priority regions for flood‐based groundwater management. The results demonstrate how increasing flood extremes under climate change can be strategically harnessed to enhance the resilience of India’s groundwater resources.

How to cite: Roy, R. and Mishra, V.: Flood-Driven Groundwater Recharge for India , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16236, https://doi.org/10.5194/egusphere-egu26-16236, 2026.

The global demand for groundwater is expected to increase due to changing hydrological and population patterns. Hence, spatio-temporal characterization of groundwater is crucial for its sustainable management options. This study introduces a fully distributed groundwater simulation model, based on the MODFLOW framework, to understand the fluctuations in the groundwater table and basin-scale hydrological dynamics of the Damodar River basin (DRB) in India. Monthly simulations were conducted over a 5-year period (2015–2020) to quantify changes in groundwater head and interactions between the river aquifer and the watershed. Real field abstraction data were used to represent pumping components of water use in the MODFLOW model. Parameter Estimation Test (PEST) based calibration and validation were performed to estimate the unknown hydraulic conductivity and recharge. The model outcomes reasonably align with heads at the observation wells, thereby improving our understanding of the water table in large river basins. The findings highlight the influence of monsoon precipitation and the overall changes observed in DRB. Furthermore, the study combined the tributary stream network and PEST-calibrated recharge, which further enhanced the physical representation and accuracy of the model despite the additional data requirements. Decline in groundwater level was observed, which potentially highlights unsustainable water management practices in the river basin. The results underscore the significance of numerical groundwater models, which are crucial for informed decision-making in robust groundwater planning interventions.

Keywords: Groundwater, MODFLOW, PEST, recharge, river basin

How to cite: Kumari, A. and Pathania, T.: Assessing spatio-temporal variations of groundwater level in the Damodar River basin, India using MODFLOW, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5224, https://doi.org/10.5194/egusphere-egu26-5224, 2026.

Understanding seasonal water uptake depth (WUD) in trees is critical for assessing trees’ physiological responses to seasonal variability in microclimatic conditions and soil water availability. While broadleaf and conifer species in the Northern Hemisphere have been widely studied, studies of seasonal changes in WUD of large and long-lived evergreen conifers in the Southern Hemisphere are rare.

We investigated the effect of season and tree size on the water uptake pattern of Agathis australis (kauri), a large and long-lived endemic conifer, over an 18-month period. Our study site, a remnant kauri-dominated forest, is located in West Auckland, northern New Zealand. We collected stem cores from seven kauri trees (n = 3 < 50 cm diameter, n = 4 > 100 cm diameter) and soil samples underneath each of the seven trees (organic layer (OL), 0-10 cm, 10-20 cm, 20-30 cm, 30-50 cm, 50-70 cm, 70+ cm) across six seasons (austral spring 23,  austral summer 23-24, austral autumn 24, austral winter 24, austral spring 24, and austral summer 24-25). Water from soil and stem cores was extracted using cryogenic vacuum extraction. We measured δ²H and δ¹⁸O in all samples and used a Bayesian mixing model (MixSIAR) to determine WUD.

Our preliminary results show that across season and tree size, kauri obtained a larger proportion of water from the shallow layer (OL to 30 cm depth; ~ 60%) compared to ~ 40% sourced from layers below 30 cm. There was greater reliance on water from the shallow layer (up to 75%) during austral summer 23-24 and 24-25. We did not observe strong differences in WUD between small and large trees across our study seasons. These insights advance ecohydrological research on Southern Hemisphere evergreen conifers and highlight the importance of understanding species-specific response to microclimatic conditions and changing water availability.

How to cite: Boseren, M., Schwendenmann, L., and Boswijk, G.: Seasonal water uptake pattern in Agathis australis (kauri), a large and long-lived Southern Hemisphere conifer, using water stable isotopes , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8525, https://doi.org/10.5194/egusphere-egu26-8525, 2026.

The Doongmabulla Springs Complex (DSC) is a cluster of groundwater-dependent wetlands located in central Queensland, Australia. The DSC has over 160 individual springs ranging from over 9 ha, with pools of water, down to vents less than 10 cm across, supporting individual grasses. The springs are home to a variety of plant species (many endemic) that are adapted to the unique physico-chemical parameters of the groundwater discharge on which they rely. Wetlands and scalds of the DSC support a listed Threatened Ecological Community of species dependent on this natural discharge of groundwater from underlying artesian aquifers of the Galilee Basin. The springs are protected under Australia’s State and Commonwealth Environmental legislation. 

Aquifer depressurisation due to mine dewatering occurring to the east of the springs has the potential to threaten spring biodiversity in future by reducing groundwater discharge and consequent wetland persistence. Assessing the likelihood and possible magnitude of these threats requires a multi-disciplinary modelling approach to address complex groundwater – surface water – ecosystem interactions: 1) define groundwater pressure change probabilities; 2) simulate likely wetland response; and 3) evaluate potential ecological impacts. Once such a modelling chain is in place, impact mitigation may be assessed, considering the effect of interventions at each stage of the chain.

To support the numerical modelling, extensive hydrological, ecological and physio-chemical data collection and analysis was undertaken to understand spring wetland area and species microhabitats and distributions over multiple scales and time frames, including seasonal and inter-annual variability. Generation of realistic and defensible conceptualisations for the springs is critical and is described in a companion paper (Cresswell, et al., these proceedings).

Regional numerical groundwater modelling (MODFLOW) generated potential groundwater pressure change responses relevant to the DSC source aquifers. Potential groundwater depressurisation over time at the individual spring locations was utilised in a wetland water balance model (GoldSim) to describe wetland persistence, size and seasonality. Water balance outputs were translated into spatial representations of predicted spring hydrology (TUFLOW), generating area and shape configurations that could be compared to historical wetland persistence data and then utilised to predict potential effects on suitable habitat for key flora species under a range of scenarios including mining-related groundwater drawdown and climate change using maximum entropy species distribution modelling (MaxEnt). This latter process relates known species’ occurrences to measurable variables that describe the environment (such as soil moisture, soil salinity and pH) to predict the presence or absence of a species at unsampled locations and under future groundwater drawdown scenarios. 

The results of the application of this novel chain of models have informed a revised impact assessment for the potential impacts of mine dewatering on the unique vegetation communities at the Doongmabulla Springs Complex and enables development of targeted mitigation approaches for individual wetlands and species.

How to cite: Gibson, A., Cresswell, R., Muller, J., Capon, S., Grieger, R., Lloyd, P., Stanton, D., and Yeates, M.: Using a novel chain of models to mimic source aquifer depressurisation  impacts across the Doongmabulla Springs Complex , Queensland, Australia, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8457, https://doi.org/10.5194/egusphere-egu26-8457, 2026.

Extreme precipitation events (EPEs) are expected to increase in frequency and intensity under global warming and can trigger various impacts such as floods and landslides, which can undermine the socio-economic stability by raising the risk of loss of human lives, infrastructure failure and agricultural losses. Consequently, the study of hydroclimatic extremes has grown substantially in the recent decades, supported by high-resolution data and multivariate event-based analytical frameworks that improve understanding and resilience to climate-related risks. The rainfall induced impacts often show a compound nature because the underlying processes are scale-dependent and can overlap and intensify each another. Therefore it is important to consider extremeness across spatio-temporal scales when assessing EPEs. However, the the complex topography and diverse climatic conditions in the Indian Peninsular region pose a key challenge in assessing and characterizing the EPEs. In this context, a comprehensive ranked catalog of EPEs is developed from the 73 year long data set, based on their extremity across spatio-temporal scales. To increase the robustness of the underlying statistical analysis and to make an optimal use of the data, a combination of the peak-over-threshold (POT) method and the cross-scale weather extremity index (xWEI) is introduced to quantify the spatiotemporal extremity. In addition, the study exemplifies the applicability of POT method and compares the resulting extremeness with the conventional annual maxima approach. The catalog identifies EPEs that are jointly extreme across spatial and temporal scales and distinguishes short-lived localized storms from persistent, widespread events, thereby enabling a systematic characterization of EPE typologies. By linking each EPEs xWEI value to the season and meteorological divisions, the catalog offers a consistent basis for comparing historical events, and advances process-based understanding of regional hazard regimes. In summary, the resulting catalog can be a valuable tool in improving the robustness of quantitative risk assessments and enhancing the reliability of climate change attribution analyses.

How to cite: Ganapathiraju, S. A., Voit, P., Marwan, N., and Rathinasamy, M.: Ranked Multiscale Catalog of Precipitation Extremes using Cross Scale Extremity for the Indian Peninsular Region, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10790, https://doi.org/10.5194/egusphere-egu26-10790, 2026.