Evaluating the spatio-temporal groundwater stress with data-driven models and satellite data for the Ganga River Basin.

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.