Quantifying Groundwater Storage Loss in The Northwestern Indo-Gangetic Alluvial Plain Using Integrated Geodetic Measurements and Geophysical Modelling

The rapid human-driven depletion of groundwater resources across the Indian subcontinent poses a critical threat to long-term water and food security. The Northwestern Indo-Gangetic Alluvial Plain (NIGAP) is experiencing persistent groundwater depletion due to the combined effects of intensive agricultural and industrial demands. This region, situated on the seismically active Himalayan Foreland Basin, relies heavily on its vast Quaternary alluvial aquifer system. In this study, we integrate multiple geodetic approaches to quantify the secular mass loss in this water-stressed region and partition it into changes in total water and groundwater storage (TWS and GWS).

We analyze time series of TWS changes observed at 300-400 km spatial resolution by the Gravity Recovery and Climate Experiment (GRACE/GRACE-FO) missions from 2002 to 2024. These basin-scale mass estimates are compared with hydrological mass change signals inferred from high-resolution vertical land motion (VLM) derived from Interferometric Synthetic Aperture Radar (InSAR), complemented by continuous Global Positioning System (GPS) measurements. The vertical deformation field derived from InSAR and GPS data across NIGAP reveals aquifer compaction driven by pore pressure decline, enabling the quantification of GWS loss through poroelastic compaction models. However, regions outside the aquifer system exhibit elastic uplift of the Earth’s crust in response to reductions in TWS at and beneath the surface. To convert this elastic response into an equivalent TWS change, we implement an inverse elastic half-space model that incorporates observed surface deformation, along with the known elastic and hydrogeological properties of the study area.

Keywords: Groundwater Depletion, Geodetic Measurements, Elastic Half-Space, Indo-Gangetic Plain.