Groundwater Storage Dynamics and Attribution in the Wei River Basin Based on Dynamic Downscaling

Intensive groundwater exploitation in the Wei River Basin (WRB) has caused severe depletion. While Gravity Recovery and Climate Experiment (GRACE) satellites monitor these changes, their coarse resolution fails to account for soil erosion-induced mass loss on the Loess Plateau limit basin-scale accuracy. To address this, we developed the groundwater storage model to dynamically downscale GRACE data to the resolution of 0.05° grid. This physically based model integrates Darcy’s law, water-balance principles, and an innovative correction for soil erosion mass migration. Validated against well data with maximum correlative coefficient of 0.73, the model reveals a severe groundwater decline of 55.89 × 108 m3/year from 2003 to 2023. The high-resolution results successfully capture localized over-extraction hotspots in the Guanzhong Plain, showing a west-to-east decreasing gradient in groundwater storage along the Wei River channel. Furthermore, quantitative analysis indicates that human activities, including primarily agricultural and urban extraction, are the overwhelming drivers, accounting for over 80% of storage depletion. This framework provides a robust methodological reference for isolating groundwater signals in erosion-prone regions and supports refined water management in semi-arid basins.