Two decades of terrestrial water storage change in the Northern China Farming-Pastoral Ecotone (2002–2024): Components and drivers

Study region: Northern China Farming-Pastoral Ecotone (NCFPE), China Study focus: NCFPE is a climate-sensitive transition zone where water scarcity constrains sustainable development. However, the spatiotemporal evolution of terrestrial water storage (TWS) anomalies and their components, particularly surface water storage (SWS) anomalies, remains poorly understood, limiting reliable driver attribution. We integrate GRACE/GRACE-FO gravimetry, GLDAS simulations, and lake and reservoir datasets (GloLakes and GLWS) to quantify TWS component anomalies during 2002–2024. Multi-source meteorological data and NDVI are combined with GeoDetector and grid-scale correlation analyses to identify dominant climatic and ecological controls. New hydrogeological insights for the region: TWS exhibits pronounced meridional contrasts, with increases in the northeast and southwest but persistent declines across central and southern regions, while widespread SWS gains partially offset subsurface depletion. NDVI-related dominant areas account for nearly 40% of the total area, representing about two-thirds of the effective area. Mechanisms vary spatially: precipitation compensates vegetation water use in the Songliao Basin; ecological restoration and rising demand intensified TWS losses in the Beijing-Tianjin-Hebei region before partial recovery linked to the South-to-North Water Diversion Project; and vegetation growth combined with warming drives sustained depletion on the Loess Plateau. These findings demonstrate how ecological restoration and human interventions have reshaped regional water storage dynamics and emphasize incorporating SWS into TWS assessments for sustainable water management.