Quantifying terrestrial and groundwater storage depletion in Shaanxi Province, China: insights from multi-source GRACE(-FO) and hydrological data

Amid large-scale ecological restoration, a noteworthy hydrological phenomenon has emerged in Shaanxi Province: while vegetation is significantly greening, both terrestrial water storage (TWS) and groundwater storage (GWS) continue to decline. Employing a multi-product diagnostic framework to analyse five GRACE(−FO) solutions and construct an optimized ensemble, we provide a holistic quantification of water storage depletion across this semi-arid-to-semi-humid transitional zone from 2003 to 2020. Our results reveal a pronounced southwest-to-northeast gradient of water loss. The Loess Plateau (Shanbei) is the most affected, with TWS declining at −9.71 ± 0.66 mm yr−1 and GWS plummeting at −10.93 ± 0.54 mm yr−1, compared to relatively stable conditions in the mountainous south (Shannan). Furthermore, our multi-product intercomparison reveals a systematic divergence in the JPL-M solution over the Qinling – Bashan mountainous terrain, underscoring the need for product-level cross-validation as a prerequisite for robust GRACE-based water budget assessments in topographically complex regions. We attribute this depletion to a double burden: climate warming (+0.45°C (10 yr)−1) is intensifying evaporative demand, but more critically, we mechanistically link the paradox of large-scale vegetation greening (NDVI +0.063 (10 yr)−1 in Shanbei) to water scarcity by demonstrating that enhanced transpiration from restored ecosystems, coupled with direct agricultural and industrial groundwater extraction, is consuming the very resource upon which long-term restoration depends. Our findings uncover a fundamental trade-off for semi-arid zone management: ecological restoration policies must reconcile vegetation recovery with the carrying capacity of finite water resources.