Spatio-Temporal Variations in China’s Groundwater Reservoirs from 2005 to 2024 Based on GRACE Data

Groundwater is a critical component of the terrestrial water system, and understanding the spatiotemporal evolution of national groundwater storage is essential for ensuring water security and ecological sustainability in China. Based on GRACE and GRACE-FO satellite gravity data from January 2005 to December 2024, combined with land surface water components derived from GLDAS, this study investigates the spatiotemporal variations and driving mechanisms of groundwater storage anomalies (GWSAs) across China using parametric additive decomposition, Theil–Sen trend estimation, and the Mann–Kendall significance test. The results indicate that: (1) groundwater storage in China has experienced a persistent decline at an average rate of −1.97 mm yr−1, with a cumulative depletion of 38.55 mm. This decline exhibits distinct phases, characterized by a rapid decrease during 2005–2011, a moderated decline during 2012–2017, and a renewed acceleration with increased variability during 2018–2024; (2) spatially, GWSA shows a pronounced “increase in the south and decrease in the north” pattern, with extremely significant declines concentrated in the North China Plain and arid northwestern inland regions, while significant increases are mainly observed in southwestern China and southeastern coastal areas; (3) GWSA exhibits a stable seasonal cycle of “summer surplus and spring deficit,” with groundwater replenishment driven by summer precipitation and substantial depletion caused by agricultural water demand in spring; and (4) groundwater variations in northern China are primarily controlled by intensive agricultural irrigation, resulting in sustained depletion, whereas southern China is mainly influenced by natural precipitation, maintaining a relatively dynamic equilibrium. These findings provide valuable insights for region-specific groundwater management and the sustainable utilization of water resources in China.