Abstract: Henan province is one of the regions in China with relatively severe water scarcity. The excessive consumption of groundwater has become an important factor restricting the economic and social development and ecological environment protection in the region. Based on GRACE, GRACE-FO satellite gravity data, and GLDAS land surface assimilation data from 2003 to 2022, this study analyzes the temporal and spatial changes of groundwater reserves in Henan province over the past 20 years using singular spectrum interpolation and time series decomposition methods, as well as the influencing factors. The results show that the variation of groundwater reserves in Henan province over the past 20 years shows a V-shaped trend, with the rate of change decreasing stepwise from the southwest to the northeast. The rate of change before and after 2015 is -15.53 and 8.88mm/a, respectively, and the groundwater in the northeastern region has shifted from deficit to surplus. A comparison of the inversion results with precipitation and water transfer data from the south-to-north water transfer project reveals that precipitation is closely related to the change in groundwater, but it is not the main reason for the long-term decline in groundwater. The replacement of groundwater pumping by deploying surface water for production and living in the receiving area through the south-to-north water transfer project effectively alleviates the groundwater deficit, playing a crucial role in groundwater recovery. The study results provide an important reference for understanding the spatial and temporal changes of groundwater reserves in Henan province over the past 20 years and for better leveraging the role of the south-to-north water transfer project in water management.

Key words: GRACE, GLDAS, Henan province, groundwater storage