Spatiotemporal Variations of Terrestrial Water Storage and Driving Factors in the Water Towers of Northwest China Based on GRACE and Multi‐Source Data Sets

Abstract Mountains represent important water towers and thus are the primary water suppliers for downstream areas. However, divergent trends in terrestrial water storage (TWS) in water towers and their driving factors have not been clarified. This study investigated water tower units (WTUs) in Northwest China (NWC) and used GRACE/GRACE‐FO and multi‐source remote sensing data to analyze the spatiotemporal changes in TWS over the past 20 years. Based on correlation analysis and structural equation modeling, the effects of precipitation (PRE), evapotranspiration (ET), temperature (TEM) and NDVI on TWS were revealed. The results showed that TWS decreased in the WTUs of the Junggar and Ili River basins while increasing in the Qaidam and Yellow River basins. Glacier retreat and snowmelt were the components that contributed the most to TWS changes in the WTUs of the Tarim, Junggar, Ili River, and Irtysh River basins, while lake expansion, groundwater, and soil moisture contributed the most in the remaining WTUs. Additionally, the dominant roles of climate and vegetation factors on TWS changes varied significantly among the WTUs. For example, glacial retreat and increased ET caused by climate warming and vegetation greening exacerbated the TWS reductions in WTUs of the Junggar and Ili River basins, whereas vegetation greening dominated TWS changes within the Yellow River basin by affecting groundwater storage and soil moisture. These findings are crucial for understanding changes in the hydrological cycle of water towers and optimizing future watershed water resource management strategies.