Spatial and Temporal Distribution of Water Storage Changes in Arid Regions of Northwest China under Climate Change

The northwestern arid regions of China (NARC) is widely confronted with severe water scarcity, and climate change has further intensified the regional imbalance between water supply and demand. To improve the management and utilization of limited water resources in NARC, it is essential to investigate the spatial distribution and temporal variability of water resources. In this study, we used a distributed hydrological model (CWatM) to examine spatiotemporal changes in terrestrial water storage (TWS), surface water area (SWA), and groundwater storage (GWS) over 1979-2023, and to identify the key drivers of storage variations. The results show that: (1) Based on the surface water areas of major lakes, reservoirs, and rivers in the arid region of Northwest China, SWA exhibited an increasing trend during the study period (32.1 km² yr^-1), mainly attributable to increased precipitation and glacier melt. In contrast, TWS and GWS decreased at mean rates of 1.21 and 1.05 mm yr^-1, respectively, primarily associated with cropland expansion and rising water withdrawals. (2) From 1979 to 2023, SWA declined in the northern subregion (−0.72 km² yr^-1) but increased in the southern sub-region (51.14 km² yr^-1); this contrast is explained by differences in regional precipitation and temperature changes. Over the same period, TWS decreased by 0.14 mm yr^-1 in northern NWC and by 1.94 mm yr^-1 in southern NARC, while GWS declined by 0.55 mm yr⁻¹ in northern NARC and by 1.72 mm yr^-1 in southern NARC. These north-south disparities are likely related to higher evapotranspiration and greater irrigation water use in southern NARC compared with the north. Overall, these findings are critical for improving our understanding of hydrological-cycle changes in NARC and for informing future watershed-scale water resources management strategies.