Comprehensive understanding of hydrological drought based on GRACE data at multiple spatiotemporal scales in Northwest China

The gravity recovery and climate experiment (GRACE) satellites offer significant advantages for monitoring changes in terrestrial water storage (TWS), and the data are widely used in hydrological drought research. This study analysed TWS variations from 2003 to 2022 in Northwest China (NWC) at different spatiotemporal scales. We utilized the water storage deficit and water storage deficit index to identify hydrological drought events and explore the spatiotemporal evolution of drought severity. The results indicated that (1) there was a declining trend (− 1.75 mm/a, p < 0.05) in TWS in NWC. Subregional analysis revealed an increasing trend in the Qilian Mts and the Plateau of Qinghai, and the most significant TWS loss was observed in the Tianshan Mts (− 18.07 mm/a, p < 0.05). (2) During the study period, a total of seven drought events were observed in NWC. The eastern part of Lanzhou, which was prone to drought, had the highest frequency of drought (15 events). (3) An abrupt change in TWS occurred in 2012, after which the drought occurrence shifted from the southern region to the northern region. The drought severity in the Tarim River Basin, the Hexi Inland River Basins, the eastern part of Lanzhou, the Tianshan Mts, and the Altai Mts tended to increase, whereas that in the Qilian Mts and the Plateau of Qinghai tended to decrease. Glacial retreat, increased snowfall, and permafrost thaw are considered critical factors for drought in mountainous areas. These results provide a spatiotemporal perspective on regional water resource changes, which contributes to the development of water transfer strategies for drought hazards.