Global Warming Will Increase the Risk of Water Shortage in Northwest China

Drylands with fragile ecosystems and severe water shortages are particularly vulnerable to climatic change. Northwestern China (NWC), a typical arid region, faces uncertainty regarding future wetting or drying trends. A comprehensive assessment and projection of these conditions are crucial for water resource management. In this study, we employ a Lagrangian trajectory model, optimal fingerprint analysis, and a maximum covariance technique to evaluate wetting and/or drying trends in NWC over the historical (1981–2023) and future (2024–2099) periods. Our results show that over 80% of NWC experienced increases in air temperature, precipitation, and evaporation during the historical period. External and internal water vapor sources contribute 92% and 8%, respectively, to precipitation changes. Incoming water vapor predominantly originated from the North Atlantic (31.9%) and the South China Sea ‐ Bay of Bengal region (39.3%), with a strong positive correlation (r = 0.71) between Atlantic sea surface temperatures and precipitation minus evaporation in NWC. Water vapor enters NWC from the southern, northern, and western boundaries, while 83.4% escapes through the eastern boundary. The precipitation trend is strongly influenced by the combined effects of anthropogenic and natural forcings, accounting for 36.8% to the observed increase. Under a 1.5°C warming scenario, warming‐wetting regions shift northward, whereas higher warming levels (2°C, 3°C, 4°C) cause these regions to shift southeastward and shrink. Our findings underscore NWC's high sensitivity to climate warming and highlight the pressing challenge of water security in a warming world.