Using the observational data and simulation results from the Coupled Model Intercomparison Project Phase 6 (CMIP6), precipitation changes in Northwest China during 1979-2019 and under future global warming conditions are studied. Observations show that annual mean precipitation increased significantly in the arid and semi-arid areas of Northwest China over 1979-2019. Precipitation increased significantly in all seasons, with the largest increase in autumn. CMIP6 projection simulations show that precipitation in Northwest China will continue to increase from 2015 to 2100 along with global warming. Compared with that of the other regions in China, the increase of precipitation percentage is the largest in Northwest China. According to the projection of multi-mode ensemble mean, under the SSP2-4.5 and SSP5-8.5 scenarios, the increasing rates of annual mean precipitation in Northwest China are about 1.6%/(10 a) and 3.0%/(10 a), respectively. By the end of the 21st century, the annual mean precipitation in Northwest China will increase by ~13.7% (37 mm) for SSP2-4.5 and ~25.8% (78 mm) for SSP5-8.5. The seasons with the largest increase in precipitation are summer for SSP2-4.5 and spring for SSP5-8.5. Considering that evaporation in Northwest China will also increase with global warming, the annual mean net precipitation in Northwest China will increase by ~1.4% for SSP2-4.5 and ~4.9% for SSP5-8.5 at the end of the 21st century. Consequently, the increase of near surface soil moisture in Northwest China are ~10% for SSP2-4.5 and ~20% for SSP5-8.5. These results indicate that there is a significant wetting trend in Northwest China in the future. Further analysis also shows that future precipitation increasing in Northwest China are due to decreases of geopotential heights at the lower troposphere, which enhances upward motions.

Keywords： Wetting in Northwest China; Precipitation; Global warming; Soil moisture; Future projection