Projection of snowfall and precipitation phase changes over the Northwest China based on CMIP6 multimodels

•The rainfall/snowfall is separated by a comprehensive parameterized rain-snow separation model based on China Meteorological Forcing Dataset (CMFD).•The precipitation phase simulated by INM-CM4-8, EC-Earth3, EC-Earth3-Veg, INM-CM5-0, and Earth3-Veg-LR are most applicable among 21 CMIP6 models in Northwest China.•A comprehensive investigation of snowfall and Snowfall to Precipitation Ratio (SPR) changes in future is conducted at multi-spatiotemporal scales of Northwest China.•The biases of snowfall and SPR are correlated with biases of temperature and precipitation simulated by CMIP6 models.•Projection of changes in snowfall and SPR are significantly important for making adaptive strategies of water scarcity in arid region of China. The change of precipitation phase could have profound influence on water cycle and ecological environment in Northwest China (NWC). It has been observed that snowfall is inclined to transition into rainfall under climate warming. However, the evolution process of precipitation phase in the future over the NWC remains poorly understanding. In this study, the performance of snowfall simulated by Coupled Model Intercomparison Project Phase 6 (CMIP6) is evaluated by results of observation-based rain/snow separation, subsequently analyzing the changes in snowfall and precipitation phase under different climate scenarios over the NWC. The results indicated that most of CMIP6 models overestimate snowfall while underestimate the Snowfall to Precipitation Ratio (SPR) over the NWC. The performance of CMIP6 models is poorer in high-altitude mountainous region but relatively more robust in low-altitude areas. Superior performance of five models are selected for analysing changes of snowfall and precipitation phase in the future. Under the SSP1-2.6 scenario, the trend of changes in snowfall is not obviously in the future. Conversely, snowfall is projected to decline at rates of −1.04 mm·10a-1 and −2.94 mm·10a-1 under the SSP2-4.5 and SSP5-8.5 scenarios, respectively, with significant declines in high-altitude zones. The SPR will decrease at rates of −0.19 %·10a-1, −0.64 %·10a-1, and −1.50 %·10a-1 under SSP1-2.6, SSP2-4.5, and SSP5-8.5 scenario, respectively. The magnitudes in changes of snowfall and SPR show significant differences across sub-regions in the future, with low-altitude areas exhibiting upward trends in snowfall and SPR under certain conditions. Winter snowfall in the future shows an increased trend, while declines are observed