Quantitating the Summer Moisture Sources over Northwest of China and Its Annual Variations in Dry and Wet years

Using the Community Atmosphere Model version 5.1 (CAM5.1), in which atmospheric water tracer technology is incorporated, atmospheric moisture (water vapor and precipitation) source regions of summer northwest of China (NWC) are quantitatively identified based on the offline simulations for 1982–2021. Inconsistent to some previous studies, our study revealed that land-supplied moisture directly contributed much larger than ocean-supplied to NWC. For example, the local evaporation from NWC itself accounted for 22.3% of the water vapor over NWC, and from north Asia, Europe, Tibet plateau (TP) and southeast of China (SEC) accounted for 19.6%, 16.0%, 5.0%, 4.5%, respectively. North Indian Ocean (NIO) was the most important source from ocean-supplied to NWC water vapor, while only accounted for 6.0% to water vapor over NWC. Interestingly, the sources of precipitation over NWC were inconsistent to that of water vapor due to the difference of precipitation efficiencies from every source region, which related to weather patterns corresponding to moisture sources. For example, the moisture sources from SEC and TP contributed 9.5% and 8.2% to precipitation over NWC respectively, larger than the contribution ratios of water vapor, due to their higher precipitation efficiencies corresponding to favorable synoptic pattern. While lower precipitation efficiencies corresponded to unfavorable synoptic pattern from Europe and north Asia, contributed to 11.5% and 11.2% to the precipitation over NWC. Also, we will present the long-term trend of summer moisture source regions over NWC, and the annual variations of summer moisture sources in dry and wet years.