Associated Summer Rainfall Changes over the Three Rivers Source Region in China with the East Asian Westerly Jet from 1979 to 2015

Under the intensification of global warming, the characteristics of the Three Rivers source region (TRSR; i.e., headwaters of the Yellow River, the Yangtze River, and the Lancang River) in China were diagnosed in the summer season from 1979 to 2015 using observations and reanalysis data. The diagnoses indicate that summer precipitation decreased from 1979 to 2002 [by 9.01 mm day(-1) (10 yr)(-1); p < 0.05 by Student's t test] and increased significantly after 2002 [by 5.52 mm day(-1) (10 yr)(-1)]. This abrupt change year (2002) was further confirmed by the cumulative anomaly method, the moving t-test method, and the Yamamoto method. By compositing the thermodynamics before and after the abrupt change year (2002), the results reveal that increased water vapor and more substantial lower-level convergence were present over the TRSR during 2003-15. This marked interdecadal variability in the TRSR summer precipitation responded to the interdecadal position and intensity of the large-scale forcing East Asian westerly jet (EAWJ), which is significantly modulated by the low-frequency variability associated with Southern Oscillation index. The connection between the interannual TRSR precipitation and the location and intensity of EAWJ was also explored. The position index of the EAWJ is negatively (with correlation coefficient R of -0.446; p < 0.05 by Student's t test) correlated with the precipitation over the TRSR, implying that southward and northward years of EAWJ are respectively associated with intensifying and weakening the TRSR summer precipitation, whereas the intensity of EAWJ is insignificantly correlated with the TRSR summer precipitation.

Automated summary

Under the intensification of global warming, the characteristics of the Three Rivers source region in China were diagnosed using observations and reanalysis data. The study found significant interdecadal variability in summer precipitation in this region, with a noticeable increase after 2002, which was strongly associated with the interdecadal position and intensity of the East Asian westerly jet. The study also revealed a negative correlation between the position index of the East Asian westerly jet and precipitation in the Three Rivers source region.