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

Abstract Under the intensification of global warming, the characteristics of the Three Rivers Source Region (i.e., headwaters of the Yellow River, the Yangtze River, and the Lancang River, TRSR) 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 1979-2002 (9.01 mm/day /10a, p<0.05 by student’s t-test) and increased significantly after 2002 (5.52/10a). 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 increased water vapor and more substantial lower-level convergence were present over TRSR during 2002-2015. This marked interdecadal variability in TRSR precipitation responded to the position of the large-scale forcing-East Asian Westerly Jet (EAWJ), which significantly modulated the low-frequency variability associated with Southern Oscillation Index (SOI). 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 is −0.446, p<0.05 by student’s t-test) correlated with the precipitation over the TRSR, implying southward years of (northward) EAWJ is associated with intensifying (weakening) TRSR summer precipitation, whereas the intensity of EAWJ is insignificantly correlated with TRSR summer precipitation.