Roles of moisture sources and transport in precipitation variabilities during boreal summer over East China

The roles of moisture sources and transports in the interannual and interdecadal precipitation variabilities during boreal summer over three subregions of East China, namely, South China (SC), the middle and lower Yangtze River valley (YRV), and North China (NC), are complex and different. In this paper, ERA-Interim reanalysis data collected 4 times per day from 1979 to 2017 are used to analyze the roles of moisture sources in the interannual and interdecadal variabilities in summer precipitation over the three subregions of East China. Using the hybrid single-particle Lagrangian integrated trajectory model, six atmospheric moisture sources, land area source (LD source), East China source (EC source, except for the target region), Indian Ocean source (IO source), Pacific Ocean source (PO source), South China Sea source (SCS source), and regional evapotranspiration sources (SC source, YRV source, and NC source), are defined. The precipitation of the IO and SCS sources accounts for 43.73% and 23.45% of the SC summer precipitation, respectively, thus dominating the interannual and interdecadal variabilities in the SC summer precipitation. For the YRV, the summer precipitation is influenced by the EC source precipitation (22.41%), YRV source precipitation (23.97%), IO source moisture (27.78%) and SCS source moisture (14.40%). The interannual and interdecadal variabilities in precipitation are influenced by all moisture sources except the LD source and PO source moisture transports. The land evapotranspiration, which includes the EC source moisture (39.04%) and NC source moisture (22.04%), is the major source of moisture for summer precipitation over NC. In addition, the westward moisture transport from the PO source does not directly arrive in East China during El Nino events. Simultaneously, most of the northward moisture is released over the western YRV. Warming in the tropical Indian Ocean is responsible for decreases in precipitation from the IO source, PO source, and SCS source. In addition, the significant increase in the PO source precipitation over the eastern YRV and the significant decrease in the IO source precipitation over the western YRV were induced by the Pacific decadal oscillation phase transition from warm to cold in approximately 1999.