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In this paper, reanalysis data collected by ERA‐Interim 4 times daily from 1979 to 2014 are used to analyze the main atmospheric moisture sources of cumulative effect of torrential rain (CETR) events during the preflood season (1 April to 30 June) over South China. Using a Lagrangian particle dispersion model—the Hybrid Single‐Particle Lagrangian Integrated Trajectory model—the major atmospheric moisture sources of 66 CETR events for the period of 1979–2014 are identified and compared. In this study, five atmospheric moisture sources—the land area, Indian Ocean, Pacific Ocean, South China Sea, and South China—are defined, and the effects of these moisture sources on preflood season CETR events over South China are quantitatively estimated. The results indicate that during the preflood season, Indian Ocean water vapor transport accounts for 30% of the atmospheric moisture generated in CETR events, thus dominating precipitation over South China. The water vapor transport from the land area (14%), western Pacific Ocean (10%), South China Sea (25%), and South China (20%) also play important roles in preflood season CETR events. Furthermore, a significant transition in water vapor transport occurred in the 1990s, during which water vapor transport from the Indian Ocean increased significantly, while water vapor transport from the western Pacific Ocean significantly declined. In addition, a significant positive anomaly in Pacific Ocean and South China Sea water vapor transport spurred CETR events in the east, while a significant positive anomaly in Indian Ocean water vapor transport facilitated CETR events in the west.

The roles of moisture sources and transport in intraseasonal precipitation variabilities during the preflood season over South China are complex and different. In this paper, ERA‐Interim reanalysis data that were collected four times daily from 1979 to 2017 are used to analyse the variation and influence of moisture transport in intraseasonal precipitation during the preflood season over South China. Using the Hybrid Single‐Particle Lagrangian Integrated Trajectory model, fixed atmospheric moisture sources are defined: land area source (LD source), Indian Ocean source (IO source), Pacific Ocean source (PO source), South China Sea source (SCS source), and South China source (SC source). Sea source moisture transport accounts for more than 75% of the total precipitation during the preflood season, which is the most important moisture source in South China. For April, southeasterly moisture transport, which includes PO source and SCS source moisture transports, is the major moisture transport over South China. Then, the IO source and SCS source precipitation increased significantly during May. During June, the IO source precipitation accounted for 43.75% of the total precipitation, thus dominating precipitation over South China. In addition, there is a significant difference in the interdecadal variation in the preflood season precipitation before and after the Indian summer monsoon onset. Before the Indian summer monsoon onset, the land‐sea thermal contrast decreased, which led to a significant interdecadal reduction in the IO source, PO source, and SCS source moisture transports. After the Indian summer monsoon onset, the increase in IO source moisture transport is the primary cause of the interdecadal increase in precipitation over South China.

ERA-Interim reanalysis data from 1979-2017 are utilized to analyze the intraseasonal and interannual variabilities in the moisture transport associated with the summer rainfall over East China. Three key issues of moisture sources for East China summer precipitation are discussed in this study: the identi cation of the primary moisture sources of summer precipitation, determination of their individual contributions to the intraseasonal variation in summer precipitation, and determination of the extent to which each source affects the interannual variation in precipitation during the peak monsoon rainfall period (PMRP). Through the Lagrangian method, the water vapor is divided into six sources, namely, the land area source (LD source), East China source (EC source, except for the target region), Indian Ocean source (IO source), Paci c Ocean source (PO source), South China Sea source (SCS source), and regional evapotranspiration sources. This study proposes that the rainfall over South China (SC) during the PMRP is mainly in uenced by the IO source water vapor transport (52.4%). For the middle and lower Yangtze River valley (YRV), the rainfall contribution from southwesterly moisture transport accounts for approximately 50% of the total rainfall during the PMRP and determines the intraseasonal and interannual variation in the summer rainfall. The water vapor from terrestrial evaporation, which includes EC source water vapor (38.9%) and NC source water vapor (21.8%), is the most important moisture source for rainfall over North China (NC) during the PMRP.

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