Determination of the major moisture sources of cumulative effect of torrential rain events during the preflood season over South China using a Lagrangian particle model

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. Key Points Indian Ocean water vapor transport accounted for more than 33% of all precipitation formed during cumulative effect of torrential rain (CETR) events In the 1990s, water vapor transport from the Indian Ocean increased significantly, while water vapor transport from the western Pacific Ocean significantly declined The spatial distribution of rainfall occurring during South China CETR events was associated with different forms of anomalous water vapor transport Plain Language Summary The Lagrangian particle dispersion model (Hybrid Single‐Particle Lagrangian Integrated Trajectory 4.9) was used to simulate the trajectories of air parcels involved in 66 CETR events over South China from 1979 to 2014. Then,the “areal source‐receptor attribution” method was used to quantitatively compute the contributions of each water vapor source region. Fin