Interannual Variation in Moisture Sources for the First Rainy Season in South China Estimated by the FLEXPART Model

The first rainy season (April-June) of South China includes the phases before and after the onset of the South China Sea summer monsoon (SCSSM). Abundant moisture supply is the key dynamic process for precipitation formation. Thus, we employ the FLEXPART model to explore the corresponding moisture sources for the two phases. Before the onset of SCSSM, land regions contribute more moisture to the precipitation over South China than the ocean sources. The main source regions are Southeast Asia (27.01%), the South China Sea (25.96%), South China (11.12%), and the southern part of the northwestern Pacific (10.23%). Land sources (66.87%) play a more important role than ocean sources (33.13%) in the interannual variations, with the contributions mainly from Southeast Asia (47.56%) and the South China Sea (28.79%). After the onset of SCSSM, the climatological contribution of ocean sources is larger than that of land regions, and the main source regions are the South China Sea (20.78%), Southeast Asia (17.51%), the Bay of Bengal (13.76%), and South China (11.21%). For the interannual variations, the contributions of land sources and ocean regions are comparable, and mainly from Southeast Asia (33.53%) and the Bay of Bengal (32.26%). The moisture transports for the interannual variations in first rainy season precipitation over South China before and after the onset of SCSSM are significantly correlated with the east-west contrast of sea surface temperature anomalies over northern part of North Pacific and the uniform warming over Indian Ocean, respectively. This study provides important guidance in improving the regional precipitation predictions and understanding the water resources changes.

Automated summary

The study reveals that before the onset of the South China Sea summer monsoon, precipitation in South China is mainly sourced from land regions, while after the monsoon arrival, ocean sources play a larger role. Southeast Asia and the South China Sea are the primary moisture sources in both phases.