Decadal Enhancement in the Effect of El Nino in the Decaying Stage on the Pre-Flood Season Precipitation over Southern China

The abundant precipitation over Southern China during the pre-flood season (PFS) [i.e., April-June (AMJ)] has important socioeconomic impacts on this densely populated region. Using observational and reanalyzed datasets, this study explores how El Nifio affected the subsequent PFS precipitation over Southern China during 1961-2020. The results show that the El Nifio-related anomalies in sea surface temperature forced a northwestern Pacific anomalous anticyclone (NPAAC) in the decaying AMJ. This NPAAC featured southwesterly wind anomalies in its northwestern flank, which could transport moisture from the South China Sea, and accompanying the NPAAC there was abnormal descending motion over the tropical western Pacific, resulting in weakened regional Hadley circulation with abnormal ascending motion over subtropical East Asia. Before the 1990s, this abnormal ascending motion was located mainly to the east of Southern China with insignificant impacts on the PFS precipitation there. In contrast, after the early 1990s, El Nifio-related warm sea surface temperature anomalies were stronger and longer-lasting with westward extension. This enhanced the NPAAC with a decadal westward extension, and consequently, the anomalous regional Hadley circulation was more evident over Southern China after the early 1990s during the El Nifio decaying AMJ, causing strong abnormal upward motion and excessive precipitation there. The present results emphasize an enhancing influence of El Nifio on the subsequent PFS precipitation over Southern China since the early 1990s, offering better understanding of the interannual precipitation variability over Southern China and with important implications for regional seasonal climate prediction.

Automated summary

This study explores the impact of El Nifio on pre-flood season precipitation in Southern China. The results show that El Nifio-related warm sea surface temperature anomalies contribute to the formation of an anomalous anticyclone, leading to increased rainfall in Southern China. The findings provide important insights into understanding precipitation variability in this region and have implications for seasonal climate prediction.