Dynamics of Late Spring Rainfall Reduction in Recent Decades over Southeastern China

Abstract

Since 1951, late spring (May) rainfall over southeastern China (SEC) has decreased by more than 30% from its long-term average, in contrast to a rainfall increase in boreal summer. The dynamics have yet to be fully determined. This paper shows that as the Indo-Pacific enters into a La Niña phase, significant negative mean sea level pressure (MSLP) anomalies grow over the Indian Ocean and the western Pacific sector. The associated large-scale southwesterly anomalies transport moisture to the nearby South China Sea and the SEC region, contributing to a higher rainfall. A presence of a Philippine Sea anticyclonic (PSAC) pattern, arising from a decaying El Niño, strengthens the rain-conducive flow to SEC, but it is not a necessary condition. During the past decades, an increase in protracted El Niño events accompanied by a reduction in La Niña episodes has contributed to the May rainfall decline. The extent to which climate change is contributing is discussed.