Extreme Rainfall over South China in April 2024 Associated with Early Indo-Pacific Ocean Capacitor and MJO Events

Abstract Climate conditions over East Asia are significantly affected by coupled ocean–atmosphere interaction in the tropical Indo-Pacific Ocean. In April 2024, South China suffered two rounds of extreme rainfall, occurring from 30 March to 6 April and from 19 to 30 April, resulting in the earliest flood over the Pearl River basin since 1998. This study finds that the early Indo–western Pacific Ocean capacitor (IPOC) effect and the Madden–Julian oscillation (MJO) jointly contributed to the extreme rainfall. Co-occurrence of El Niño and positive Indian Ocean dipole events in 2023–24 led to strong sea surface temperature (SST) warming in the western tropical Indian Ocean via wind forcings and oceanic waves. Such SST warming induced persistent easterly wind anomalies and maintained the anomalous anticyclonic circulation (AAC) over the western North Pacific. The IPOC effect was hence activated in April, approximately 2 months earlier than expected, inducing stronger northward water vapor transport. Moreover, two MJO events were observed in April. With the eastward propagation into the eastern Indian Ocean (phases 1–3), the MJO events facilitated the southwest flank of the AAC and enhanced the northward water vapor transport, leading to extreme rainfall along with strong convection in South China. This study emphasizes the synergistic contributions of climate modes on different time scales to extreme weather.