Extreme Precipitation in the South China Sea and Surrounding Areas: Observation and Projection

The South China Sea and its surrounding areas are among the most sensitive regions and are characterized by strong sea–land–air interactions. Extreme precipitation patterns over the region have garnered extensive attentions in recent decades, which significantly affects global climate variabilities by providing substantial energy and moisture for global atmospheric circulation. This study utilizes gauge-based gridded data and a statistically downscaled CMIP6 (the sixth phase of the international Coupled Model Inter-comparison Project) dataset to systematically investigate the historical and future spatiotemporal characteristics of maximum 1-day precipitation (RX1day), maximum 5-day precipitation (RX5day), very heavy precipitation days (R20), and very wet days (R95p) over this region. The indices RX1day, RX5day, R20, and R95p are commonly used to represent heavy rainfall, persistent heavy rainfall, high-frequency heavy rainfall, and accumulated heavy rainfall, respectively. Our findings reveal that these four indices share a similar spatial pattern from 1951 to 2014 on annual and seasonal time scales. Large values of the indices are recorded over Southeast Asia, Southern China, and the southern part of the Tibetan Plateau. In other words, these regions not only experience heavy rainfall but also exhibit sustained and high-frequency heavy precipitation events. The four indices exhibit large values over Southeast Asia across all seasons. They also exhibit high (low) values over South Asia, the Tibetan Plateau, and East Asia during summer (winter). The projected future patterns of these indices maintain their historical spatial counterparts. Moreover, the four indices averaged over the entire region exhibit increasing trends from 2015 to 2100 under the SSP1-2.6 and SSP5-8.5 scenarios. The percentage changes in the indices from 2016 to 2035, 2046 to 2065, and 2080 to 2099 under the two scenarios exhibit a slight decrease in Southeast Asia and East Asia compared with 1995–2014. However, the percentage changes increase over South Asia and the Tibetan Plateau. In addition to these findings, we explore the physical mechanisms associated with extreme precipitation over Southeast Asia. We find that the extreme rainfall patterns observed over Southeast Asia can be attributed to various sea surface temperature anomalies (SSTAs). Cold SSTAs over the Indian Ocean result in dry conditions in the south and wet conditions in the north. Meanwhile, warm SSTAs over the tropical North Atlantic lead to overall wet conditions across Southeast Asia. Finally, SSTAs over the tropical Pacific and Atlantic chang this pattern, with dry conditions in the north and wet conditions in the south.