Impacts of the SST Warming Trend and Natural Variability on the Summer Extreme Precipitation Intensity of the Middle and Lower Reaches of the Yangtze River

For years, floods and waterlogging caused by extreme precipitation have brought enormous economic losses and substantial human casualties to China. Global warming has increased the frequency and intensity of extreme precipitation events. However, the contribution of global warming to extreme precipitation events in different regions remains uncertain. On the basis of the water vapor budget characteristics of summer extreme precipitation events over the middle and lower reaches of the Yangtze River (MLYR) in China, the effects of the SST warming trend and natural variability forcing on the intensity of typical extreme precipitation in this region were investigated. The results show that (1) extreme precipitation and summer processes are accompanied by the convergence of water vapor throughout the atmosphere, and the convergence occurs in the meridional direction. The anomalous anticyclonic circulation over the Northwest Pacific formed a stable moisture transport with anomalous southwest winds at the southern boundary of the region. (2) In the summer, when typical extreme precipitation occurs, the SST is strongly positive in the equatorial Indian Ocean and the tropical Atlantic Ocean, mainly contributing to the warming trend, while SST anomalies in the equatorial middle eastern Pacific result from La Niña. (3) The numerical sensitivity tests of the SST warming trend and natural variability show that the regional moisture convergence forced by the SST warming trends in 1998, 2017, and 2020 was 83%, 210%, and 107% of the natural variability forcing, respectively, so the SST warming trend is more important than the natural variability. (4) The SST warming trend and natural variability are caused by the anomalous anticyclonic circulation over the Northwest Pacific Ocean, which causes anomalous water vapor transport over the southwestern boundary of MLYR , leading to the occurrence of extreme precipitation.