Advances of Research and Application on Major Rainy Seasons in China

The pre-rainy season in South China, Meiyu, rainy season in North China and autumn rainfall in West China are important phenomena influenced by the process of the East Asian summer monsoon (EASM). These regional rainy seasons determine the distribution and evolution of drought and flood during the flood season over mid-eastern China. Therefore, the prediction of regional rainy seasons plays an important role in the meteorological service of flood season.The research progress on characteristics and influencing factors of major rainy seasons during flood season in China are reviewed. In order to meet the demand of prediction operation, the influence and mechanism of the previous sea surface temperature (SST) and related atmosphere circulation systems on climatic events are analyzed firstly, and the statistical prediction models can be established based on that.Recent studies show that SST anomalies (SSTAs) are important forecast signals of rainy seasons. However, the influence and spatial-temporal pattern of SST vary with the interannual and interdecadal variation characteristics of different events. For instance, the interannual variation of precipitation in the pre-rainy season in South China can be better explained using the east-west SST contrast index in the tropical Pacific. Multiple timescale variation characteristics of Meiyu over the Yangtze River correspond to different SST forcing. Key regions of SST associated with interannual variation of Meiyu over the Yangtze River are in tropics. For the interdecadal or mutli-decadal time scale of Meiyu variations, the SST in middle and high latitudes may play an important role. The intensity of rainy-season precipitation in North China is not only coincident with the ENSO phase-switching, but also influenced by the developing speed of ENSO event. The key SST region that influences autumn rain in West China has changed with the inter-decadal changing background, which requires updating impact factors and models.These results provide strong support for the real-time prediction of climate events in recent years. During 2015-2018, the prediction accuracy of the onset date and intensity (rainfall) of Meiyu and rainy season in North China is 75% and 81%, respectively.