Prediction of the Distribution of the 2012 Summer Rainfall in China and Analysis of the Cause for Anomaly

The observed and predicted 2012 precipitation in China is reviewed. The distribution of the observed summer precipitation shows flooding in northern China and drought in the Yangtze River basin. The main rain band is located in the Yellow River basin and north of that region. Areas of abnormally positive precipitation anomalies are mainly located in northwestern China, Mongolia, and the area around Bohai Gulf, whereas areas of negative precipitation anomalies are located in the Huaihe River and Yangtze River basin, especially the Jianghan to Huaihe region. The main predicted rain band is located in the region from southern North China to the Huaihe River, which is to the south of the observed rain band. Further analysis of the reason behind the extremely heavy northern summer precipitation shows that the blocking high was strong over mid–high latitudes in Eurasia in the summer of 2012, whereas the Northeast China cold vortex was frequent and the 500 hPa geopotential height field over the mid–high latitudes showed the pattern of +-+ from west to east. However, there is no correlation of floods in the Yangtze River basin and atmospheric circulation. The floods are primarily attributed to the abnormally strong East Asia summer monsoon, whereas the western Pacific subtropical high(WPSH) moves northward causing the cold and warm air to meet, which leads to positive precipitation anomalies in the north. Furthermore, the analysis suggests that the position of the main rain belt in the summer depends on the location of the interaction between cold and warm air, which is influenced by the different configurations of the blocking high over Eurasia at mid–high latitudes, the northeast cold vortex, the East Asia summer monsoon, and the WPSH. Finally, by combining quantitative calculations with qualitative judgment, the most similar and most opposite year to the summer precipitation of 2012 were selected and the three-year differences for the SST and the main members of the summer monsoon circulation system of East Asia were analyzed. In 1959, which a year most similar to 2012, the SST and key elements of the East Asia summer monsoon system do not show obvious abnormal signals, whereas it shows approximately opposite features compared to 2012. In 1980, which a year much different than 2012, the features of SST and key elements of the East Asia summer monsoon system are opposite compared to 2012. These features reflect the decadal variations in the summer rainfall in China and the main factors affecting it; that is, the SST and the East Asia summer monsoon system.