The Comparison Analysis of Flood and Drought Features Among the First Flood Period in South China,Meiyu Period in the Yangtze River and the Huaihe River Valleys and Rainy Season in North China in the Last 50 Years

Based on the Chinese 160 stations monthly precipitation supplied by the National Meteorological Information Center of China,the distribution features of floods and droughts events during the first flood period in South China,the Meiyu period in the middle and lower reaches of the Yangtze River and the Huaihe River valleys and the rainy season in North China are analyzed respectively and compared with each other by using the droughtsfloods indices for the period of 19512000.The interannual and decadal variations of the three types of rainfall are also investigated by the DB-16 wavelet analysis method.The correlation analysis is applied in finding the features of the atmospheric circulation in the same term and sea surface temperature(SST) in the preceding months which are linked with different kind of rainfall.Results show: in the last 50 years,the frequency of floods events is nearly the same as that of the droughts,and the intensity of floods is greater than that of droughts in South China and the Yangtze River and the Huaihe River valleys,whereas North China has the similar intensity of floods and droughts,associated with a drought tendency in South China and North China and a flooding tendency in the Yangtze River and the Huaihe River valleys;the first flood period in South China has the most remarkable annual variation,the Meiyu has the second and the rainy season in North China has the weakest,but the decadal variation is just opposite;according to the 500 hPa height field of the same term,the first flood period of South China has a close relationship with the low value systems at its north side while the Meiyu and the rainy season in North China are greatly influenced by the western Pacific subtropical high.The Meiyu also has a significant positive correlation with Okhotsk Blocking High and the rainy season in North China is mainly affected by the circulation systems on its northwest side;the rainy season in North China is closely related to the SST in Atlantic and North Pacific,while the SST in the adjacent sea of China has a strongest influence on the Meiyu of the Yangtze River and the Huaihe River valleys and the first flood period in South China has the most tremendous relationship with the SST near the Bay of Bengal.The emphasis of this paper is concentrated on the features summary of the three types of rainfall in East Asia.The East Asian summer rainfall is a very complex phenomenon and very important for the agriculture,industry and people's life.This work attempts to offer some references for the prediction of the East Asian summer monsoon rainfall.