Spatial And Temporal Features Of Precipitation Extremes In Association With Circulation Changes In Eastern China Over The Past Five Decades

Using daily rainfall data of 90 stations in the eastern part of China from 1960 to 2009 and NECP-NCAR reanalysis from 1970 to 2009, the long term trend, interdecadal changes of occurrences and intensity of precipitation extremes along with the circulation characteristics of regional extreme precipitation of each separated subdivision in the eastern part of China in recent five decades have been investigated. Our results show that:1) In recent 50 years, both in summer and winter, the occurences of daily extreme precipitations are increased, and the precipitation intensity of extremes are become stronger. In atutmn there is a decrease trend in both the frequency and the intensity of extreme daliy precipitation events. The Middle-lower Yangtze River vallay is a region with notable seasonal differences of the changes of extreme daily precipitations. In summer and winter seasons the notable increases whereas in autumn and spring the notable decreases are found in the occurrences of extreme daily precipitation events. The interdecadal changes are more significant in summer in comparison with those in other three season.2) Further analysis of the interdecadal changes of precipitation extreme events in summer show that:There are significant interdecadal changes of precipitation extremes in the past 50 years. In recent 20 years, the precipitation extremes occurred more frequently than those in the earlier 30 years, and more stronger extreme precipitation events were observed in 1990s. In the eastern part of China, the extreme events of precipitation processes last usually less than 9 days. However, the extreme events of continuous rainy days last usually more than 9 days. Fujian province other than other regions in the eastern part of China is a place where more precipitation processes with higher persistence and stronger intensity occur. The place where the largest extreme rainfall appear is found in conjunction part of Jiangxi and Anhui provinces. Zones where the extreme events of precipitation occur more frequently moves interdecadally in meridional direction. The north-south shifts of the zones mentioned above are also observed in daily precipitation events and the extreme events of precipitation processes. In the 1990s is the decade with higher frequency in the all four class of extreme precipitation events in the southern region next to Yangtze River. And this made those two zones of frequent occurrences of extreme events of precipitation south of and north of Yangtze River being connected. So in the last three decades the two zones seemingly get closer to each other and even merge into one in some decades, and get distant from each other in other decades.3) The occurence of regional extreme rainy days in the five subdivisions in the east China is somehow related to rain belt migration in meridional in summer time in east China. In the subdivisions located south of Yangtze river, the precipitation extremes occurs in June while in the subdivision located in Huaihe river valley there occur the precipitation extremes in July. In the northernmost subdivision of eastern part of China there occur more extreme precipitation days in August.Regional mean precipitation extremes in the subdivisions in the eastern part of China tend to occur more frequently in 1990s and less frequently in the 1980s.For any extreme events of regional mean precipitation in all five different subdivisions, there observed a anomalous cyclonic circulation in the left side of the extreme precipitation reigion and an anti-cyclonic circulation in the right side of the region in the middle-lower troposphere. It seems that the location and intensity of northwestern Pacific subtropic high play and important role in the occurrences of the regional mean extreme precipitation events these in subdivisions in the eastern part of China.The water vapor is transported in the extreme precipitation events mainly from South China Sea and the west Pacific. However, for the precipitation extremes in Huanghuai subdivision, the water vapor seems nothing to do with South China Sea. The positive anomalous diabatic heating - is observed in the northern flank of the rainbelt for each different subdivisions.