Abstract:

Based on the daily precipitation data in the flood seasons (from April to June) During 1960-2011 from 83 stations in Jiangxi Province，the extreme precipitation threshold values for all stations were determined firstly.Taking 95 percentiles as threshold value of precipitation events，the extreme precipitation event frequency in flood season was counted and their temporal and spatial characteristics were analyzed by use of five main methods including EOF，REOF，trend analysis，moving ttest analysis and Maximum Entropy Spectral analysis.The results showed that geographical distribution of extreme precipitation threshold was characterized by increasing from west to east and from south to north in Jiangxi province.The frequency of extreme precipitation event was 3-5 times，and most regions was about 4 time.The areas in which the extreme precipitation events often occurred were mainly concentrated along the ZhejiangJiangxi railway.The average frequency of extreme precipitation in flood season of Jiangxi appeared to be a growth trend，and it also showed a large interannual difference.The extremely precipitation events frequency anomaly in flood season over Jiangxi was positive in early 1960s，from late 1960s to mid1970s，in middle and late 1990s，and was negative in mid1960s，from late 1970s to early 1980s，from midlate 1980s to early 1990s.EOF analysis showed that the ratio of the front 5 eigenvectors with the contributing rate of cumulative sums of squared was 63.8%，which passed the significant level test according to the NORTH method.Consistent anomaly distribution was the main spatial mode of extreme precipitation event frequency in Jiangxi Province，and the variance contribution rate of the first mode was 34.5%.The spatial distribution of extreme precipitation event frequency was complex with anomaly difference between the north and the midsouth of Jiangxi.REOF analysis manifested that extreme precipitation fields in Jiangxi could be divided into five main regions.In all of the representative stations，region Ⅰ did not have a very significant growth or decline change，but it came through fewmorefew change; region Ⅱ，region Ⅲ and region Ⅴ had a rather weak growth trend; region Ⅳ had a rather weak decline trend in the recent 52 years.The moving ttest analysis showed that two of the five subregions appeared significant abrupt changes in extreme precipitation frequency.There were abrupt changes in Yushan in 1976 and 1986，and Yongfeng in 1974 and 1984 for the extreme precipitation event frequency.The other three representative stations did not have significant abrupt changes in extreme precipitation frequency.The Maximum Entropy Spectral analysis showed that 65 and 26 years period was significant in region I; 2—4 years period was significant in region Ⅱ; the major notable cycle was basically the same in regions Ⅲ and Ⅳ，including main periods of 3—4 years; 3.2 years period of interannual variation and 13 years period of interdecadal variation were significant in region V.The preceding SST over equator east Pacific Ocean had significant impact on extreme precipitation events in flood season of Jiangxi.The extreme precipitation event frequency in flood season had obviously isotopic distribution with the preceding MayJune and winter SST over equator east Pacific Ocean