The Characteristics Of Drought And Flood In Spring And Summer Over Yangtze River Basin And The Association Studies With SST

The climatic characteristics of the whole Yangtze River is complexity, the eastern part of the region is the East Asian monsoon region, southwest lies in the region of southwest monsoon, Sichuan Basin is located in the Sichuan Basin, the Eastern is the TP monsoon region. With global warming, the characteristic of flood and drought in region become more and more complex, under the background of global warming, how change of the flood and drought in Basin are paid much attention. The147daily precipitations on the Basin are used in this work, we used the index Z, which are the best indicators for single station to present the drought and flood. Through using various climatic statistical methods to study the character of changing in drought and flood in different season over the whole Yangtze River Basin.Nearly50years, droughts and floods in the Yangtze River basin in different seasons are quite different, due to the flood and drought in summer have many factors, so the cumulative variance explained of10are less than65%, cumulative explained variance can reach80%in spring and autumn can reach70%, respectively, which reflect the difference of flood and drought in different season. But the sub-regions based on REOF are roughly the same, except for the eastern part of the Yangtze River in summer is divided into four zones, the rest of season can be divided into three sub-regions base on the high load vector of REOF. The remaining partitions are Sichuan Basin, southwestern Yangtze River and eastern TP area. The sub-regions based on flood and drought is roughly the same with the climatic regions. Due to the research of the characteristic of Flood and Drought based on REOF for different seasons, the conclusion can summarized follows:1) The characteristic of drought in spring:except the increase trend in the Western regions, the liner trend in other regions is reduced, while the increasing trend is the most significant. According to the high load vector of REOF, we can divide the whole Yangtze River Basin into six sub-regions in spring, in addition of mutations in the southwest region in the late1990s, the rest of the region mutation characteristic are not significant. And the other three sub-regions of the Yangtze River Basin in the east are in period of2-4years. In addition to the southeast of Basin, after1990s, there exist about four cycle. There is drought cycle about ten year in the southwest regions. 2) The characteristic of drought in summer:in addition to showing decreasing trend in the Sichuan Basin, the trend has significantly increased in other regions. The mutation take place in the mid1980s over TP, the south of Yangtze River in eastern of Anhui has a mutation in the early of1970s. Similarly in the eastern of River, There have2-4years cycle during1970s-1980s; the south and southeast of basin are same as in spring, after the1990s, exist around4-years cycle.The possible relationships between character of drought and flood over Yangzi River in spring and summer and SST are analyzed using SVD, respectively. In spring, when the SST increase over eastern equatorial Pacific and the western Pacific decrease, the northeast areas of Yangtze River tends to flood, while the western is drought. When the equatorial eastern Pacific SST is higher, the North pacific SST is low, the southeast of Yangtze River tends to flood, and the central region tends to drought. The Z index of Yangtze River in the summer is also studied with the early winter and early spring, the results show that form early winter to early spring, the higher value of coefficient are consistently. When the SST of eastern Pacific throughout the early winter is increasing, the eastern Yangtze River in the summer is tends to flood, when the SST rise in the eastern Pacific and the western is lowered, the northern part of Yangtze (northern Sichuan) tends to drought. The first mod is governed by the PDO, while the second mod is mainly affected by ENSO, and the same distribution of large values for right-field of the Yangtze River between early spring and winter, which depict that the effect of SST in early winter will continue until early spring. There are difference between the spring and summer, the ENSO of early winter is the mainly reason for the spring drought and flood in Yangtze River, while PDO is the mainly reason in the summer.