Statistical Analysis Of Climatic Variation Features And Spatial And Temporal Distribution Of The Flood And Drought In Zhejiang Province

In this paper, the climatic variation features and spatial and temporal distribution of the flood and drought in Zhejiang Province were analyzed by using 36 monthly and seasonal station data during 1961-1999 observed over Zhejiang province, 160 rainfall and temperature data during 1951-1999 observed over China, northern hemisphere 500mb height data during!961-1999, the planting and flood disasters area data in Zhejiang province during 1949-1998. We used many method: calculated trend coefficient of rainfall and temperature ,used EOF,REOF,SSA(singular spectrum analysis) and MEM(maximum entropy spectrum) method and synoptic method .We first studied the climatic variation features of summer and autumn and characters of the flood and drought in Zhejiang. Result shows that the trend of precipitation in summer is increasing, the temperature in summer has no trend; the trend of precipitation in autumn is decreasing, the precipitation during September represent its feature, the trend of temperature in summer has no trend, but in some region, we can find out prominent trend.Analyses from singular spectrum and maximum entropy spectrum techniques reveal that summer and autumn precipitation have 10-year periods, and about 2.5-year oscillations are particularly pronounced for the autumn precipitation. We classified flood and drought years of summer and autumn, It is pointed out in the paper that there are circulation anomaly in 500mb height field before flood or drought years .we also find out that there are intimated relation between autumn floods and droughts of Zhejiang province and the macro-scale rain belt.The meteorological elements emergence abnormal features in summer before flood and drought years .We make out predictor to predicate summer precipation.REOF analysis was carried out for summer and autumn rainfall field over Zhejiang province. The results indicate that the rainfall fields spatially are classified 3 subregions in summer and autumn, but they include some different place in each subregion. In summer, there are least precipitation in north region and most precipitation in south-east region. Observed by season or by month, we can see clearly that there are prominent positive trend in north region, the frequency of abnormal precipitation appears in three region are different, south-west region is the most likely place to suffer floods and droughts. The frequency of the flood and drought has distinct interannual change, floodsemergence more and more from 1980, especially in north, there are more and more droughts in north region and no flood from 1980.In autumn, there are least precipitation in south-west region and most precipitation in south-east region ,the precipitation difference between them is exceeding 95% significance level, the difference between them is most prominent in September. The precipitation decline from September to November.The frequency of autumn flood and drought have distinct interannual changes, the trend in north and south-west region is declining and in south-west is increasing from 1990.In this paper, we study the climatic variation features of all the year ,spring and winter, result shows that the precipitation in Zhejiang province has no prominent trend in spring and winter. The precipitation of the year has 10 year periods ,2.5-year oscillations have large variance in he precipitation of spring ,winter and the year, especially in winter ,the variance reach 36.3%.The trend of temperature is positive in all the year, increasing in north region is very prominent, this trend conform to the temperature increasing trend of the northern hemisphere. Temperature increasing appears most in spring and winter .The possibility is great (roughly 80%) for large-scale floods and/or droughts to be in the province on an annual basis. It is evidenced that the seasonal disasters hit the study region each year after 1985. The annual and seasonal calamities experience inter-decadal variation, and the climatic frequency of their occurrence shows noticeable change, especially in sum...