RAINFALL MULTIPLE TIME SCALE VARIATION RULE OF POYANG LAKE BASIN IN THE PAST 50 YEARS

A total of 49years of monthly rainfall data in 16meteorological stations in Poyang Lake basin during 1960to 2008 was analyzed by Morlet wavelet function.The rainfall seasonal,interannual and interdecadal time series analysis results were used to reveal the multiple time scale features of rainfall change,and the periodic variation and mutation points of rainfall sequences at different time scales.(1)Annual rainfall showed obvious interannual and decadal oscillations during 1960to 1990,no significant trend,but the annual rainfall had a significant increasing trend after entering the 1990s.The annual rainfall was decreasing from 2002.In general,spring rainfall had a decreasing trend during the study period and a decreasing amplitude of-11.03mm/10a;summer rainfall had an increasing trend and an increasing amplitude of 25.12mm/10a;autumn rainfall had a decreasing trend and a decreasing amplitude of-4.16mm/10a; winter rainfall had an increasing trend and an increasing amplitude of 11.85mm/10a.Annual rainfall had an increasing trend in Poyang Lake Basin and an increasing amplitude of 21.79mm/10a.(2)Both seasonal and annual rainfall had multiple time scale features,and there was 18afirst principal period in summer, winter and annual rainfall.Annual rainfall experienced three circulations from few to more on 18atime scales,and the mutational point happened in the year of 1970,1980,1992and 2003.At present,annual rainfall is in the less period.There is 6asecond principal period in spring,winter and annual rainfall.In additional,there is 3athird principle period in spring,autumn,winter and annual rainfall.(3)Summer and annual rainfall had the same trend and phase changes in the 18atime scale,while the spring and annual rainfall had similar trend and phase changes in 3aand 6atime scales.In 6atime scale,change rule of spring rainfall and annual rainfall was more similar than that of summer rainfall and annual rainfall.The corresponding relationship was different between changing pattern of spring and annual rainfall and that of summer and annual rainfall in different time scales,and smaller was the time scale,smaller was the phase difference.(4)The seasonal changes trend in the study period was followed the order of Springsummer autumnwinter in the 1960s,1970,1980and 2000s.Annual rainfall in the 1990swas obviously more than other periods,which was caused by that summer rainfall was greater than spring rainfall and winter rainfall was greater than autumn rainfall.