Analysis of July-August Daily Precipitation Characteristics Variation in Eastern China during 1958-2000

Daily precipitation data from 740 stations are used to analyze July-August precipitation trends and decadal variation in eastern China.The precipitation is categorized into four types according to the daily rainfall amount: 0.1-9.9 mm/d,10.0-24.9 mm/d,25.0-49.9 mm/d,and above 50.0 mm/d.Special attention has been devoted to their contribution to the total precipitation variation in eastern China.The results prove that total precipitation variation in eastern China is mainly due to the changes of torrential rain.The trend analyses show that the amount of precipitation,the frequency of precipitation,the frequency of extreme precipitation and the intensity of torrential rain have significantly increased along the Yangtze River valley and evidently decreased in North China during 1958-2000.Except for the frequency of precipitation,trends of other indices along the Yangtze River valley are greater than that in North China.The intensity of precipitation has coherently positive trend in eastern China however is not statistically significant in North China.The drought in North China results from the decrease of the frequency for light rain, with the maximum decreasing trend of-3%/10 a,the frequency and intensity of extreme precipitation in this area also have weak decreasing trends.The flooding along the Yangtze River valley in the past decades results from the increase of all sorts of precipitation frequency and intensity.The variations of precipitation frequency,intensity,extreme precipitation frequency and the maximum precipitation along the Yangtze River valley are out-of-phase with those in North China,as indicated by the significant negative correlations between the regional mean time series.The Mann-Kendall tests show that nearly all precipitation indices except the frequency along the Yangtze River valley and the intensity in North China have significant decadal shifts.In response to the decadal shift of East Asian climate in the late 1970s,the precipitation frequency of North China experienced a shift starting from the late 1970s,this kind of precipitation frequency shift is however not apparent along the Yangtze River valley.The decadal shift of extreme precipitation indices along the Yangtze River valley in the late 1970s are more significant than that in North China,with the shifts of precipitation intensity,extreme precipitation frequency and the maximum precipitation occurring around the late 1970s.