SPATIAL AND TEMPORAL VARIATION ANALYSIS OF RAINSTORM DAYS FOR LAST 50 YEARS IN THE YANGTZE RIVER CATCHMENT

Using the daily rainfall data of 178 stations from 1961 to 2010and the DEM data of Yangtze River Basin,the spatial and temporal variation of the frequency of annual average rainstorm days during the last50 years in the Yangtze River Basin were analyzed with the Mann-Kendall trend test,coefficient of variation analysis and the GIS spatial analysis methods.The results showed that:there is a spatial tendency that the frequency of annual average rainstorm days is declining from East to West in the Yangtze River Basin,and gradually reduced as the altitude increases,showing significantly negative correlations;influenced by the plateau climate on upstream reaches of the Yangtze River Basin,the frequency of average annual rainstorm days is less than one day,and the spatial distribution of annual average rainstorm days in the upper-middle reaches of the Yangtze River Basin is mainly affected by the humid subtropical climate;with increasing latitude,the starting time of rainstorms is delayed,but the end time moves forward,and the duration of the rainstorm have a decreasing trend;coefficient of variation of annual rainstorm days and annual average rainstorm days showed an exponential relationship,their correlation coefficient was 0.97.In a large number of annual average rainstorm days(small)local coefficient of variation is small(large);the variation of annual average rainstorm days in the central of the middle-lower reaches of the Yangtze River Basin and the Sichuan Basin and its surroundings present a decreasing trend,other areas showed an increasing trend for varying degrees;while the river systems of Poyang Lake,Sichuan Province(the cities of Ya'an,Emeishan and Wanyuan),Hunan Province(Anhua County and Nanyue District)and Hubei Province(Honghu City and Yingshan County)have many rainstorm days with less coefficient of variation,and just because of this,it faces a lot of pressure in order to cope with floods and geological disasters;and the research could help the government to acknowledge the mechanism of flood disasters in the Yangtze River Basin,and to improve the ability of prediction and precaution.