Aanlysis on Variation Feature of Drought in Mid- and Lower-Reaches of Yangtze River Basin

The characteristics of spatial and temporal variations of drought in mid-and lower-reaches of Yangtze River basin(24°~35°N,104°~124°E) were statistically analyzed based on the observed data at 180 stations using the meteorological drought composite index from 1969 to 2008 and Z-index of 3 representative stations from 1953 to 2008,respectively.The results show that the coverage area of drought over 90% mainly occurred in winter before 1980s,in spring in 1990s and in summer in 21 century.The drought frequency decreased in spring and autumn and increased in winter and summer.The local drought events increased in winter in mid-and lower-reaches of Yangtze River basin due to the drought frequency were high though the coverage area of drought reduced.The drought and flood occurred frequently in summer because the coverage area of drought were big nevertheless the frequency of drought were lower.The drought events reduced in spring as the coverage area of drought were decreasing and the light drought dominated.The drought events in autumn were the minimum as a whole.