Abstract: Based on the daily precipitation data from 75 rainfall gauging stations covering 1960-2012 in the middle and lower reaches of the Yangtze River Basin, the trend variation and temporal and spatial distribution characteristics of drought-flood abrupt alternation was analyzed by using long-cycle drought-flood abrupt alternation index(LDFAI) and short-cycle drought-flood abrupt alternation index(SDFAI). The results are as follows: 1) Flood to drought abrupt alternation events are the main performance of the long-cycle drought-flood abrupt alternation (LDAF), as well as the short-cycle drought-flood abrupt alternation (SDFA); 2) The north shore of the middle and lower reaches of the Yangtze River tend to occur drought to flood events, while the south shore tend to occur flood to drought events; 3) Intensive short-cycle drought to flood abrupt alternation events during June to July in 1998 and 2011 occurred in the north shore of the Yangtze River, and flood to drought events occurred in the south shore. However, intensity distribution of drought-flood abrupt alternation events during periods of May to June and July to August was just the opposite to that during June to July; 4) In general, both the occurrence of long and short-cycle flood to drought abrupt alternation events shows decreasing trends, while the drought to flood abrupt alternation events are on the rise. It is worth noting that the trend during July to August is somewhat special. Drought to flood abrupt alternation events are increasing in the Xiangjiang River Basin, and increasing significantly in the Dongting Lake region, which may provide a preferable reference for the work of the Yangtze River flood and drought management.

Key words: the middle and lower Yangtze River Basin, drought-flood abrupt alternation, spatio-temporal evolution