中文摘要：

基于长江中下游流域75个雨量站1960~2012年的日降水资料,通过定义长、短周期旱涝急转指数,全面地分析了长江中下游流域旱涝急转的趋势变化和时空分布特征。研究结果表明：（1）长周期旱涝急转表现为以涝转旱事件为主,且存在由旱涝急转事件向全旱或全涝事件过渡的趋势,短周期的旱涝急转发生频率较高的也是涝转旱事件;（2）长江中下游北岸多发生旱转涝事件,南岸则多发生涝转旱事件;（3）1998年和2011年6~7月短周期高强度旱转涝事件发生在长江北岸,涝转旱事件发生在南岸地区;5~6月与7~8月旱涝急转事件强度分布则呈相反状态;（4）总体来说,长、短周期涝转旱频次呈现不断减小的趋势,旱转涝有轻微增加的趋势。7~8月则较为特殊,湘江流域涝转旱有增加的趋势,洞庭湖地区涝转旱显著增加,此研究结果可以为长江中下游流域防洪抗旱工作提供一定的依据。

英文摘要：

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 droughtflood 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 2011occurred 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.