中文摘要：

研究旱涝急转现象对于区域农业生产以及夏季防汛抗旱等工作具有重要意义。根据山西省16个气象站1961—2013年5—8月逐月降水资料,计算了夏季旱涝急转指数（DFAI）,采用线性倾向法、M-K突变检验以及反距离权重空间插值法等方法分析了夏季旱涝急转事件的时空演变特征。结果表明：在年代际变化上,山西省夏季DFAI呈现不显著下降趋势,在1970年代前后分别以旱转涝和涝转旱事件为主;DFAI强度呈不显著下降趋势,旱涝转换强度总体减弱。DFAI在5—6和7—8月的正/负值（负/正值）变化表示夏季降水的涝转旱（旱转涝）特征。DFAI强度分别在1978和2005年发生突变。典型旱转涝年（1976年）DFAI的高值区主要分布在山西东北部、中东部及西南部地区,而典型涝转旱年（2002年）DFAI绝对值的高值区则主要分布在山西省中部地区;DFAI变化率在空间分布上具有显著的南北差异。旱转涝事件主要分布在山西东北部、中西部以及西南部地区,而涝转旱事件在东北—西南方向上总体表现为多—少—多的变化特点。

英文摘要：

The research on abrupt alternation of drought and flood is of important significance to regional agricultural production and the campaigns of flood control and drought relief in summer. Summer drought-flood abrupt alternation index（ DFAI） is calculated based on the data of monthly precipitations in the summers of 1961-2013 recorded in the 16 weather stations in Shanxi Province. Spatio-temporal variation of the abrupt alternations of drought and flood is characterized through Linear Tend Analysis,Mann-Kendall Test and Inverse Distance Weighted Interpolation（ IDW） of the data.Results show as follows：（ 1） The overall variation of DFAI in Shanxi Province during the period presented an insignificant declining trend. The events of abrupt shift from flood to drought or vice versa occurred mainly around the 1970 s,and during that period of years DFAI intensity also exhibited an insignificant declining trend which means the events of droughtflood abrupt alternation decreased in intensity;（ 2） DFAI is an index that reflects changes in precipitation in the summer periods from May to June and from July to August in Shanxi Province. The positive/negative values or negative/positive values of DFAI during the periods of May-June and July-August indicated shift from flood to drought or vice versa during the summer periods;（ 3） DFAI and DFAI intensity experienced abrupt change in 1978 and 2005,respectively.（ 4） In1976,a typical year of abrupt shift from drought to flood,the regions high in DFAI were found in the northeastern,central eastern and southwestern parts of Shanxi Province,while in 2002,a typical year of abrupt shift from flood to drought,andthe regions high in absolute DFAI value were in the central part of Shanxi Province. Spatially,the variation of DFAI exhibited a sharp difference between north and south of the Province.（ 5） The events of abrupt shift from drought to flood occurred mainly in the northeast,middle-west and southwest of Shanxi Province,while those from flood to drought disp