中文摘要：

干旱是我国发生最频繁、持续时间最长、波及面积最大的一种自然灾害。基于1961—2010年逐月平均气温和降水数据，应用标准化降水蒸散指数（SPEI）定量分析了商丘地区月尺度、季尺度和年尺度上的干旱发生频率和发生强度，揭示了该地区干旱发生的时空演变特征及干旱发生的原因。结果表明，SPEI值能够较好地反映商丘地区干旱的时空特征；随着时间尺度的增大，SPEI值波动幅度减小，干旱发生频率降低。近50年商丘地区历年、各季及月尺度均有干旱发生，干旱发生频率总体呈上升趋势，且各地区之间分布不均匀；四季中以冬、春两季干旱发生最为严重，其次为秋季。在干旱发生的年际变化方面，商丘地区在1966年、1968年和2008年发生了大范围的持续干旱。干旱发生强度分布呈现东部较高，中西部较低的特点。欧亚大气环流异常稳定、厄尔尼诺现象和气温的升高对干旱发生的贡献不可忽视。

英文摘要：

Owing to the precipitation distribution is very uneven and often accompanied by high temperature, so drought is one of the most frequent and enduring natural hazard that influences most area in China. In this paper, the drought occurrences were quantified by a new drought index, standardized precipitation evapotranspiration index （SPEI） based on the observed meteorological data of monthly mean temperature and precipitation from 1961 to 2010 in Shangqiu region. Based on the SPEI values of each station, the occurrence frequencies and severities of the meteorological droughts were computed and the annual, seasonal and monthly drought occurrence frequency and in- tensity over years were analyzed. The spatial and temporal evolution, intensity and the primary causes of drought occurrence in Shangqiu region were revealed. The results show that the SPEI values can effectively reflect the spatial and temporal evolution of drought occurrence. With the increasing time scale, the variation amplitude of SPEI decreases, and the frequency of droughts is reduced. In the recent 50 years, drought occurred in the annual, seasonal and monthly scales and the occurrence frequencies of drought showed an increasing tendency with quite uneven distribution regionally. Among the seasons and annual variations, the most serious drought happens in the winter and spring, followed by the autumn, and a wide range drought was occurred in 1966, 1968 and 2008. The intensity distribution of drought shows the high in the east and the low in the Midwest of Shangqiu region. The stable Eurasian atmospheric circulation, El Nino effect and the increasing temperature have a great influence on the drought occurrence in shangqiu region.