中文摘要：

根据甘肃省河东地区15个气象站点50年的气象资料，利用FAOPenman—Monteith模型和所提供的作物系数计算出各站点春玉米不同生育阶段的作物需水量，在此基础上计算出作物水分亏缺指数（cwDI），并划分河东地区的干旱等级，分析春玉米干旱发生的时空特征。结果表明：在春玉米生长季内，CWDI呈现先增大后减小的趋势，其中最大值出现在6月中下旬，且每旬的CWDI值均大于10％，即在作物整个生长季，降水都无法满足春玉米需水的要求。不同等级干旱发生的频率：轻旱8％～20％；中旱7％～23％；重旱0～17％；特旱0～47％。生长季内，河东地区春玉米干旱发生程度基本由南向北递增，不同生育阶段干旱的严重程度：抽雄一开花期〉拔节期〉乳熟前期〉出苗一七叶期〉乳熟后期一成熟期。近50年来，出苗一七叶期和拔节期的干旱有逐渐缓解的趋势；抽雄一开花期和乳熟前期干旱变化的趋势大致相同：20世纪60年代中后期及70年代初为干旱的严重时期，70年代中后期有所缓解，至今又有加重的趋势；乳熟后期一成熟期，近50年来干旱有加重的趋势。

英文摘要：

The total number of droughts is increasing in China due to global climate change. Extraordinary droughts are of a long duration, wide range and severe disaster degree. Eastern Gansu is located in the semi-arid-semi-humid climate zone, and is a rain fed agricultural region. Because the distribution of precipitation is uneven, the water requirements of spring maize are different during various growth stages. Understanding the temporal and spatial distribution and evolution of droughts during spring maize is important to the sustainable development of the economy. Here, according to 50 years of weather data from seven meteorological stations in eastern Gansu, the water requirements of spring maize at different growth stages was calculated using the FAO Penman-monteith model and coefficient. The crop water deficit index （CWDI） was calculated and the drought grade was divided into four communities. The results show that the CWDI became larger initially and then smaller during the growth period for spring maize; the ten days, middle and last ten days of June contained maximum values. The CWDI of every ten days was over 10%, showing that precipitation in the growth period cannot meet the water requirements of spring maize. The frequency of different classes of drought were 8%-20% for light drought, 7%- 23% for middle drought, 0-17% for heavy drought, and 0-47% for excessive drought. The relative severity of the drought followed the pattern： tasselling stage to flowering stage 〉 jointing stage 〉 pre-milk stage 〉 emergence stage to seven leaf stage 〉 late-milk stage to mature stage. In the last 50 years, the severity of droughts has increased in this area.