根据西安市1951年－2013年气象资料确定可利用降雨量的Z指数以表征气象干旱强度，并将干旱强度划分为7个等级。分析该地区的干旱特征，发现：从季节尺度的长期变化趋势来看，干旱主要出现在春、夏、冬三季，四个季节均向干旱方向发展；西安干旱强度在63年中总体呈上升趋势，20世纪90年代以后干旱频率和强度较之前均有较大提升；从干旱趋势突变分析的结果来看，突变年份为1957和1958年，1965年后只存在向偏旱方向发展的趋势并且在1997年之后更加显著。通过与Palmer指数法和传统Z指数法对西安典型干旱年份的评估结果对比，认为可利用降雨量Z指数法对西安市气象干旱特征的分析具有较强的客观性。

According to the meteorological date in Xi’an city from 1951 to 2013, the Z index of available rainfall was calculated to propose the characterization of drought strength, which was divided into 7 levels. From the results of analyzing the drought characteristics in city, we find that: (1) Drying appears in spring summer and winter, and every season shows a drying trend according to seasonal difference of drought. (2) The annual Z index shows an increasing trend in 63 years. The frequency and strength of drought have increased remarkably since 1990s. (3) Mann-Kendall test shows that the sudden change years were 1957 and 1958, and drying trend has been existing since the year of 1965 and became more significant since 1997.By comparing with the Palmer index and traditional Z index’ assessments of the typical years’ drought period, the objectivity of the analysis’ results are certified.

水利部公益性行业科研专项经费项目（201301084）