中文摘要：

干旱是当今人类面临的重大环境和气候问题之一。本文采用标准化降水蒸散指数（SPEI）研究渭河流域的干旱演变特征。基于渭河流域21个气象站点1960--2013年的实测降水、气温和日照时数数据，分别计算各站点年、季尺度的SPEI值，并分析了年尺度SPEI的变化趋势性；采用Mann-Kendall检验法、累积距平法和有序聚类法对SPEI指数进行综合突变检验；研究了渭河流域干旱覆盖面积、中度以上干旱分布特征以及连续干旱分布特征。结果显示：渭河流域年尺度的SPEI指数呈递减趋势，在1990年发生突变，干旱发生强度持续增强，1991～2013年干旱发生强度高于1960-1990年；1991—2013年各尺度的干旱覆盖面积除冬旱外均大于1960-1990年，且春旱在突变前后的变化最为剧烈；1991-2013年中度以上干旱发生频率明显大于1960-1990年，且连续干旱发生频率高于1960-1990年，表明自1991年起干旱程度在加剧。

英文摘要：

Drought is one of the major environmental and climate issues for humanity nowadays. A standard precipitation evapotranspiration index （SPEI） was used in this study to examine the drought evolution characteristics of the Wei River basin. Yearly and seasonal SPEI values have been calculated for each of the 21 meteorological stations in this basin, using the long series of precipitation, temperature and sunshine hours from 1960 to 2013, and the trend of yearly SPEI analyzed. We adopted methods of Mann-Kendall test, accumulative anomaly and ordered clustering to diagnose the mutation characteristic of yearly SPEI, and obtained a drought coverage and drought distribution characteristics of the basin. Results showed an overall decreasing trend in yearly SPEI with a mutation occurring in 1990, revealing a drought intensity increase in the basin from the level in 1960-1991 to a higher level in 1991-2013. The drought coverage for all the time scales in 1991-2013 except winter drought was higher than that in 1960- 1991, and especially it was subjected to more rapid changes in spring. In 1991-2013, the frequency of moderate to severe drought was significantly higher than that in 1960-1991 and the frequency of continuous drought was also higher, signifying a condition of drought intensifying since 1991.