标准化降水蒸散发指数（Standard Precipitation Evapotranspiration Index, SPEI）是全球农业干旱监测应用最广泛的气象干旱指标之一。确定适宜的SPEI时间尺度是SPEI应用于农业干旱监测的前提。基于最新的全国土壤水再分析产品为参考，通过最大相关性分析确定了最适宜表征湖南省农业干旱的SPEI时间尺度，进而分析了湖南省1960—2014年间农业干旱的时空演变特征。结果表明：（1）全省尺度最适宜表征农业干旱的SPEI时间尺度为SPEI-6；（2）基于SPEI-6表征的全省农业干旱在1960—2014年呈不显著减小趋势，中度及以上干旱的发生频率为14.4%，重度及以上干旱的发生频率为4.9%；（3）在季节分布上，中度及以上农业干旱在冬季发生频率最高，其次为秋季；重度及以上农业干旱亦在冬季发生频率最高，其次为春季；（4）在年代际变化上，农业干旱的发生频率在1960s最高，而后持续降低，1990s达到最低值，2000s又快速升高。

Standard Precipitation Evapotranspiration Index (SPEI) is one of the most widely used meteorological drought indexes in the global agricultural drought monitoring. Determining the appropriate SPEI time scale is the premise of using SPEI for monitoring agricultural drought. Using the latest national soil moisture reanalysis products as reference, this paper determines the most suitable SPEI time scale for characterizing agricultural drought in Hunan Province based on maximum correlation analysis and then analyzes the spatial and temporal evolution characteristics of agricultural drought in Hunan Province from 1960 to 2014. The results showed that the most suitable timescale of SPEI to characterize agricultural drought is SPEI-6 at the whole province scale. The agricultural drought characterized by SPEI-6 showed an insignificant decrease trend from 1960 to 2014 on the whole province scale. The frequency of moderate and more severe droughts was 14.4% on average, and the frequency of severe and extreme droughts was 4.9% on average. In terms of seasonal distribution, moderate and more severe droughts have the highest frequency in winter, followed by autumn; severe and extreme droughts also have the highest frequency in winter, followed by spring. Regarding to interdecadal variations, the frequency of agricultural drought on the whole province scale was highest in the 1960s and then continued to decrease, reaching the lowest value in 1990s and rapidly increasing in the 2000s.

国家自然科学基金 (NO.51979263)；湖南省重大水利科技专项：湘水科技(【2015】186-12)