中文摘要：

利用1961-2011年观测资料分析了西南地区干季（11月至次年4月）降水的变化特征,发现西南地区干季降水在2000年前后发生了年代际尺度的转折,其前后降水空间分布呈现相反的分布特征,特别是21世纪以来降水显著偏少,干旱加剧,降水量显著减少的区域主要在云南大部及其周边地区。西南干季降水和西太平洋副热带高压的负相关在20世纪90年代后期明显加强,而21世纪以来副热带高压表现出明显的年代际增强,即面积增大、强度增强、西伸脊点位置偏西。西南干季降水与副热带高压关系的增强,以及副热带高压本身的年代际增强,对西南干季降水减少造成显著的影响,是西南干旱加剧的可能原因。

英文摘要：

The variation characteristics of precipitation in the dry season （from November to the following April） in the Southwest of China are investigated by using the observation data from 1961 to 2011. The results indicated that the precipitation during the dry season changed remarkably around 2000. The spatial distribution characteristics of the precipitation before 2000 was distinctively different from the characteristics after 2000. The rain was much less than normal and drought got worsened in the 21st century. Precipitation in Yunnan and its surrounding areas reduced significantly. The negative correlation between the rain of the dry season in Southwest and the western Pacific subtropical high （WPSH） strengthened rapidly in late 1990s. Meanwhile the feature of WPSH has shown markedly decadal enhancement since the 21st century. Its area has been growing, with intensity enhancing and position being farther western than normal. Enhancement of the relation between the rainfall during the dry season and WPSH and the decadal enhancementof WPSH, both contribute remarkably to the decline of the dry season rainfall, and probably result in the frequent drought in the Southwest of China.