中文摘要：

依据1961-2009年中国区域540个气象站的夏、冬季气温和降水数据，首先采用气候变化趋势转折判别模型（简称PLFIM）分析了中国区域8个分区夏、冬季气温和降水的年代际变化，而后利用PDSI干旱指数研究了夏、冬季极端干旱在年代际尺度上的时空变化特征及其成因。结果表明：1961-2009年中国夏季极端干旱发生率北方大于南方，冬季则为在东部多而在西部少。夏季和冬季极端干旱发生概率在最后一次年代际转折后都呈增加趋势。在区域尺度上，夏季东北、华北和西北地区增加明显，冬季东北、华北、华南、西南地区增加显著。其中，降水在20世纪90年代以前的极端干旱变化中起主导作用，而后由于气候变暖所引起的极端干旱增加趋势逐渐增大，与降水变化的作用相互叠加。

英文摘要：

Temperature and precipitation data from 540 meteorological stations in China from 1961 to 2009, and the piecewise-linear fitting model （PLFIM） was used to analyze the changes in summer and winter temperature and precipitation at the interdecadal timescale. The Palmer drought severity index （PDSI） was chosen to examine the frequency of extreme droughts. Consequently, the interdecadal changes and spatial distribution characteristics of extreme droughts were analyzed for summer and winter. Furthermore, we considered the effect of temperature and precipitation on the occurrence probability of extreme droughts. The results suggest that from 1961 to 2009, extreme droughts were more frequent in northern China than in southern China during summer, whereas they were more frequent in eastern China than in western China during winter. After the last trend change, the occurrence probabilities of extreme summer and winter droughts increased. At the regional scale, the probability of extreme summer droughts increased in Northeast China, North China, and Northwest China, whereas the probability of extreme winter droughts significantly increased in Northeast China, North China, South China, and Southwest China. The analysis of the causes of the variations in theoccurrence probabilities of extreme droughts showed that the precipitation change controlled the trend in the occurrence probability of extreme droughts before the 1990s. Subsequently, climate warming led to an increasing trend in the occurrence probability of extreme droughts, whereas the temperature and precipitation changes controlled the occurrence probability of extreme droughts over China.