中文摘要：

利用1951-2011年中国756个观测站的月降水资料,分析了北方干旱区和半干旱区暖季降水的变化.结果表明干旱区和半干旱区的降水近60年来表现出相反的变化趋势：干旱区的暖季降水整体是增加的,增长速率为0.27 mm/a,而半干旱区的暖季降水整体是减少的,减少速率为0.80 mm/a.存在这样的差异主要是因为两个区域受不同的环流系统所控制,即干旱区为西风控制区,而半干旱区则为季风区.通过对两个区域降水偏多（偏少）年大气环流的合成分析发现,当西风气流加强、位置偏南,黑海、里海和巴尔喀什湖的水汽被输送到我国干旱区,有利于该地区的降水,反之干旱区降水则偏少；而当东亚夏季风较强时,水汽向西能到达甘肃中部（105？E）,向北能到达整个华北和东北地区,因此半干旱区降水偏多,反之半干旱区降水则偏少.

英文摘要：

The warm-season precipitation changes in arid and semi-arid areas over Northern China were ana-lyzed with monthly precipitation data from 756 stations in China from 1951 to 2011. The results indicated that the precipitation of arid and semi-arid areas showed an opposite trend in the recent 60 years. The warm-season precipitation increased overall in arid areas with 0.27 mm/a and decreased in semi-arid areas with 0.80 mm/a. The difference existed mainly because the two regions were controlled by different circulation systems, that is, the arid area by westerlies and semi-arid area by monsoons. A composite analysis of atmospheric circulation in these two areas for years with more （less） precipitation showed that, when westerly flow was strong and was southward, the water vapor of the Black Sea, the Caspian Sea and Lake Balkhash was carried to the arid region, conducive to the precipitation thereof, and vice versa. When the East Asian summer monsoon was strong and the water vapor was going westward to central Gansu （105？E）, and northward to the entire north and northeast China, the precipitation of semi-arid areas increased, and vice versa.