利用中国北方1951~1999年年降水量和年蒸发量资料,计算了干燥度指数 (D), 并据此将中国划分为干旱区 (D(0.20)、半干旱区(0.20~0.50)和湿润区 (D(0.50))。近50a中国干湿气候波动显著,区域差异大：50a波动幅度东北区为20~400 km,华北区为40~400 km,西北东部为30~350 km,西南区为40~370 km。以80年代为界,在20世纪80年代以前(包括80年代),西南区气候具有显著变湿趋势;西北东部稍变湿;华北区和东北区具有变干趋势,且华北区变干程度比东北区严重。进入90年代,西南区和西北东部气候有变干迹象,华北区西部气候的干旱程度有所增加,华北区东部有所减弱,东北区气候进一步变湿。半干旱区是湿润区与干旱区之间的过渡区,是中国季风的边缘地带,也是环境变化的敏感区。20世纪60~70年代中国 (北方)干湿气候存在一次突变,由较湿润变为干旱。50年来干湿气候界线呈现出整体移动和东西、南北相异波动的特征。当干湿气候界线同时向西或向北移动时,中国北方气候就变的相对湿润;当同时向东或向南移动时,北方气候就变的相对干旱;当干湿气候界线东西、南北相异移动时,北方气候的干旱程度就介于二者之间。

Based on the annual mean precipitation and evaporation data of 295 stations covering 1951-1999, the aridity index is calculated in this paper. The climatic regions in China are classified into three types, namely, arid region, semi-arid region and humid region. The number 0.20 (D) is the boundary between arid and semi-arid regions and 0.50 (D) is the boundary between semi-arid and humid climate regions. Dry and wet climate in China fluctuates markedly and differentiates greatly in each region in recent 50 years. The fluctuation amplitude is 20-400 km in Northeast China, 40-400 km in North China, 30-350 km in the eastern part of Northwest China and 40-370 km in Southwest China in recent 40 years. Before the 1980s (including 1980), climatic trend was dry in Northeast and North China, wet in the eastern part of the Northwest and very wet in the Southwest. In the 1990s dry signs appeared in the Southwest, the eastern part of Northwest China and North China. During the 1960s and 1970s dry and wet climates in China had single mutation changing wetness into drought. Moreover, drought shows an increasing trend. Dryly and wetly climatic boundary shows the fluctuation characteristics of the whole movement and the different fluctuations in East, West, South and North directions. The fluctuation of climatic boundary and the dry and wet variations of climate have 10 distinctive inter-annual features. It was drier in the 1950s, 1970s and 1990s in Southwest China, the eastern part of Northwest China (except Hexi region) and the first region in North China. It was wetter in the 1960s and 1980s.