近40a中国北方降水量与蒸发量变化

利用我国北方1951-1990年年降水量、年蒸发量、年平均风速和太阳辐射等资料,计算了干燥度指数,并据其将我国划分为干旱区(D<0.20),半干旱区(0.20～0.50),湿润区(D>0.50)。近40a我国半干旱区降水量和蒸发量发生了巨大变化,区域差异显著,年代际特征明显。东北区和华北区降水量具有减少趋势,西北东部和西南区有增加趋势。至于蒸发量的变化,东北区具有增加趋势,华北区、西北东部和西南区有减少趋势。近40a我国干旱半干旱区降水量与蒸发量均在减小,但降水量的减小速度大于蒸发量,气候在变干。我国气候的干湿变化主要取决于降水量的变化。

Variations of Precipitation and Evaporation in North China in Recent 40Years

Based on the annual precipitation, annual mean wind, solar radiation data during 1951 - 1999 of 295 stations, the aridity index was calculated in this paper. According to aridity index, the climatic regions in China were delineated into three types: the arid zone, the semi-arid zone and the humid zone. 0. 20(D) is the boundary between the arid and the semi-arid zones. 0. 50(D) was the boundary between the semi-arid and the humid climate zones. Precipitation and evaporation in semi -arid zone in China have changed greatly in recent 40 years. The differences between each region were substantial and decadal characteristics are noticeable.Precipitation has a decreasing trend in Northeast and North China regions, while, an increasing trend in the eastern part of Northwest and Southwest regions. Evaporation has an increasing trend in Northeast region, while, a decreasing trend in North China and the eastern part of Northwest and Southwest regions. So climate was drying in Northeast China and North China regions, wetting slightly in the eastern Northwest China and wetting greatly in Southwest China region in recent 40 years. Precipitation and evaporation were all reducing in the arid and the semi-arid zones in China in recent 40 years. Moreover, the reduction rate of precipitation was greater than the one of evaporation. So climate in Northern China was turning dry. Dry and wet changes in climate were dependent on the change of the precipitation in China.