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.