Spatial Change of Dry and Wet Climate Boundary in China in the Recent 50 Years

Based on annual precipitation, annual mean wind, and solar radiation data during 1951-1999 of 295 stations, aridity index is calculated in this paper. According to the aridity index, China can be delineated into three climate zones, namely, arid zone, semi-arid zone and humid zone. Aridity index 0.20 is the boundary between arid and semi-arid zone. Aridity index 0.50 is the boundary between semi-arid and humid climate zone. The dry and wet climate boundaries in annual precipitation are compared with the ones of the aridity index in the text. The results show that there is a substantial regional difference for the arid and semi-arid boundary and the semi-arid and humid boundary, and that there is a U type spatial distribution under the circumstances of climate warming and of great spatial difference in precipitation. In the northern part of Northeast China, 250-mm isoline is the boundary between the arid and semi-arid zone and the arid climate zone is consistent with the original zone. 450-mm isoline becomes the boundary between semi-arid and humid. Semi-arid zone retreats westward and its range shortened in northern Northeast China. 300-mm isoline is the boundary between arid and semi-arid zone and 700-mm isoline becomes the boundary between semi-arid zone and humid zone in the southern part of Northeast China, North China, and Hetao District. Arid and semi-arid zone expands southeastward and its range enlarges. In Southwest China and the eastern part of Northwest China to the west of Hetao District, 250-mm isoline is the boundary between arid and semi-arid zone. 500-mm isoline becomes the boundary between semi-arid and humid. Arid and semi-arid climate becomes normal. The spatial change of dry and wet climate boundary in China is depended on the regional difference in precipitation. There is upward trend in precipitation in northern Northeast China. Precipitation has a downward tendency in southern Northeast China, North China and Hetao District. Precipitation is slightly increasing in Southwest China and eastern Northwest China to the west of Hetao District. Precipitation depends on southeast monsoon and southwest monsoon. The former is dependent on the location and the intensity of West Pacific Subtropical High and the latter is caused by Bengalese warm current, westerly circulation and so on.