The Interdecadal Fluctuation of Dry and Wet Climate Boundaries in China in Recent 50 Years

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.