The Temporal and Spatial Distribution of Surface Dry-wet Conditions over Northwestern China in Recent 50 Years
近50年来中国西北地区干湿状况时空分布

Based on the climate data of 77 meteorological stations covering 1958-2001 in northwestern China (the area is within the north of 35oN and west of 105oE in China), and using the integrated Penman formula, the mean potential evapotranspiration (PE) in our study area is calculated. Four patterns of variations of PE and precipitation were detected, showing that the solar radiation and wind speed are two main reasons responsible for the evaporation in the arid area. The aridity index is defined to the ratio of PE and precipitation and is used to describe distribution of the wet-dry conditions in northwestern China. The linear regression trends of the aridity index for the last 50 years show that there are a drying trend in spring and a wetting trend in summer (pronounced only in east Xinjiang and west Gansu) over large parts of the arid areas, and a wetting trend in autumn in most parts of Xinjiang and west Gansu as well as north Qinghai, and in winter, part of the arid area tends to be wetter, and only parts of Xinjiang, Gansu and Inner Mongolia tend to be drier.