A Study of Surface Humidity Changes in China During the Recent 50 Years

This paper analyzes in detail the characteristics of surface humidity changes in China under the background of global warming in the recent 50 years by using the observation data compiled by the National Meteorological Information Center of China. The results reveal that (1) with the increase of temperature, surface saturation specific humidity (qs) shows basically an exponential growth, according to the Clausius- Clapeyron equation. The nationwide average moistening rate in winter is obviously less than the annual average rate and the summer rate. There are some regional differences in qs trends in different regions of China. For example, qs in central and eastern parts of China exhibits a reducing trend in summer, consistent with the weakening trend of temperature in these areas; (2) except parts of South China and Jianghuai Region in eastern China, unanimously increasing trends of annual and winter specific humidity (q) are found in most of China, especially in western China. In summer, except parts of Northeast China, Northwest China, and some areas over the Qinghai-Tibetan Plateau, the decreasing and drying trends are significant in most of China, which is not consistent with the global mean situation; (3) the surface relative humidity (RH) in most of China shows a reducing trend. One of the major reasons for the reduction of RH is that the increasing rates of q are smaller than those of qs. Nonetheless, upward trends of RH in central and eastern China mainly due to the cooling temperature and rising q in these regions are observed in summer, leading to more precipitation. From about 2003 or so, qs has remarkably increased while q has sharply decreased in most parts of China; therefore, RH has reduced to a great extent. This may be closely related to the persistent growth of drought areas in China in the recent 10 years.