Spatiotemporal variations in monthly relative humidity in China based on observations and CMIP5 models

Abstract

The variation trends in surface relative humidity (RH) are analyzed from 1961 to 2015 in China and its eight subregions based on monthly mean surface RH data from 2,474 stations provided by the National Meteorological Information Center of China (NMIC). The annual mean surface RH is 59% in China, with a clear maximum and minimum in South China (SC, 80%) and over the Tibetan Plateau (TP, 45%). From 1961 to 2002, the regional RH shows increasing trends in most regions of China, but a particularly sharp reduction in RH is evident since 2003 in each subregion and throughout China, leading to a decreasing RH in China from 1961 to 2015. The decline is larger in East China (EC, −0.58% decade−1) and SC (−0.59% decade−1) than that in the West of Northwest China (WNC, −0.11% decade−1) and North China (NC, −0.05% decade−1), and the decreasing trend is −0.30% decade−1 throughout all of China. A drier trend has been observed in most regions of China, especially in urban and high-altitude areas, which suggests that the water vapour supply from the ocean is limited, accompanied by weakened monsoons, and the increase in sunshine duration in northwestern China also causes a decrease in surface RH. On the other hand, urbanisation will also lead to local urban dry island effects in some regions with large populations and rapid urbanization. Finally, the RH would decrease more rapidly under the RCP8.5 scenario than under the RCP4.5 scenario because of the asymmetrical increase in vapour pressure and saturation vapour pressure under increasing temperature.