Abstract:

Based on the Universal Thermal Climate Index (UTCI) from the ERA5-HEAT reanalysis data, China was divided into eight regions by using the rotating empirical orthogonal function method (REOF), namely the Yangtze River Valley (YR), the South China (SC), the North China (NC), the Northwest China (NW), the Northeast China (NE), the Northern of Xinjiang (NJ), the Southern of Xinjiang (SJ), and the Western of China (WC). The variation characteristics of human thermal comfort of the eight regions in China in summer during 1980-2019 were analyzed and the variation reason of UTCI was also explained preliminarily. The results are as follows. In summer, UTCI has been increasing in each region of China, with the largest increase rate in NW where the average UTCI increase rate is 0.053℃/a, and in nighttime, the increase of the minimum UTCI is particularly significant in WC, NW, and SJ, respectively augmented by 112%, 34% and 33%, compared with the increase rate of their maximum UTCI. With the increase of UTCI, the days of strong heat stress and the frequency of the events of strong heat stress for lasting in most areas, have been rising in summer, except for WC. The area with the largest increase rate is NC, with the increase rate of 1.7 days per decade and 2.4 times per decade, respectively. From the analysis of influencing factors, it is found that the rise of UTCI in summer of China is caused by the increase of air temperature, dew point temperature and radiation temperature and the decrease of wind speed. Among the four climatic factors, air temperature is the main climatic factor for the rise of UTCI in China, which the average contribution rate is 49%, and except for SC and WC, radiation is the second largest factor in most areas, while the contribution of other climate factors mainly depended on the variable trend of each region in China.

Key words: Universal Thermal Climate Index (UTCI), Human thermal comfort, Thermal discomfort