The Variation Characteristics And Projection Of Human Thermal Comfort During Summer In China Based On UTCI

Under the background of global warming,compound events characterized by high temperature occur with higher frequency,stronger intensity and longer duration,which seriously affect social life and threaten human health.Establishing the connection between high temperature weather and human health and studying the variation in human thermal comfort under the background of global warming can not only deepen the understanding of the impact of climate warming on the human living environment,but also provide references for improving urban environment and upgrading urban livability.Based on the universal thermal climate index UTCI in the ERA5-HEAT data set,the variation characteristics of human comfort during summer including June,July and August from 1980 to 2019 in China divided by eight regions were analyzed comparatively,and the reasons for the variation were explained preliminarily.Furthermore,based on the 10 models data provided by CMIP6 and after revised,the UTCI response to global warming up to 1.5?/2.0?/3.0?/4.0?under different scenarios was projected,and the impact of thermal discomfort on population and urban land was evaluated by combining the future population and urban land area data.The results show that:(1)In the past 40 years,UTCI in eight regions of China has rised in different degrees.Among them,the Northwest region has increased fastest,with an average growth rate of0.053°C/a;the thermal discomfort(UTCI?32°C)hours and the frequency of thermal discomfort lasting for more than 3 days increase the fastest in North China,which were 4.2h/a and 2.4times/10a,respectively.The reason for the rise in UTCI is the increase in air temperature,dew point temperature and mean radiant temperature and the decrease in wind speed.Temperature is the dominant factor in the variation of human comfort during summer in China,with an average contribution rate of nearly 49%,and radiation is the second largest climate factor in most regions except for the Southern of China and the Western of China,which indicates the importance of radiation in evaluating human comfort.(2)With the increase of global temperature in the future,the UTCI in northern China will respond faster to global warming than the southern,and the UTCI in the Northwest region will respond fastest,with the increase of 7.07°C when the temperature increases to 4.0°C under the SSP585 scenario.With the rise of UTCI caused by global warming,the possibility of occurring thermal discomfort increases,the area of thermal discomfort expands,and the number of thermal discomfort days increases during summer in China.On average across the country,the probability of occurring thermal discomfort will increase by 38.90%,the thermal discomfort area will expand by 1121.88%,and the days of thermal discomfort will increase by 26.24 days per year when the temperature increases to 4.0°C under the SSP585 scenario.Among them,the days of thermal discomfort will increase more in the Yangtze River Valley and the Southern of China,reaching 45.53 and 37.70 days per year respectively,while the days of thermal discomfort will increase fastest in Northern of China,with a maximum increase of 6.74 times.(3)As the global temperature increase in the future,the population and urban land area exposed to thermal discomfort will also increase.The population and urban land exposure to thermal discomfort in the Yangtze River region will be the most serious area,with 3.28×10~6person·day and 1.60×10~4 km~2·day,respectively,while the exposures to thermal discomfort will increase the most rapidly in the Southern of China,with 3.24 times and 12.39 times,respectively.Climate is the main factor of the increase of population exposure,while the interaction of climate and urban land area is the main factor of the increase of urban land exposure.If the temperature can be controlled within 1.5?,the impacts of the rise of UTCI and thermal discomfort days will be avoided up to 90.51%and 95.49%,respectively,meanwhile 34.28 million people and 1.50 million km~2 urban land area will be avoided from thermal discomfort.