A Comparative Study Of Atmospheric And Surface Urban Heat Island Effects In China’s Major Cities

With rapid urbanization in China,urban heat island effect is becoming more and more serious,leading to increasing impacts on urban environment and human health.At present,studies of urban heat island effect mainly focused on remotely-sensed radiant land surface temperature.Few studies evaluated atmospheric urban heat island effect,but mainly in a single city or urban agglomeration.The spatial distributions of atmospheric urban heat island effect in different regions and their differences from surface urban heat island effect are unclear.Taking92 major cities in China as an example,the study analyzed the spatial-temporal variations and their drivers of atmospheric urban heat island effect in China from 1960 to 2017 using meteorological and remote sensing observations in combination with multiple data sources like meteorological reanalysis,urban impervious surface area,and statistics.The differences between atmospheric and surface urban heat island effects were then analyzed.The main conclusions are as follows:（1）Most cities in China showed obvious atmospheric urban heat island effect,and the intensity of atmospheric urban heat island varied significantly across cities and regions.The average intensity from 2007 to 2017 was 0.88℃,and the average intensity from 1960 to 2017is 0.89℃.The atmospheric urban heat island differed substantially by the time of day and season,as characterized by higher intensity at night than in the day,in summer than winter during the daytime,and in winter than summer at night.The intensity of atmospheric urban heat island in most cities increased from 1960 to 2009,especially in Northeast China,and the average growth rate of all cities was 0.04℃·（10a）^-1.There is a weakening trend after 2009.（2）The results based on the observation minus reanalysis（OMR）method showed that China’s urban heat island effect had promoted the warming trend in most cities,especially the lowest temperature,reaching 0.26℃·（10a）^-1,with an average contribution rate of 46.7%.The role of atmospheric urban heat island effect in different regions was also different,and atmospheric urban heat island effect contributed the most to the warming in the southeast region.The contribution rate based on urban minus rural（UMR）method was significantly lower than that of OMR method,with an average contribution rate of only 26.8%.Affected by the rapid increase of rural impervious surface ratio,UMR method may underestimate the contribution of atmospheric urban heat island effect to warming in China.（3）The observation results based on remote sensing showed that most cities in China showed obvious surface urban heat island effect.From 2007 to 2017,the average surface urban heat island intensity during the day and night reached 2.04℃and 1.41℃respectively,and there were great differences in different regions.During the day,surface urban heat island intensity（2.61℃）in Southwest China was the strongest,and at night,surface urban heat island（3.19℃）in Northwest China was stronger.The overall performance of surface urban heat island effect was strong in summer and weak in winter,especially during the day.In recent ten years,the intensity of surface urban heat island had increased significantly during the day and night,with an average growth rate of 0.52℃·（10a）^-1and 0.28℃·（10a）^-1 respectively.（4）There were obvious differences between atmospheric and surface urban heat island effect in intensity,spatial distribution,diurnal variation,seasonal variation and interannual variation trend.The intensity of atmospheric urban heat island effect was significantly lower than that of surface urban heat island effect;The atmospheric urban heat island effect is stronger at night than during the day,and the trend of surface urban heat island effect was opposite;The seasonal variation trend of atmospheric urban heat island effect was opposite during the day and night,while the surface urban heat island effect was strong in summer and weak in winter;From the interannual variation trend,the atmospheric urban heat island had weakened in recent years,though the surface urban heat island effect had increased significantly.In addition,it was found that the existing observation data of national meteorological stations had the risk of underestimating the urban heat island effect.The results of this paper confirmed the great temporal and spatial heterogeneity of atmospheric urban heat island effect in China and its difference from the temporal and spatial pattern of surface urban heat island effect,and emphasized the importance of carrying out multi method integration research on a large scale,so as to comprehensively grasp the evolution law of urban heat island effect.However,there were still some problems,such as the lack of representativeness of urban and rural meteorological observation stations,climate reanalysis and limited accuracy of satellite observation data.In the future,it is necessary to strengthen the research on the high-density observation and driving mechanism of atmospheric urban heat island effect.