Study On Analysis Method And Spatial Characteristics Of Surface Thermal Environment In Chinese Cities And Urban Agglomerations

The urban heat island effect has now become one of the major issues affecting the sustainable development of the ecological environment.Selecting the appropriate urban and rural areas and accurately calculating the Surface Urban Heat Island Intensity(SUHII)will help to fully reveal the urban heat island phenomenon.At present,more studies pay attention to the spatial distribution characteristics of the Land Surface Temperature(LST)in the city,bus pay less attention to the LST outside the urban area.In particular,less research will focus on the impact of urban and rural selection methods on the spatial characteristics of urban heat islands.At the urban agglomeration scale,it is not clear whether the SUHII calculated by urban and rural areas will affect the spatial distribution characteristics of the thermal environment of the urban agglomeration.This paper aims to analyze the influence of different urban and rural selection methods on the spatial characteristics of SUHII in urban 32 cities in China.It also analyzes the gradient of rural LST and interprets LST through surface Albedo and Evaportranspiration(ET).At the urban agglomeration scale,the spatial distribution and variation characteristics of the thermal environment of three typical urban agglomerations in China from 2003 to 2017 were analyzed by dividing LST into five thermal-grade patches.The main research contents and conclusions of this paper are as follows:(1)Based on three factors(water body elevation,rural area,urban-rural integration),six urban and rural selection methods were defined to compare the effects of different methods on SUHII results in different cities and regions.Comparison of different methods,the SUHII calculated by these methods that including water bodies and elevations,not limiting the rural areas,and excluding urban-rural fringe will be larger.Estimates of SUHII in 32 cities are affected by different methods differently.In the analysis of four types of humid and dry areas and seven geographical divisions,the conclusions obtained by different methods are different,and different areas are affected by the method.It shows that different methods have an important impact on the analysis of SUHII spatial features.(2)The LST gradient changes in rural areas in different cities are different.According to the trend,32 cities are divided into three categories(five sub-categories).The LST gradient changes in the same city differed during the day and night.Albedo and ET have a significant effect on LST gradient changes,and ET has a slightly higher explanatory power than Albedo.But for most cities,the two have a stronger ability to interpret and have a stronger impact at night than during the day.This study suggests that the selection of the rural reference should be based on areas where the LST is relatively flat and the fluctuations are not large.The area where LST rises is not considered to be true rural areas and should be avoided as rural areas.For cities with declining LST in the administrative area,it is recommended to select a larger range of averages as a reference for the rural areas.(3)The LST of the three urban agglomerations in China is higher in the southeast than in the northwest.The plaques of the Beijing-Tianjin-Hebei urban agglomeration are relatively concentrated,while the Yangtze River Delta and the Pearl River Delta are more fragmented.The 15-year centroid migration trajectory of Beijing-Tianjin-Hebei and Yangtze River Delta has laws,but the Pearl River Delta does not.The LST of the Beijing-Tianjin-Hebei and Yangtze River Delta has a significant increase in the proportion of LST in 15 years.The significant increase in LST in Beijing-Tianjin-Hebei occurred mainly in the higher LST area in 2003.The Yangtze River Delta has significantly increased in each plaque,while the thermal environment in the Pearl River Delta has improved.The significantly lower proportion is higher,mainly in the higher area of LST in 2003.This study directly divides the LST by the thermal level,avoids the interference of defining the urban-rural boundary when calculating SUHII,and reveals the spatial distribution and variation characteristics of the thermal environment of three typical urban agglomerations from another angle.