| In recent years,the contradiction between urban development and ecological environment protection has become more and more prominent in our country.How to construct an ecological city has become the primary problem faced by urban construction,as a high generalization of urban ecological environment,urban thermal environment has emerged a lot of problems with the advancement of urbanization,which poses a great threat to the comfort degree of human settlements and the security of ecological environment,and seriously restricts the sustainable development of cities.At present,Kunming is facing the dual pressure on economic construction and environmental construction with the goal of building a national ecological civilization city.Under this background,the characteristics of the spatio-temporal change of the thermal environment in the main urban area of Kunming City are studied,the influence of natural and human factors on quantitative analysis provides scientific reference for improving the comfort degree of human settlements and constructing ecological civilization city in Kunming.Based on the remote sensing images of Landsat5 TM and Landsat8 OLI,the surface temperature of the main urban area of Kunming was retrieved by using the radiative transfer equation method using ENVI5.3 software,the land surface temperature in the main city of Kunming was classified by the standard deviation method with Arcgis 10.2 software.The spatial and temporal variation of thermal environment in Kunming City from 2000 to 2020 was analyzed by using standard deviation ellipse and landscape pattern analysis.Based on digital elevation model(DEM)and point of interest(POI)data,the influence of natural and human factors on urban thermal environment is discussed,the influence of different factors and their interactions on the thermal environment in the main urban area of Kunming was quantitatively identified by using a geographic detector,to construct the spatial layout of urban natural elements,pay attention to the anthropogenic heat emission,and put forward the measures to alleviate the urban heat environment in Kunming.The main conclusions of this paper are as follows:(1)From 2000 to 2020,the average surface temperature in the Kunming metropolitan area increased by 2.27 °c,the minimum surface temperature decreased by 4.57 °C,and the maximum surface temperature decreased by 4.9 °C.The heat island areas in the main urban area of Kunming are mainly distributed in the densely built areas and bare areas of cities and towns such as industry,population,and traffic.There is a trend of transition from extremely low temperature areas to low temperature areas and lower temperature areas,the middle and higher temperature zones are gradually changing into high and very high temperature zones,and the areas of the high temperature zones in each administrative region are expanding.Guandu District is the area where the thermal environment strengthen most significantly.(2)The direction of the thermal environment in the main urban area of Kunming was generally in the direction of “Southeast of northeast”and “Southeast of northwest”,from 2000 to 2020,the gravity center of thermal environment shifted to the northwest,southeast,northwest and northeast direction,the distance shifted 4.98 km,2.79 km,1.54 km and 0.98 km respectively.(3)By analyzing the change characteristics of the four landscape pattern indices(LPI,PAFRAC,COHESION,SHDI),it was found that the thermal landscape dominance of the main urban area of Kunming has a trend of regular,diversified and fragmentary development.The advantage of the thermal landscape in the extreme low temperature,low temperature,middle temperature and extremely high temperature areas was gradually lose,and the advantage of the landscape in the low temperature,high temperature and high temperature areas was enlarged.The shape of the thermal landscape tends to be complex in the high temperature area,and the shape of the other types tends to develop regularly.The main areas of the thermal landscape were the extremely low temperature area,the low temperature area,the middle temperature area,the high temperature area and the high temperature area.(4)The vegetation coverage of the heat island region in the main city of Kunming was relatively low,and the change of the vegetation coverage area was inversely consistent with the change of the heat island region.At the same time,the surface temperature of the water distribution area was characterized by low temperature,the land surface temperature in the area with high elevation and slope was also relatively low.The land surface temperature of grassland,arable land was higher than that of urban and rural land,industrial land and residential land,and the distribution range of building land based on NDBI index was similar to that of middle temperature zone and heat island zone,the active range of social and economic activities was similar to the spatial distribution pattern of heat island in most areas.(5)The urban thermal environment in the main urban area of Kunming was the result of a number of factors,among which vegetation,water,elevation,slope,land to use type and land surface temperature were negatively correlated,there was a positive correlation between land use,socio-economic activities and land surface temperature.Building land,land to use type and vegetation were the dominant factors that lead to the spatial differentiation of land surface temperature in the main urban area of Kunming,water was an important factor,elevation and slope were secondary factors,and social and economic activities were potential influencing factors.The interaction of elevation/slope and building land has the greatest influence on the land surface temperature in the study area. |
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