Study On The Influence Of Ecological Land In Chongqing's Main Urban Area On Urban Thermal Environment

The urban heat island effect is one of the most significant features of urban microclimate in the process of urbanization.The good or bad state of urban thermal en-vironment is one of the important indicators to measure the urban ecological environ-ment.It is directly related to the quality of urban human settlements and the health of residents.As China's economic development and urbanization level continue to increase,urban ecosystems are under increasing pressure.Urban ecological land is greatly re-duced.Instead,urban construction land consisting of reinforced concrete and asphalt is added.And a large number of artificial The heat enters the urban air,causing the accu-mulation of heat in the city,making the urban thermal environment worse and worse,affecting the physical and mental health of urban residents and seriously reducing peo-ple's quality of life.As one of the“four major stoves”,Chongqing is the youngest mu-nicipality directly under the central government in China.At the same time,it is located at the strategic point of the“Belt and Road”and the Yangtze River Economic Belt.The urban heat island effect caused by rapid urbanization is becoming more and more sig-nificant.Accurately grasping the development and characteristics of the urban heat is-land effect in the main urban area of Chongqing,and in-depth discussion of the cooling mechanism of urban ecological land use is of great significance for improving the ther-mal environment of the main urban area of Chongqing.This paper takes the main urban area within the Chongqing Ring Expressway as the research area,based on the Landsat series remote sensing images in the summer of2000,2008 and 2016 for land use classification and surface temperature inversion,and further uses high-resolution remote sensing images for typical waters,woodlands and City park extraction.The superposition analysis,spatial analysis and statistical regres-sion analysis are used to explore the spatial and temporal changes of land use/cover,urban heat island effect in the study area and the thermal environment characteristics of ecological land and the impact on the surrounding thermal environment.The main findings are as follows:(1)From 2000 to 2016,the land use/cover change in the study area was severe,and the urban heat island effect became more and more significant.The construction land and other land areas in the study area increased significantly,increasing by 422.86 km~2and 126.96 km~2 respectively.The area of cultivated land and forest land decreased by517.95 km~2 and 54.45 km~2,respectively,and the grassland and water area increased slightly.The lowest surface temperature in the study area increased from 17.33?in2000 to 23.21?in 2016;the average surface temperature increased from 33.87?to38.41?;the maximum temperature increased from 59.69?to 65.59?;the heat is-land distribution area increased from 184.20 km~2 to 368.39km~2.The heat island distri-bution area is highly consistent with the concentrated distribution area of construction land,and the cold island distribution area is consistent with the concentrated distribution area of forest land and water area,indicating that the increase of construction land is one of the main causes of urban heat island effect.Forest land and water area have Good cooling effect.(2)The woodland and waters have obvious cooling effects,but have different cooling mechanisms.The cooling effect of the waters is better than that of the forests.With the intensification of the urban heat island effect,the cooling effect of the forest land is more and more obvious,and the water area has a relatively stable cooling effect.The effective cooling distance of forest land and water area is less than 200m,and the optimal cooling distance of forest land is less than 150m,while the optimal cooling dis-tance of water area is less than 50m.The cooling rate of river within 50m is better than artificial lake.The temperature of the forest land is easy to receive the external factor from the distance of the heat island.The cooling effect is mainly related to its area.The larger the area,the better the cooling effect.The temperature of the water itself is rela-tively stable,mainly affected by its area.The cooling effect is mainly related to the dis-tance from the heat island.The closer the distance to the heat island is,the better the cooling effect is.(3)The combination of water and forestland needs to reach a reasonable proportion to achieve the optimal cooling effect.When the ratio of water area to forest area is0.67-2.33,the best cooling effect can be brought about because the cooling effect of forest land will be covered when the water area ratio exceeds 70%.When the forest area exceeds 60%,the cooling effect of the water area will be Will be converted to insulation.In the case of typical urban parks with roughly the same area,the higher the ratio of water area to forest land,the lower the surface temperature,the better the cooling effect.The urban park with the ratio of water area to forest area greater than 0.67 has lower surface temperature and better cooling effect.