Research On The Change Of Urban Underlying Surface And Its Influence On Thermal Environment

In the past two decades,China has experienced the fastest urbanization process in history.At the same time of rapid economic development,the urban heat island effect has intensified.Urban heat island,which is directly related to the quality of human production and life living environment,leaves profound impacts on urban climate,energy and resource consumption,ecosystem and socio-economic sustainabledevelopment.The change of underlying surface properties is an important driving mechanism of urban heat islands.Studying the spatial and temporal changes of urban underlying surface and its driving mechanism to urban heat islands is of great significance to alleviating urban thermal environment and reducing social and economic losses,and is conducive to improving living environment.Promote the construction of ecological civilization.Based on RS and GIS technology,this paper apply the atmospheric inversion method to analyze the spatial and temporal changes of the urban thermal environment in Chaoyang District of Beijing during the 15 years from 2002 to 2017 using the Landsat remote sensing images from the district in the summer.The obtained land surface temperature was normalized to obtain the distribution of urban heat islands,and the urban-heat-island radio index was used to quantitatively describe the thermal environment changes in Chaoyang District.At the same time,the change of the underlying surface in the Chaoyang District during the 15 years was studied.Firstly,Google's full-color satellite imagery was used to classify the underlying surface coverage type based on the Deeplabv3+network.Then,the normalized vegetation index(NDVI)and the normalized built-up index(NDBI)were calculated based on the Landsat remote sensing images.Then,the single-factor regression analysis of surface temperature-normalized vegetation index(NDVI),surface temperature-normalized built-up index(NDBI)and multiple linear regression analysis of the three were carried out in SPSS.Finally,the influence of urban parks layout in Chaoyang District on urban heat island is studied;and the cooling effect of urban parks at different scales is quantitatively studied.The main conclusions are as follows:(1)During 2002-2017,the land surface temperature in Chaoyang District generally showed an upward trend,and the urban heat island effect increased year by year.The urban heat island center gradually changed from the distribution structure of points,lines and planes in early years to the distribution of complex nested structures in multiple centers.In 2002,the urban-heat-island ratio index was 0.0165;in 2017,it reached 0.1156,which had increased by more than 6 times in 15 years.(2)The change of the underlying surface in Chaoyang District during 2002-2017 was mainly the process of mutual transformation between impervious surface,vegetation and waters.In the past 15 years,the area of impervious surface has decreased by 71.02km2,a decrease of 20.98%.The water area decreased by 2.53km2,a decrease of 24.12%.The total area of vegetation increased by 73.54km2,an increase of 56.57%.The average of the Normalized Vegetation Index(NDVI)increased by about 1.7 times.The average of the Built-up Index(NDBI)increased by 9.63%.(3)The land surface temperature was positively correlated with the NDBI index:every increase of 0.1 in the NDBI index would cause the land surface temperature to rise 0.8-2.4?;negatively correlated with the NDVI index:For every 0.1 increase in the NDVI index,a cooling in the range of 0.4-0.8? will be formed on the land surface.(4)The urban park layout affects the urban heat island effect.The cooling effect of the urban parks and its area relationship can be fitted to a logarithmic function,but the cooling distance does not increase indefinitely as the area increases.The cooling distance of the comprehensive park is within 650m of the vertical direction starting from the green space boundary,and the cooling distance of the community park is within 350m of the vertical starting from the green space boundary.From the perspective of ecological benefits and cooling efficiency,it is recommended that the area of the comprehensive park should not exceed 19 hectares and the community park should not exceed 10 hectares.In this research the urban thermal environment and heat island evolution and the temporal and spatial changes of the underlying surface in Chaoyang District of Beijing were studied in depth.The correlation between vegetation,impervious surface and land surface temperature was quantitatively analyzed,and the change of underlying surface to urban heat island was revealed mechanism.Finally,taking urban parks as an example,the research on the impact of green space pattern on urban heat island is carried out;and the cooling effect of urban parks on different scales is quantitatively analyzed.The results obtained from the study have important guiding significance for urban planning,urban green space construction,economic and ecological sustainable development in Chaoyang District.