Effects Of Urban Spatial Structure On Land Surface Thermal Environment In Beijing

Urban heat island(UHI)effect,as a hot topic in urban ecological research,has an important impact on urban environment and residents' health.Urban spatial structure is an important factor affecting the intensity of UHI.Therefore,it is great significance to improve the quality of urban environment and promote sustainable urban development to understand the influence mechanism of urban spatial structure on spatiotemporal heterogeneity of thermal environment.In this paper,the area within Beijing's fifth ring road is taken as the study area.IKONOS high-resolution image is used to extract six types of surface cover information,and the study area is divided into 5116 urban functional zones(UFZ).According to four Landsat8 OLI_TIRS images in 2014,the land surface temperature(LST)of the four seasons in the study area was obtained through inversion to represent the urban thermal environment.In UFZ,a special spatial analysis unit,the urban spatial structure is described from three aspects: surface biophysical parameters,landscape pattern and building form.Distribution index(DI)and Spatial Lorentz curve were used to explore the spatial heterogeneity of UHI.The least squares model(OLS)and geographical weighted regression model(GWR)were constructed to analyze the main factors influencing the heterogeneity of LST in different seasons.The main results are as follows:(1)There is a strong spatial heterogeneity of LST in the study area.The areas with low LST are mainly leisure areas,which are mainly concentrated in the north of the study area.Other UFZs are relatively warm,especially industrial zones,which are mainly distributed in the southeast,the south and the edge of the study area.Temporal heterogeneity is also significant.The spatial heterogeneity of LST in spring is strongest.The high value accumulation area is mainly concentrated in the south of the third ring and fifth ring,while the low value area is concentrated in the north of the third ring and fifth ring.The spatial heterogeneity of autumn is slightly weaker than that of spring,and the distribution of high and low value aggregation areas are similar to that of spring,but the area of the two aggregation areas are smaller than that of spring.The spatial heterogeneity of LST in summer is weaker than that in spring and autumn.The high value accumulation area is mainly concentrated in the south of the third ring and fourth ring,while the low value is mainly concentrated in the south of the fourth ring.In winter,the heterogeneity of LST was the smallest.The heat island concentration area was transferred to the south of the fourth ring and fifth ring,while the low value area was scattered in the north of the fourth ring and fifth ring.(2)The urban spatial structure in the study area also has strong spatial heterogeneity.The NDBI of the industrial zones are the largest,and the built-up area is relatively large,with dense and low buildings.The built-up area of commercial district and high-density residential zone are dominant,and the buildings are high and dense.The built-up area of the public service zone and the government zone is still large,but it is lower than the above three functional areas.The area of NDVI and green space in the leisure area is the largest,with complex and diverse patches and sparse and low buildings.(3)Urban spatial structure can significantly affect the spatial and temporal heterogeneity of the surface thermal environment.In any season,the influence of surface biophysical parameters on the surface thermal environment is strongest.From the perspective of the influence of urban building form,compared with the height and density of buildings,urban building density has a stronger impact on the thermal environment,and the warming intensity in summer is higher than that in other seasons.For example,10% increase in building density,the LST of spring,summer,autumn and winter increases by 0.17,0.20,0.13 and 013? respectively.From the perspective of landscape pattern,the influence of landscape composition on the LST is obviously greater than that of landscape configuration,and the area percentage of built-up area is obviously greater than that of forest land and grassland.(4)In different seasons,the effect of urban spatial structure to LST is certain different.The influence mechanism of LST in spring,summer and autumn is relatively simple,which is mainly caused by surface biophysical parameters,building density and landscape composition index.In winter,the landscape configuration also has a regulating effect on the LST,but the surface biophysical parameters and building density have the greatest influence.(5)Compared with OLS,the GWR can well explain the effect of urban spatial structure to LST in UFZ.LST in UFZ is strongly influenced by surface biophysical parameters and building density,as well as by landscape diversity.In addition,the landscape composition of built-up area and grassland has a great influence on the LST of the industrial zone,while the landscape composition and spatial configuration of forest and grassland can well adjust the LST of the leisure area.The LST of other UFZs are affected by the landscape composition of built-up area and forest land.