| The urban heat island(UHI)effect refers to a high-temperature phenomenon in which the temperature of a city center is higher than the temperature in the surrounding suburbs or rural areas.The appearance of urban heat islands comes from the rapid development of urbanization.In recent years,the speed of urbanization in Wuhan is amazing.Under the background of rapid urbanization,a series of contradictions and challenges also follow.On the one hand,with the speeding up of urbanization,the problem of UHI is becoming more and more serious.Wuhan is faced with many ecological destruction and environmental pollution problems.The adverse urban thermal environment will also seriously affect human health and quality of life.Therefore,it is of great practical significance to study the thermal environment of Wuhan for the current urban development and future planning.On the other hand,the spatial development of urban areas in China tends to be polycentric day by day,and the pattern of urban heat island has also changed.In the Master Plan of Wuhan City(2017-2035),Wuhan basically presents a polycentric city pattern consisting of main city,new city,3 sub-cities and 3 clusters.However,it is a difficult problem to analyze urban spatial form and urban thermal environment changes in detail for polycentric cities.In order to refine the analysis of urban morphology and urban thermal environment changes from the perspective of polycentricity,the spatio-temporal fusion technology was used to obtain the long-term fine-scaled summer mean land surface temperature data of Wuhan.Based on impervious surface data,morphological polycentricity of Wuhan were extracted by kernel density analysis.This study aims to explore the spatio-temporal evolution of polycentricity in Wuhan,and then analyze the spatio-temporal variation of UHI in typical centers and the influence of driving factors during 2000-2020.The main research contents are as follows:(1)Extraction of polycentricity and analysis of spatio-temporal evolution of its formCombined with Landsat data,linear spectral mixed decomposition method was used to decompose the mixed pixels to extract the impervious surface abundance.Based on the impervious surface data,the impervious surface area with high density was extracted from the perspective of spatial morphology as the centers of Wuhan,and the spatio-temporal evolution of urban polycentric area was analyzed from 2000 to 2020.The results show that the number of centers gradually increases from 5 in2000 to 16 in 2020,and the change process can be roughly divided into five stages.In space,they are mainly distributed in the main urban area and the areas outside the third ring road which include the industrial areas and economic and technological development zones.(2)Analysis of spatio-temporal patterns and driving factors of polycentric urban heat islandLand surface temperature retrieval method based on emissivity and Spatial and Temporal Non-Local Filter-based Fusion Model(STNLFFM)were used,combined with MODIS,Landsat5 TM,Landsat7 ETM+,Landsat8 OLI/TIRS image data,to obtain the Landsat-like summer mean land surface temperatures from 2000 to 2020 in Wuhan.Based on these data,the outer envelopment surface of the urban center is taken as the urban area,and the area outside the urban area is taken as the rural area(water bodies are excluded in all the above areas),and the urban heat island intensity(UHII)is the land surface temperature of the urban minus the mean land surface temperature of the rural.The interannual variation and difference of UHII from 2000 to 2020 were quantitatively analyzed in typical centers.At the same time,the high-temperature areas after LST classification were extracted for kernel density analysis to obtain the high-temperature center and analyze the spatial correlation between Wuhan morphological center and high-temperature heat island.Finally,combined with WI,NDBI and NDVI,linear regression analysis was conducted on the driving factors of LST in the typical central area to explore of the heterogeneity of the influence of driving factors in different centers. |
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