Temporal And Spatial Variation Of The Impervious Surface Area In Major Cities Of Huaihai Economic Zone And Its Thermal Environment Research

With the rapid development of the city,buildings,roads,parking lots and other buildings in the city increase,resulting in the increase of urban impervious surface.The large area increase of impervious surface brings about a series of environmental problems,among which,the change of impervious surface and its thermal environmental effect have attracted much attention.This paper takes the municipal districts of 10 prefecture-level cities in Huaihai Economic Zone as the research object,and uses Landsat series remote sensing data to obtain the change information of urban impervious surface and land surface temperature.Based on the analysis of spatiotemporal variation of urban impervious surface,combined with the characteristics of urban surface temperature change,the characteristics of thermal environmental effect of urban impervious surface change in the study area were discussed.The main conclusions of this study are as follows:(1)In the past two decades,the impervious surface of the prefecture-level cities in the study area has been increasing continuously.The total impervious surface area increased from 1748 km~2 in 1998 to 4591.89 km~2 in 2018,an increase of 2.6 times.The expansion of impervious surface in many cities was higher in 2008-2018 than in1998-2008.The average annual expansion area of urban impervious surface in the study area is between 105.7 km~2 and 178.7 km~2,which belongs to the medium-speed expansion type.Research area are diversified characteristics of the impervious surface expansion mainly envelops type expansion,edge type combined with a jump,radioactive and filling type supplement each other,and the combination of edge expansion and a small amount of fill four expansion mode,there are five cities opaque surface are marginalized and jump a combination of expansion.(2)The change of impervious surface is affected by multiple factors such as nature,economy and policy,but the effects of different factors are often different.Natural factors mainly affect the spatial form and expansion direction of urban impervious surface.In the study area,Among the socio-economic factors,the Pearson coefficient of GDP and impervious surface is 0.827,and the two have a strong correlation.Policy factors affect the expansion direction and spatial structure of impervious surface.(3)From 1998 to 2018,the standard deviation of urban land surface temperature in the study area showed a trend of increasing at first and then decreasing.During1998-2008,the standard deviation increased,the temperature difference between the suburbs increased,and the thermal environment effect was gradually significant.In2008-2018,the standard deviation was reduced to 2.88,the surface temperature in the region gradually moved closer to the mean value,and the urban thermal environmental effects have been alleviated.The high temperature areas in the study area are mainly distributed in the urban core area and the extended area.In the early stage,the high temperature area was dotted and flaky,and the boundary between the high temperature area and the normal temperature area was obvious.By 2018,the range of high temperature areas was expanded,and the boundary between high temperature areas and normal temperature areas in some cities was gradually blurred.The spatial variation of LST can be divided into three modes: point to sheet and then to surface expansion,sheet to surface expansion and surface expansion.(4)There is an obvious correlation between the change of urban thermal environment and the change of urban impervious surface.The results show that the concentrated distribution areas of impervious surface in different periods and different grades are basically consistent with the distribution of the corresponding high temperature areas of surface temperature.The areas with high coverage of impervious surface have high surface temperature.The closer distance to downtown,the surface temperature is higher,the urban thermal environment,the more obvious.However,with the change of urban landscape types,the later high-temperature areas gradually move to the edge of the city center,the temperature difference between the suburbs gradually decreases,and the city is impervious to water.The role of the urban thermal environment is gradually reduced,and the urban thermal environment is alleviated.