The Influence Of Urbanization Process On The Spatial-temporal Heterogeneity Of Urban Thermal Environment

The expansion of urban area and the change in the types of land use will inevitably lead to the change in urban biophysical parameters,resulting in the variation of urban thermal property,affecting the transformation of urban thermal environment differentiation,which will have great impact on the sustainable development of urban environment and regional economy.Based on Landsat images from 2000 to 2017,this study investigated the spatial expansion trend of built-up areas in Xi'an and Xianyang,respectively,and in-depth analyzed the distribution condition of thermal environment in this study area;along with the increasing of urban area,we also mainly discussed the spatial in-homogeneity of Heat Island Intensity(UHI)and the change in spatial-temporal structure of surface thermal environment;further quantitatively studied the contribution of various surface ecological parameters to Land Surface Temperature(LST),and the interaction between surface ecological pattern and urban thermal environment through building an integrated ecological indicator(IEI)also was quantified at spatial and temporal scales.The important conclusions of this study are as follows:(1)Based on the expansion model of wind rose chart and the LST inversion algorithm developed by Qin,the urban expansion pattern and spatio-temporal distribution of urban thermal environment from 2000 to 2017 can be detected in the study area.During the study period,the pattern of urban development in Xi'an and Xianyang showed "external radiation" and "strip-shaped" development along the Weihe River,respectively;and the overall trend of urban expansion displayed the trend of expanding westward and spreading eastward,respectively,showing the trend of integration of Xi'an and Xianyang.In the context of urbanization,the urban area formed a strong temperature difference contrast with the surrounding environment in Xi'an and Xianyang;and the distribution of thermal environment in different research periods was closely correlated with land-cover types in the study area,and the high temperature environment was mainly distributed in cities,factories and residential lands.(2)The calculation of heat island intensity,analysis of thermal landscape pattern,and cartography of information capacity synthetically displayed the action mechanism of urban expansion on the heat island intensity,distribution of high temperature landscape,and pattern variation of thermal environment.With the rapid expansion of built-up area,the heat island in Xi'an showed a fluctuant trend:increases firstly(2000~2009),and then decreases(2009~2014),then increases(2014~2016),suggesting that the heat island intensity of Xi'an is still significant;and the heterogeneity of landscape pattern in high-temperature areas of Xi'an and Xianyang decreased year by year,but the patch size in high-temperature areas began to increase,and the spatial heterogeneity of thermal environment continued to spread outward,which was consistent with urban expansion trend.(3)The quantitative relationship between surface thermal environment and ecological indicators such as greenness degree(i.e.the Soil Adjusted Vegetation Index,SAVI),moisture degree(i.e.the Normalized Difference Moisture Index,NDMI),dryness fraction(i.e.the Normalized Difference Soil Index,NDSI)and resident aggregation degree(i.e.the Normalized Difference Build-up Index,NDBI)can be reflected by using regression analysis,contribution intensity and Geo-detector.All methods showed that different ecological indicators had various effects on urban thermal environment:Greenness degree and moisture degree were negatively correlated with LST,while dryness degree and resident aggregation degree were positively correlated with LST.Using the principal component analysis method,the constructed IEI can indicate the urban ecological status,and it was negatively correlated with LST as a whole(R~2 values were all greater than 0.75),suggesting that it is very helpful using IEI indicator to study the interaction between urban thermal environment and ecosystem of urban areas.