| With the development of urbanization,the types of land use have changed and the natural surface has gradually changed into the artificial surface.The expansion of human activities and the change of landscape pattern make the surface temperature in urban areas significantly higher than that in the surrounding areas.Therefore,it is of great significance for urban ecological environment planning to study the correlation between the temporal and spatial evolution trend of urban impervious surface and the distribution of urban thermal environment pattern.In this paper,Fuzhou city is taken as the research area,and the research area is divided into 12 directions on the basis of concentric circles of equal area.At the same time,in order to analyze the change of each area more accurately,the area in each direction is subdivided into 38 rings.Based on the theories of landscape ecology and spatial autocorrelation,this paper analyzes the influence of urban impervious surface spatio-temporal changes on the distribution of thermal environment,and explores the relationship between surface temperature and land use types,human activities and landscape pattern characteristics,providing theoretical basis for urban planning and sustainable development.In this paper,spectral mixture analysis model is used to extract the sub-pixel impervious surface information in the study area,and the surface temperature and impervious surface information are combined to obtain the change of spatial distribution characteristics of urban thermal environment.It can be found that the coverage of impervious surface is also high in areas with higher surface temperature.At the same time,on the basis of concentric circles with equal area,this study combines the hot spot analysis based on surface temperature with vegetation health index to study the changes of urban thermal environment in Fuzhou.The essence of hot spot analysis is to construct a mathematical model by observing the numerical value of each value and its adjacent points,and to describe the hot spot area and cold spot area existing in the whole research area(Ord et al.,2001).That is,the so-called hot spot should be surrounded by other high-value points of surface temperature when it is high.If only a single high-value point of surface temperature is high,it cannot be used as a hot spot in hot spot analysis.Because hot spot analysis does not only depend on the surface temperature,hot spot analysis can more intuitively characterize the influence of land cover change on the surface temperature than other analysis methods in spatial autocorrelation analysis,thus more effectively analyzing the details of urban internal thermal intensity change.On the basis of hot spot analysis,this study is also based on concentric zones of equal area,combining hot spot analysis with vegetation health index to explore the thermal environmental impact of changes in urban landscape pattern.The vegetation health index is weighted and composed of two components,namely,Vegetation Condition Index,VCI and Thermal Condition Index,TCI,and is used to characterize the water content of vegetation.Using hot spot analysis and vegetation health index to study Fuzhou's thermal environment,it is found that:(1)the percentage of impervious surface in hot spots increased from 63.4% in 2000 to 68.3% in 2006,then to 69.7% in2009 and finally to 73.1% in 2016;(2)Heat accumulation expanded obviously to SSE,SSW,WSW and WWW;(3)The number of hot spots in Fuzhou increased from 3 in2000 to 5 in 2016,and the radius of hot spots increased from 1.78,1.93 and 0.95 k m in 2000 to 1.89,2.01,2.10,2.05 and 2.16 k m in 2016.(4)The vegetation coverage of hot spots with high impervious surface coverage decreased obviously in the study area.Although the vegetation health index of hot spots with low impervious surface coverage also decreased with the change of time phase,the deceleration slowed down.(5)Hot spots are regions composed of adjacent high-value points.The vegetation health index per unit area in the region is always lower than that outside the region,and in regions with low vegetation health index,there are often patches of high temperature;However,the further away from the hot spot center,the greater the average vegetation health index. |
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