| With the rapid advance of urbanization,a large number of ecological and environmental problems have emerged in China.In the context of the increasing urban heat island effect,studying the spatiotemporal changes of thermal environment pattern is of great significance for alleviating urban ecological pressure and promoting human health.Takeing the main city of Xi'an and Xianyang as the typical region of urban thermal environment change and Landsat image data as the main data source,spatiotemporal changes characteristics of summer thermal environment pattern in 2000-2019 have been studied based on standard deviation ellipse,landscape pattern analysis,gradient analysis and other methods.At the same time,using the coupling characteristic model to analyze the dynamic change of the coupling relationship between the construction land expansion and the urban heat island expansion in the urbanization process,and based on the user interest point(POI)big data to explore the influence of human activity factors on the formation of urban heat field on multiple spatial scales,the relative importance of human activity factors and ecological infrastructure on the surface temperature was quantitatively identified.The main conlusions were listed as following:(1)The summer average surface temperature from 2000 to 2019,showed a continuous upward trend.The average surface temperature increased by 7.36?and the area of the urban heat island landscape patch increased by 112.73 km2.After 2006,the phenomenon of urban heat island landscape spreading outward is obvious,forming several new high temperature centers.(2)The distribution pattern of“southeast-northwest”in the spatial distribution direction of urban thermal environment,and the distribution direction and center of]urban island were mainly shifted to the northwest,while the thermal landscape of low-temperature area and medium-temperature area were inclined to the southeas which tend to the river direction.However,The trend of direction and the degree of centripetal force of all kinds of thermal landscape have been weakened.(3)The optimal spatial granularity of spatial pattern analysis of urban thermal environment is 60 m.After analyzing 4 representative landscape indices(LPI?PAFRAC?AI?SHDI),it was found that the overall diversity and information richness of urban thermal landscape were gradually enhanced,and the advantages of thermal landscape in high and sub-high temperature areas were increasing.The spatial pattern of thermal environment had obvious spatial differentiation on landscape level.The thermal landscape in other directions tended to be fragmented and diversified except that the trend of southeast and northwest was not obvious,while the shape of thermal landscape patches in southwest and northeast tended to be complex.(4)There was a very significant positive correlation(R~2>0.7)between surface temperature and the impervious surface index reflecting the level of urbanization.From 2000 to 2019,the construction area of the research area expanded by 491.92km2.In terms of the overall coupling situation,the center of gravity of the construction land and the urban heat island moved to the northwest as a whole,and the two types of gravity centers continued to approach each other,which showing that the overall coupling situation is in the process of continuous strengthening.In terms of the spatial coupling characteristics,the coupling types of construction land expansion and urban heat island expansion were mainly coupled and mildly uncoupled.And the coupling degree of Xianyang is slightly higher than that of Xi'an.(5)There was a very significant positive correlation(R~2>0.15)between surface temperature and POI density.Human activity factor(POI)and ecological infrastructure(NDVI?MNDWI)had a high common interpretation rate(37%-61%)for surface temperature.The overall model with POI density added had a higher interpretation rate than the ecological infrastructure model.POI data can be used as an effective data source to study the urban heat island effect. |
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