| With the acceleration of urbanization,the rapid expansion of urban space,resulting in changes in the properties of the underlying surface,increasing the level of industrialization at the same time produces a large number of artificial heat release,resulting in the continuous deterioration of the urban thermal environment,which has a significant impact on the urban climate,environmental changes and the quality of life of residents,especially leading to a series of ecological and environmental problems,the most obvious of which is the reduction of surface vegetation and the emergence of heat island effect.In recent years,Harbin’s construction has developed rapidly,the urban spatial pattern has changed rapidly,and the regional thermal environment has undergone certain changes,which has also had a greater negative impact on the urban ecological environment.Therefore,a comprehensive and systematic understanding of the temporal and spatial changes of urban thermal environment and its ecological risk level in the process of urban spatial expansion is of great significance for reducing ecological environmental risks and realizing sustainable urban development.Therefore,based on the Landsat remote sensing image data and night lighting data of Harbin from 2000 to 2020,this paper takes nine municipal districts of Harbin as the research object,performs land surface temperature inversion and landscape type classification,and extracts the urban built-up area.Spatial and spatial evolution of urban expansion and thermal environment was studied by spatial econometric and mean-standard deviation methods,the overall coupling situation model and coordination model were used to explore the spatiotemporal coupling characteristics of urban expansion and thermal environment,bivariate spatial autocorrelation was used to analyze the thermal environment response law in the process of urban spatial expansion,and the main influencing factors of urban thermal environment were explored by using geographic detectors.By constructing the CA-Markov thermal environment prediction model,the distribution pattern of urban thermal environment in Harbin in 2026 is predicted,and corresponding management countermeasures are proposed for the future evolution of thermal environment ecological risks in Harbin,and the following conclusions are mainly drawn:(1)From 2000 to 2020,the growth rate of the area of high temperature area in Harbin was 2.78%,which always showed a growth trend;The area of sub-high temperature area,medium high temperature area and sub-low temperature area showed a continuous downward trend.The area of medium and low temperature areas showed an increasing trend;The area of medium temperature zone and low temperature zone first increased,and then remained stable,showing an overall upward trend.In addition to the built-up areas with relatively dense buildings,the high temperature areas are also scattered in the municipal districts and villages and towns with relatively dense buildings;The sub-high temperature area and medium high temperature area are mainly distributed in the open space inside the built-up area and the exposed surface part that is rapidly warmed by solar radiation.The medium temperature zone is mainly distributed in the cultivated land part;The sub-low temperature area and medium and low temperature area are mainly concentrated in the water body and the grassland and woodland around the water body;The low temperature zone is mainly concentrated in mountainous woodlands with lush vegetation.(2)From 2000 to 2020,the growth of construction land area in Harbin showed an increasing trend,from 280.05km~2 in 2000 to 1571.83km~2 in 2020,with a growth rate of12.7%.The landscape type with the largest decrease in the study area was arable land,which decreased from 7630.94km~2 in 2000 to 6353.7km~2 in 2020,a decrease rate of12.34%.The area of woodland,grassland and unused land remained relatively stable.The area of water bodies is increasing.From the level of patch type,from 2000 to 2020,the proportion of thermal landscape samples in the middle temperature zone was the largest,and the proportion of landscape type and the largest patch index in the heat island area showed an overall increasing trend,indicating that the urbanization process was accelerating and the heat island effect was also increasing.The aggregation index of high temperature area showed a gradual increase trend,indicating that the distribution between plaques in high temperature area was becoming more and more compact.From the landscape level,the patch density and Shannon diversity index of the landscape sample area showed an overall decreasing trend from 2000 to 2020,and the average patch dimension and average patch area showed an overall increasing trend,indicating that the complexity of urban thermal landscape structure composition is decreasing,and the shape of urban thermal landscape pattern is becoming more and more complex.(3)From 2000 to 2020,the scale of built-up area in Harbin continued to expand,from 167.29km~2 to 437.29km~2,of which the built-up area expanded the fastest from 2000to 2008,with an average annual expansion rate of 22.12km~2/year.During the study period,the shape compactness of the built-up area of Harbin was poor,and the fractal dimension of the extended fractal was greater than 1.5,indicating that the city as a whole showed a state of irregular expansion in the past 20 years,and the extension expansion mode was the mainstay.Urban expansion shows certain differentiation characteristics,with rapid expansion in the northwest and due north directions,and slow expansion in other directions.(4)From the perspective of the overall coupling situation,the center of gravity of urban built-up area and urban heat island migrated to the northwest as a whole,and the center of gravity of the two was closest in 2014,showing a more obvious coupling relationship.From the perspective of spatial coordination characteristics,the coordination and enhancement type is mostly the new construction land with rapid urban spatial expansion,and the coordination type of built-up area spatial expansion and urban heat island expansion is mainly coordinated and enhanced type.There was a significant positive correlation between night lighting and surface temperature in the global distribution of space,showing a trend of"first increasing and then gradually decreasing"."H-H(high-high)agglomeration area"is mainly located in urban built-up areas,"L-L(low-low)agglomeration area"is mainly distributed in woodland and water bodies,"L-H(low-high)agglomeration area"is mainly distributed in the periphery of urban built-up area,and"H-L(high-low)agglomeration area"is less distributed.Changes in urban thermal environment are the result of a combination of influencing factors.From 2000 to2020,urban economic development was the dominant factor in the distribution of thermal environment effects in Harbin,and the impact of urban construction intensity on urban thermal environment gradually strengthened.(5)Using CA-Markov model simulation prediction,the distribution of thermal power levels in Harbin in 2026 will still be dominated by medium temperature zone,and the proportion order of each heat island grade area is:medium temperature zone>high temperature zone>sub-high temperature zone>sub-low temperature zone>low temperature zone.From 2000 to 2026,the medium ecological risk areas were mainly distributed in the high temperature area and the medium temperature area,and the average landscape ecological risk decreased from 0.041 to 0.023,showing an overall downward trend;to alleviate the urban heat island effect,measures can be taken from scientific and reasonable urban layout,protection of vegetation and water bodies,low-carbon travel,clean production of enterprises,etc.,to ensure the sustainable development of the urban ecological environment. |
