| With the continuous advancement of urbanisation,a large number of buildings and impermeable surfaces have been established,causing a series of negative effects on urban ecology,while green space within the city is the key to mitigate the above negative effects while generating certain positive ecological effects,and is the key to reconciling urban development and urban ecology.The article selects the fast-growing city of Hefei in recent decades as the research object.Based on the landsat series of remote sensing image data,the article adopts theories and methods such as literature research method,correlation analysis method and landscape ecology to quantitatively describe the evolution of urban green space in urban expansion.Then,on the basis of the above,the ecological effects of urban green space during the evolution process are studied in various aspects,including carbon sequestration,soil and water conservation,pollutant removal and cooling effect,and the response relationship between urban green space and ecological environment and the mechanism of action are explored.The results of the study are as follows:(1)In the study of the dynamic evolution of green space in the main urban area of Hefei,it includes three aspects from landscape pattern,changes in green space types and vegetation cover.The study is based on the 8-period remote sensing image maps from 1984 to 2020,and uses the supervised classification method to obtain the land use types in the main urban area of Hefei.Firstly,the green space decreased by 516.59km2,which is about 1/2 decrease,and the non-green space increased by 587.08km2,which is 5.3 times increase;meanwhile,the study found that a large amount of green space was converted into construction land,occupying 87.8% of the construction land in2020;the average value of vegetation cover decreased from 0.718 to 0.509,and the high and full vegetation cover area was built up by 222km;from the changes in the landscape pattern index,it can be seen that the landscape patches in the main urban area of Hefei are gradually fragmenting and developing towards heterogeneity,diversifying in shape,and the connectivity between patches is decreasing.In general,as the city expands the green space in the city continues to decrease and fragment,the vegetation coverage decreases,and the green space planning pattern needs urgent improvement.(2)In the study on the estimation of the positive ecological effects of green space and its evolution in the context of urban expansion,the article is based on the remote sensing image map of the main urban area of Hefei,and uses the supervised classification method to decode and classify it with the help of ENVI,ARCGIS,Arc View and other related software to analyse the evolution of green space and its positive ecological effects in four aspects: carbon sequestration,air purification,storm water runoff reduction and cooling effect.The results showed that: the green space in the main urban area of Hefei The results showed that the positive ecological effects of green space in the main urban area of Hefei decreased by a total of RMB 420 million,with carbon sequestration,air pollutant removal and storm water runoff reduction decreasing by RMB 177 million,RMB 5.489 million and RMB 261 million respectively;at the same time,the demand for ecosystem services increased by 700 times,and the change in the value of positive ecological effects in the main urban area of Hefei from high supply-low demand to low supply-low demand.-low demand,to low supply-low demand,to low supply-high demand;in terms of cooling effect,for different seasons,the heat island effect shows summer > autumn > spring > winter.The multiple regression functions constructed for the summer thermal environment,including the coefficients of building occupancy,population density and vegetation cover are 8.372,0.295 and-5.639 respectively,with a constant of 38.555 It can be seen that the supply of positive ecological effects in the main urban area of Hefei is getting lower and lower,but the population is increasing,leading to an increase in demand for ecological values,which represents that the current green space is no longer sufficient to meet the needs of humans in the study area.At the same time,as the city expands,the urban heat island effect increases year by year and the average surface temperature rises,with the increase in population density,building density and the decrease in vegetation cover jointly leading to a rise in ambient temperature and causing the heat island effect.Figure [28] Table [11] Reference [152]... |
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