Comparison Of Cooling Effect Between Urban "Blue And Green Space"

The current process of urbanization has intensified,leading to urban heat island effects and frequent extreme weather events,which have caused damage to the human living environment.Numerous studies have shown that blue-green spaces have a cooling effect,and the rational utilization of urban blue-green spaces is crucial for mitigating urban heat island effects and improving the quality of the human living environment.As the capital of Hunan Province,Changsha City is undergoing rapid urbanization and the issue of urban thermal environment is gradually becoming prominent.It is of great significance to utilize the rich blue and green resources in the region to alleviate the heat island effect.In this context,based on remote sensing images from October 25,2021,April 3,2022,and August 9,2022,this paper uses bluegreen space’s own landscape characteristics,environmental landscape characteristics,and surface inversion temperature as the basic data.Remote sensing technology analysis,landscape pattern index analysis,GIS spatial analysis,statistical analysis,and regression tree model analysis were used to compare the laws of the cooling effect of urban blue-green spaces,the influencing factors and the fit and correlation of the cooling effect,the contribution rate and marginal effect threshold of the influencing factors.The main conclusions of this paper are as follows:(1)The average temperature,cooling intensity,area,and efficiency of the blue space cold island effect are higher than those of the green space.Cold island effects have obvious seasonal differences,with the summer cold island effect being significantly stronger than that in spring and autumn.Blue and green spaces can exert a greater cold island effect during hot seasons.(2)Urban blue spaces have a cooling island effect:①The cooling island effect of blue spaces is influenced by their own landscape features.Area(S)and perimeter-area ratio(P/A)are important influencing factors,while shape index(LSI)has a smaller impact.The larger the blue space,and the lower the edge complexity,the stronger the cooling island effect.②The cooling island effect is also influenced by environmental landscape characteristics.The lower the fragmentation degree and the more complex the landscape patch around the blue space,the stronger the cooling island effect.③The influencing factors have seasonal differences,and the correlation between summer and evaluation indicators is stronger,resulting in a larger cooling island effect.(3)Urban green spaces also have a cooling island effect.①The area and perimeter-area ratio of green spaces play a significant role in the cooling island effect at different levels.②The cooling island effect of green spaces is strongly related to environmental landscape characteristics.The lower the degree of landscape fragmentation,the greater the complexity of shape and landscape heterogeneity,and the higher the degree of aggregation and connectivity,the more favorable it is for the cooling island effect.③The seasonal differences of green spaces are more pronounced,and the correlation between influencing factors and the cooling island effect is more significant during the high-temperature season.(4)There are differences in the contribution rates of factors affecting the urban blue-green space’s cool island effect.①Comprehensive analysis indicates that the cool island effect of urban blue-green space is influenced by its own landscape characteristics and environmental landscape characteristics.Blue spaces are mainly influenced by their own landscape characteristics,especially the blue space area(S)and perimeter-area ratio(P/A).Adjusting the scale and edge complexity of blue spaces plays an important role in enhancing their cool island effect.②Green spaces are more affected by the environmental landscape characteristics,and factors such as the proportion of patch area(PLAND),average patch nearest neighbor distance(ENN_MN),and index of clumping(CLUMPY)are important influencing factors.(5)The factors affecting the cool island effect have different marginal effect thresholds.①After reaching the marginal effect threshold,continuing to change the influencing factors will have a smaller effect on the cool island effect.②Generally speaking,the threshold values for the landscape characteristic factors of blue space are higher.In the summer,the threshold value of the green space area for cooling intensity is around 15 hm2,while the threshold value for blue space is around 40 hm2(6)Recommendations for optimizing the design of urban blue-green spaces:In the planning and design of urban blue-green spaces,it is necessary to fully consider the landscape characteristics and Environmental landscape characteristics of blue-green spaces to maximize their cool island effect.Therefore,the following optimization recommendations are proposed:①Ensure the scale and optimize the design of urban blue spaces;②Consider the threshold effects,individual and collective effects of influencing factors;③Consider the seasonal changes in the influencing factors of the cool island effect when designing blue-green spaces,and blue-green spaces should have a greater cool island effect in summer.