| With global urbanization,impervious surfaces are rapidly encroaching on agricultural land,causing qualitative changes to the substrate,leading to urban heat island effect and other ecological and environmental problems,and seriously affecting the quality of life of residents.Urban "blue-green space",as a cold island area in the city,has the function of alleviating urban heat island and reducing the temperature of the surrounding environment.It is important to fully understand and utilize the cooling effect of urban "blue-green space" to alleviate the urban heat environment,improve the living environment and enhance the urban ecological construction.This study takes the central city of Jinan as the main research area,based on Landsat remote sensing images and GF-2 remote sensing image as the main data sources,and uses single window algorithm,linear spectral mixture model and object-oriented classification method to construct six urban surface temperature datasets from 1990 to 2021,urban "blue-green space" coverage datasets,and access to urban park refinement land use types;The spatial analysis was used to analyze the spatial and temporal distribution and landscape pattern evolution of urban thermal environment and urban "blue-green space";statistical regression was used to analyze the cooling effect of urban "blue-green space" on thermal environment through different spatial scales;we selected two types of landscape indices,landscape composition and landscape configuration,to characterize the geometric characteristics of urban parks,and explored the cooling effect of urban park "blue-green space" and its influencing factors.The main findings of this study are as follows.(1)The spatial distribution of "blue-green space" in the study area has not changed significantly in the past 30 years,and the area change is more obvious.Spatially,"blue space" is concentrated in the Yellow River basin,and "green space" is concentrated in the surrounding agricultural land and mountainous areas.The total area of "blue and green space" shows a trend of decrease,as shown by the total area decreasing from 685.47km~2 in 1990 to 578.12km~2 in 2021,with an overall decrease of 107.35km~2.In the past 30 years,the green space within the built-up area tends to be distributed in a regional and decentralized manner,and the area increases from 15.84km~2 in 1990 to 86.42km~2 in 2021.By analyzing the changes of "green space" landscape pattern in the built-up area with the grid,the green space abundance value in the built-up area in the past 30 years shows a pattern of low in the middle and high in the periphery,the green abundance value is higher in the urban expansion area;By comparing the difference of green area under the grid between two adjacent years,the change of green space area in the built-up area in the past 30 years is mainly based on mild increase,with the ratio of 0.42,0.66,0.28,0.71 and 0.58 between different years,respectively.(2)With the accelerated urbanization process,the thermal environment in Jinan has changed significantly in both spatial distribution and temporal changes in the past 30 years.In terms of spatial distribution,the surface temperature of the built-up area in the center of the study area is higher,and the surface temperature of the surrounding mountainous areas as well as agricultural land is relatively lower;in terms of temporal changes,the heat island intensity shows a trend of first strengthening and then weakening,tending to strengthen during 1990 to 2016,with the average surface temperature increasing from 22.84°C to 28.45°C,and tending to weaken during2016 to 2021,with the average surface temperature decreasing from 28.45°C to 26.11°C;the heat island extent expands with the expansion of the city.By normalizing the surface temperature and then analyzing it,the proportion of medium-temperature area in the study area is the highest in each period,accounting for 48.38%,44.93%,27.62%,31.78%,32.35%,and 34.73 %,respectively;the heat island effect in the built-up area tends to alleviate in the last 30 years,as shown by the reduction of the total area of high temperature and higher temperature in the builtup area from 70.75%(1990)to 36.35%(2021).(3)Urban "blue and green spaces" have significant cooling effects on the thermal environment.The differences between the LST of blue space,the average LST of blue-green space,the LST of green space and the average LST of the study area were compared,and the temperature differences were 3.04℃,2.64℃ and 2.24℃ in 2002,for example,and in all other years,the cooling effect is the strongest in the blue space,followed by the blue-green space and finally the green space.the cooling effect of blue-green space is most obvious in 2002(2.64℃),2016(2.32℃)and 2009(2.03℃),followed by significant cooling effect in 2021(1.69℃)and1996(1.29℃),and finally in 1990(0.84℃).Blue-green space,green space and blue space have different cooling effects in different years and at different spatial scales.(a)The correlation between blue-green space at 450 m,900 m and 1200 m spatial scales and the LST in 2002 is the most significant,and when the area share of blue-green space increased by 10%,the surface temperature can be reduced by 0.82℃,0.88℃and 0.91℃ at different spatial scales respectively;(b)The correlation between green space at 450 m,900 m and 1200 m spatial scales and the LST in 2002 is the most significant,and when the area share of green space increases by 10%,the surface temperature can be reduced by 0.82℃,0.88℃ and 0.89℃ at different spatial scales respectively;(c)The correlation between blue space at 450 m,900 m and 1200 m spatial scales and the LST in 2016 is the most significant,and when the area share of blue space increased by 10%,the surface temperature can be reduced by 0.41℃,0.54℃ and 0.57℃ at different spatial scales respectively.(4)Tree Area and water are important components of urban parks,which constitute a small "blue-green space" inside the parks;the surface temperature inside the urban parks is 3.6℃ lower than the average surface temperature of the study area,which has a certain cooling effect,and the average area affecting the cooling of the surrounding environment is 120.68 ha.The park was classified into four categories: regular temperature park,temperature decreasing park,temperature increasing park and other parks by the cooling law of the park on the surrounding environment.The park area,water area proportion and NDVI are the key factors influencing the cooling of the park,among which the park cooling effect is best when the park area is larger than20ha;when the water area proportion in the park increases by 10%,the park cooling intensity can increase by 0.89℃. |
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