| With the social and economic development,the urban heat island phenomenon is becoming more and more serious,and brings a lot of ecological and environmental problems.Optimizing the spatial pattern of urban greenspace can effectively alleviate the urban heat island effect.The relationship between air temperature and the ratio of green space area has been widely studied,while fewer studies have explored the relationship between air temperature and the spatial configuration of green space(e.g.,patch size and shape)and its scale effect.Exploring the spatial and temporal distribution characteristics of urban air temperature and its relationship with the spatial pattern of green space is the basis for rational planning of urban green space to improve the urban thermal environment.This study is conducted based on hour-by-hour air temperature data from 36 meteorological stations within the third ring of Changsha City in 2020 and land cover classification data decoded from the Gaofen 2 remote sensing satellite.We investigated the effects of land cover area ratio and green space spatial configuration(average patch area(AREA＿MN),patch density(PD),edge density(ED),landscape shape index(LSI),and mean shape index(SHAPE＿MN)on diurnal air temperature at different scales(30 m to 2000 m buffer)using statistical methods such as correlation analysis,regression analysis,and variance decomposition.Theoretically,we found that(1)Changsha city has obvious spatial heterogeneity in thermal environment and spatial pattern of green space.The fragmentation of urban green space is serious and more obvious at small scales.In summer,the maximum temperature difference of 36 sites during the day can reach 1.73℃,and the maximum temperature difference of 36 sites at night can reach 2.94℃.In winter,the maximum temperature difference of 36 sites during the day can reach 1.85℃,and the maximum temperature difference of 36 sites at night can reach 3.34℃,and the standard deviation of night air temperature was greater than that of day air temperature.(2)The proportion of green area has a highly significant negative correlation with air temperature and is scale-dependent.The correlation between the proportion of green area and air temperature fluctuates with increasing scale and is higher during the day than at night.The larger the green area,the more aggregated the patches and the simpler the shape,the stronger the cooling.(3)The spatial pattern of greenspace explains59% of the air temperature variation among 36 sites during the summer daytime,52% of the air temperature variation among 36 sites during the summer nighttime,and 43% of the air temperature variation among 36 sites during the winter daytime as well as nighttime.The spatial pattern of greenspace has a scale effect on air temperature.The correlation between the green space configuration index and daytime air temperature decreases with increasing scale,while the nighttime air temperature shows the opposite trend.At smaller scales,greenspaces explain daytime temperature changes better than nighttime temperature changes,and vice versa.(4)The relative importance of green space ratio versus green space configuration varies with scale and time(summer daytime R50(50-meter buffer zone)and nighttime R100 to R350 range,green space configuration has a greater effect on temperature than green space ratio,while daytime temperatures in the range of R30,R100,R200 and R1500 and nighttime R30,R50 and R400-R2000 green area ratio is greater than green space configuration;in winter the green area ratio is greater than green space configuration in R50 and R100 during daytime and R30-R50 at night,showing opposite results at other scales),the relative importance of green area ratio and green space configuration may depend on the existing spatial pattern of urban green spaces.These results emphasize the scale effect as well as temporal variability of the spatial pattern of urban greenspaces in relation to air temperature.For urban planning practice: the spatial pattern of green space is adjusted with three typical neighborhoods to analyze the effect of spatial pattern of green space on air temperature,and the study finds that only increasing vegetation cover may not necessarily reduce the temperature,and its cooling efficiency also depends on the size of green space as well as spatial configuration.The green space configuration should be reasonably adjusted when the effect of green space configuration on air temperature is more important than the ratio of green space area.In summary,the spatial pattern of urban greenspace has a significant impact on air temperature and changes with time as well as spatial scale.When carrying out landscape planning,we should increase the area of urban greenspace and reasonably plan the spatial configuration of urban greenspace(such as patch density,edge density,etc.),and at the same time,we should pay attention to the law of temporal and spatial changes of the impact of spatial pattern of greenspace on air temperature. |
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