Urban Summer High Temperature Heterogeneity Research:Landscape Structure And Scale Effects

The acceleration of urbanization has increased the temperature inside the city,forming the urban heat island effect,causing the temperature in the city to be several degrees or even more than ten degrees higher than that in the surrounding countryside,which has brought a great threat to human health and life.The high temperature in summer caused by global climate change has exacerbated this problem.Prolonged high temperature can easily lead to heat stroke and other heat diseases,and even lead to death.Since people’s activities and trips in open spaces are mainly concentrated near the ground,the temperature near the ground has a great impact on people’s life and health.However,at present,there is still a lack of urban thermal mitigation and control measures at a fine scale near the ground,and the temperature difference between different regions within the city may be as large as the temperature difference between urban and rural areas.It is more beneficial to study the impact of different urban landscape types on temperature.variability.Therefore,this study aims to explore the scale effect of landscape elements and near-surface air temperature in summer hot cities.In this paper,11 transects of different landscape structures including water bodies in Changsha,a large city in south-central China,were selected to explore the scale effect of landscape elements regulating near-surface air temperature at different scales(10m,30m,60m,and 90m).First,through the hand-held measurement system based on the STM32 development board,field measurements were carried out during the hottest period of summer,and the measurements included factors such as temperature and wind speed.Secondly,the objectoriented land use classification method was used to classify the transect landscape,and the landscape coverage rate in the buffer zone of different scales was calculated,and the generalized additive model was used to analyze the relationship between landscape elements and near-surface air temperature.The results show:(1)Canopy coverage,impermeable surface coverage,and wind speed have significant effects on air temperature at all scales(10m,30m,60m,and 90m),and the interaction between the three is significant.Among them,the canopy coverage rate has a nonlinear effect on temperature,and the inflection point of the relationship with temperature appears between 25%and 37%.On the scale of 10m and 30m radius,the temperature drops faster when the canopy coverage rate exceeds 37%.The nonlinearity of the 90m radius scale is more obvious,and the temperature drops rapidly when the canopy coverage exceeds 35%.The impermeable surface coverage rate increases from 0 to 100%,and the temperature can be increased by 0.5℃,0.7℃,0.9℃,and 1.7℃ on the scales of 10m,30m,60m,and 90m radii.The 60m radius is nonlinear,and the 90m radius is impermeable.The nonlinear effect on temperature is the most obvious,and the temperature rises faster when the impermeable surface coverage exceeds 50%.(2)When the radius is less than 10m,there is no significant correlation between the surrounding water body coverage and temperature.On the 30m radius scale,the surrounding water body coverage has a slight linear negative correlation with temperature.On the 60m and 90m radius scales,the surrounding water body has a more obvious control effect on temperature,and has a nonlinear effect.When the surrounding water body coverage is close to 100%,the cooling effect can reach 3.4℃,which is smaller than the cooling effect of the canopy at the same scale and the same ratio.,the cooling efficiency is the highest when the surrounding water coverage is 0-50%.(3)On a small scale,the wind speed has a significant impact on the air temperature near the surface,and the wind speed above 5m/s can reduce the temperature by 2℃.The temperature of most shaded places is lower than that of no shaded places,and the median temperature of sample points without shade is the highest,followed by cloudy conditions,and the median temperature of shaded places such as canopy or buildings lowest.The open waterside without shade,the ground cover is impermeable surface or low plants,and the temperature of the sample point exposed to the sun is too high,resulting in a positive correlation between the water body coverage and the temperature.There was no significant relationship between sparse arbor and shrub coverage and temperature,but arbor community,all arbor and shrub coverage,and canopy coverage were significantly negatively correlated with temperature at all scales.