The Effect Of Greenery Layout And Morphological Differences Of Trees On The Outdoor Thermal Environment In Old Neighborhoods

The Blue Book on Climate Change in China 2022 points out that the warming trend of China’s climate system is further continuing,directly endangering the overall health of urban residents.Research has shown that greening can improve urban underlying surfaces,alleviate urban heat island effects,and improve residents’ physical and mental comfort.This article first reviews literature on the relationship between tree layout and outdoor thermal environment at various scales,as well as related research methods;After conducting research and greening on 20 old residential areas in Xuzhou City,typical residential areas were selected and common tree layouts and tree forms were summarized,resulting in five tree forms for this study;Fifteen simulation schemes were developed by multiplying the tree layout and morphology using ENVI met;The outdoor thermal environment in summer is quantitatively evaluated from air temperature,humidity,mean radiant temperature(MRT)and thermal comfort evaluation index(PMV).The main conclusions of this study include:1.In terms of arbor afforestation layout,the cooling and humidification ability of regular planting and clumped afforestation layout is better than that of natural cluster afforestation layout.The average daily humidification intensity of greenbelt A reached6.60% under the first two afforestation layouts,while the humidification effect of greenbelt A under the natural cluster afforestation layout was 5.63%.The average daily temperature drop of green space D of 2500 m2 can reach 0.76 ℃ under clumping centralized green space layout,and 0.52 ℃ under natural clumping green space layout.In MRT and PMV,green space A and green space C decreased by 0.87 and 1.10,respectively,compared with the original green space.The benefits of natural cluster afforestation layout are not significant.The reason may be that the vegetation is too dense,which is not conducive to ventilation and cannot release a large amount of water vapor,resulting in poor cooling and humidification benefits.2.In terms of tree morphology,spherical and inverted triangle tree crowns have a good regulating effect on outdoor thermal environment,and the average temperature drop of the four green Spaces is generally over 0.5 ℃.The shape of spherical and inverted triangle trees can reduce MRT of 1750 m2 area of green space by 19.70 ℃,and PMV value by 1.10.In the human body perception table,it becomes warmer from heat and improves human comfort level.3.In terms of air temperature,the umbreller-shaped tree form can reduce the temperature of the four green areas within 0.1～0.3 ℃,and the humidification effect is about 1.3 %,which has no significant regulation effect.The reason may be that the leaves are sparse and the canopy is scattered,which cannot better produce plant transpiration and block solar radiation.4.The shape and diameter of the cylindrical and spire trees are consistent,and the leaves overlap in the natural cluster greening layout,thus shielding the radiation,so the ecological benefits are higher than the first two regular tree greening layouts.Based on the research results,the landscape practice of the target residential area is designed,and the previous,middle,and later stages are analyzed and decomposed to promote the development of urban renewal policies in China,providing new ideas and references for the study of outdoor thermal environment at local scales.