Studies On Summer Cooling Effect Of Outdoor Green Space In Old Districts Of Wuhan Based On Microclimate Model

Urban greening is an effective measure to mitigate urban thermal effects and enhance human outdoor thermal comfort.According to previously studies,large green area ratio and green coverage ratio are required to effectively improve the thermal environment,however,methods related to those conclusions are not applicable to the old neighborhoods with limited open space.In this study,we investigate and discuss the cooling effect of different greenery planting scenarios in old neighborhoods for the limited space between buildings in old neighborhoods using ENVI-met microclimate simulation,and propose cooling planting recommendations for old neighborhoods in Wuhan in summer.In this study,firstly,the feasibility of ENVI_met simulation method was verified,and the green space environment of old neighborhoods in summer was selected for site meteorological measurements and model verification to verify the accuracy of the model in simulating the green space scenario of old neighborhoods in Wuhan city in summer;secondly,the typical building layout of old neighborhoods and the typical planting model of residential areas in Wuhan city were extracted to provide the physical space environment substrate and standard planting model for the simulation study Third,to study the effect of vertical greening layout and vertical greening plant species on the cooling effect in the low-level high-density old neighborhoods;fourth,to study the effect of mono planting form and composite planting form on the cooling effect in the multistory high-density old neighborhoods,based on the basic classification criteria of planting structure Finally,based on the results of the analysis,we propose recommendations for green space renovation in the old neighborhoods of Wuhan.The main research conclusions of this study are as follows:(1)Vertical greening has the best cooling effect on low-rise high-density determinants.When the LAI value of vertical greening plants reaches 4.0,full-covered planting on the north and south sides can achieve the best cooling effect in all scenarios.is 0.7℃.The cooling capabilities of other scenarios are all within 0.6℃.Among all the simulation schemes of vertical greening rate and vertical greening orientation,the north-south full pavement greening scheme,the cooling performance of GFR=40%or 45%is the best.(2)The overall cooling effect of compound planting is better than that of mono planting,and compound planting of large shrubs is better than compound planting of hedge shrubs.The best cooling effect occurs in the situation where the top-covered tree layout is compounded to maximize the planting of large shrubs,which can reach 1.4℃.Before the green plot ratio reaches 0.8,starting from 0.5,every time the green product rate increases by 0.1,the cooling effect will increase by 0.1℃.However,when the green plot ratio is greater than 0.8,the green plot ratio and the cooling trend no longer have a linear relationship.Under the same cooling capacity,a variety of different green plot ratio patterns appear,that is,when the top covering tree layout is the same,the higher green plot ratio(≥1)planted hedgerow shrubs had the same cooling effect as the non-full-covered hedgerow shrubs planted with a green plot ratio of 0.8-1.To achieve the same cooling effect,there are a variety of corresponding greening scenarios,all of which show similar shading ranges.This study not only discusses the cooling performance of vertical greening rate on old neighborhoods,but also investigates the influence of vertical greening species selection on the thermal environment of old neighborhoods.Green plot ratio was also introduced to describe green areas quantitatively,and the connection between the green plot ratio and the greening cooling effect was under disscussion,so as to scientifically and quantitatively guide the renovation and improvement of old neighborhoods from the perspective of green area planning.