Study On The Influence Of Trees In The Hot And Humid Area On Urban Thermal Environment And Its Modeling

With the acceleration of urbanization in the world,the outdoor thermal environment has a far-reaching impact on urban micro-climate,air quality,energy consumption,and public health,particularly for the southern China,which has a hot and humid climate,where the heat island effect has a greater impact on the outdoor thermal environment than other regions.Recent research shows that a rational layout of vegetation is an effective means for easing the UHI,which in turn would reduce residential energy consumption and provide better outdoor thermal comfort.Trees,as the most important elements of vegetation,provide multiple microclimate benefits by reducing solar radiation penetration,blocking the exchange of long-wave(infrared)radiation inside urban canyons.However,tree morphology and characteristics are quite different among different tree species,leading to large differences in cooling performance across tree species,particularly across different climatic regions.This study aims to carry out experimental and theoretical analysis of the heat transfer process of common trees species in the hot and humid regions of South China,and propose three-dimensional solar radiation,turbulence and transpiration models of trees.Based on above purpose,this paper focus on the following aspects.First,this study investigates,with field measurements,three physiological indices(leaf transpiration rate,leaf surface temperature,and leaf reflectance)and seven microclimatic parameters(solar radiation,long wave radiation,mean radiant temperature(Tmrt),ground surface temperature,air temperature,relative humidity,and wind speed)characterizing four common tree species in Guangzhou: Ficus microcarpa,Mangifera indica,Michelia alba,and Bauhinia blakeana.Secend,a new three-dimensional model of radiation modification by shade trees is proposed for four common tree species in Guangzhou: Ficus microcarpa,Mangifera indica,Michelia alba and Bauhinia blakeana,and its accuracy was verified with field measurements.Third,using wind tunnel test and real trees,this paper measured the Cd of four common subtropical tree species in Guangzhou.Based on the Cd,a three-dimensional tree model of wind environment modification by trees is proposed,and its accuracy is verified with field measurements and ENVI-met vegetation model.With precise Cd and model,the predictability of the influence of trees on urban wind environments in subtropical areas will be enhanced.At last,field measurement and theoretical calculation were used to obtion the evapotranspiration model which suitable for urban greening in hot and humid areas.We measured the transpiration of the four common trees speicies,and compared the measured data with the results of the SW models.With improved model accuracy of urban trees models,the predictability of the overall numerical framework on surface energy budgets and thermal comfort in urban environments will be enhanced by incorporating the urban trees models in this paper into another urban canopy models.Future development and applications of this numerical model will also help to provide useful guidelines for urban landscape management and sustainable urban planning in terms of,e.g.heat island mitigation.