The Influence Of Urban Tree-lined Street Structure And Tree Canopy Spacing On Pedestrian Thermal Comfort

Due to global warming and accelerated urbanization,the air temperature centered on cities has increased significantly,forming urban heat islands.This phenomenon undoubtedly has a negative impact on the quality of life of urban residents.As the basic unit of outdoor space for urban residents,urban boulevards are closely related to urban residents on urban roads.Street trees,as one of the most important greening elements in the boulevard,greatly affect the urban thermal environment.In this paper,the method of actual measurement and simulation is used to study the comprehensive effects of the three elements of tree-lined street orientation,aspect ratio,and canopy spacing on the summer thermal environment and thermal comfort of tree-lined streets,and propose strategies to improve the microclimate thermal comfort of tree-lined streets.research shows:(1)The orientation and aspect ratio of tree-lined streets have a significant impact on street microclimate;actual measurement and simulation show that the east-west orientation of tree-lined streets is the key to the planning and design of street microclimate suitability in summer.Secondly,in shallow canyons with tree-lined streets(H/W=0.6),the demand for shade from trees is higher,while casting shadows in deep canyons(H/W=1.1)provides additional significant shading benefits and helps To improve the thermal conditions during the summer day.Therefore,the shallow canyon(H/W=0.6)of the tree-lined streets is also the focus of the reasonable design and planning of the street microclimate in summer.(2)Actual measurement and simulation show that the distance between adjacent tree canopies has a significant impact on pedestrian thermal comfort.At the same time,the size of the canopy spacing depends entirely on the number of trees and the size of the canopy,which determine the extent of the canopy coverage.The thermal comfort of pedestrians is determined by the thermal comfort evaluation index PMV.Studies have shown that the reduction of the thermal comfort evaluation index PMV will increase with the decrease of the canopy distance(that is,the coverage of the canopy is high).This kind of humanbiometeorological thermal pressure is relieved in the shallow street canyon(H/ W=0.6)is more significant than the deep canyon(H/W=1.1).(3)ENVI-met4.0 simulation shows that 10 trees in shallow canyon(H/W=0.6)and 8trees in deep canyon(H/W=1.1),and 12 trees in shallow canyon(H/W=0.6)The thermal comfort evaluation index PMV obtained from the regular planting effect of 10 trees in the deep canyon(H/W=1.1)is the same;this proves that based on the same thermal comfort conditions for pedestrians,the deep canyon can save cost and budget.Reasonably reduce the number of trees to achieve a thermal comfort effect similar to a shallow canyon.(4)The simulation of ENVI-met4.0 shows that in the study of control variables,compared with the number of trees,the size of the canopy has the most obvious impact on the thermal comfort of pedestrians between the canopy.Therefore,when considering the thermal comfort of pedestrians in summer,especially the planning of shallow canyons(H/W=0.6)for future boulevards,choose trees with larger crowns,reduce the canopy spacing,and increase the canopy coverage(that is,the crown coverage rate is high).)To improve the thermal comfort of pedestrians on the boulevard.(5)The canopy coverage area increases as the distance between two adjacent canopies decreases,and the thermal comfort evaluation index PMV decreases with the increase in the canopy coverage area;therefore,as the distance between the canopies in the tree-lined road decreases Improve the thermal comfort of pedestrians in the boulevard in summer.