The Influence Of Street Tree Types On Microclimate Of Back Streets And Alleys In Qingyang District,Chengdu

With the advance of the construction of "park city" in Chengdu,Chengdu has made a unified arrangement for the greening of roads,and formulated an incremental layout plan of street trees in accordance with the principle of "increasing the greening in an all-round way,planting when it should be planted,and planting when it sees a green seam",which has achieved certain results now.But so far,whether the increment of street trees and the selection of tree species meet the requirements of Chengdu municipal environmental conditions and the needs of users,and whether the street greening environment is comfortable or not has not been verified.Therefore,in this paper,all the tree species of 455 roads in Qingyang District of Chengdu were investigated in detail,and the roads were classified according to their width and function,and on this basis,the investigation,analysis and evaluation were carried out.At the same time,this thesis is based on the venture of chengdu 12 back streets of the city centre for micro climate data collection and analysis,summarized by using the method of control variable and a control group of chengdu venture back streets micro climate,the present situation and the existing problems and discusses trees and trees tree type and micro climate parameters.Finally,based on the above conclusions and discussion,the improvement strategies of street microclimate are put forward.The conclusion is as follows:There are 73 species of street tree species in Qingyang District,belonging to 31 families and 58 genera.The main tree species are Lauraceae,Magnoliaceae,Moraceae and Legume.The average tree height is high and the average DBH is normal.The overall growth state of street trees is good,but it still needs to be maintained frequently.The unbalanced structure of tree species in Qingyang area is reflected in the insufficient development and utilization of native tree species and the insignificant seasonal changes,so the structure of street tree should be further optimized.Chengdu venture back streets of micro climate environment more comfortable,the four seasons of average temperature between 11.0 ? to 29.7 ?,are in a subtropical climate zone,thermal comfort of human body acceptable range,average wind speed 0.17 m/s to 0.47 m/s,fall within the scope of residents' activity is comfortable wind speed,relative humidity from 53.1% to 67.3%,also maintain outside the body feel moderate range.Through the analysis of the data of air temperature,relative humidity,solar radiation and wind speed of the control group in the back streets and open areas,it is found that the street trees in the back streets and lanes have certain influence on the above microclimate parameters.Street trees have a cooling and dampening effect on back streets in spring,a cooling and dampening effect in summer,and an increasing temperature and dampening effect in autumn and winter.The leaf area index(LAI)of the back alleys planted with evergreen trees in four seasons was slightly higher than that of the deciduous trees,while the air temperature,relative humidity,solar radiation and wind speed were all lower than that of the back alleys planted with deciduous trees,and only the relative humidity value was higher than that of the deciduous trees.Through data comparison,it can be seen that evergreen trees have better cooling effect on air temperature and relative humidity than deciduous trees,as well as stronger weakening degree on solar radiation and wind speed.Since the microclimate environment of back streets and alleys in Qingyang District of Chengdu City most needs to be optimized and improved in summer and winter,based on the consideration of reducing temperature and humidity in summer and increasing temperature and solar radiation in winter,the following strategies are proposed for the reconstruction of urban streets: 1)provide shading.According to the site environment,street trees of different tree types are planted,and movable sunshade and sunshade are set.Arcade building system is selected in new commercial blocks.2)adjust ventilation.In a relatively open environment with less shelter,rows of street trees can be planted to form an avenue,or a plant gallery can be built.3)Pavement design.The permeable pavement that can consider light color gives birth to and ground cover plant are united in union,while draining water drops in temperature,also reduce the damp feeling that the humidity after rain increases abruptly as far as possible to bring about.The research of this paper is helpful for the construction of Chengdu park city and provides new ideas and scientific support for the construction of more comfortable green space in back streets and alleys.In addition,the list of street tree resources,analysis of street tree structure and analysis of street tree living structure in Qingyang District of Chengdu City established in this paper provide theoretical and reference basis for the selection,application,introduction and configuration of street tree in the future.