Study On The Cooling Effect Of Urban Parks Based On Field Meteorological Observation And Point Cloud Data Obtained By Terrestrial Laser Scanner

Rapid urbanization has changed the land surface and resulted in the temperature difference between city and rural area,which is called urban heat island(UHI).The UHI has caused serious negative impact on living and producing of city residents.As an essential component of the urban natural landscapes,urban green space can mitigate urban heat island effectively.Taking purple mountain forest park and Dr.Sun Yat-sen's botanical garden in Nanjing City as a study areas,we used the HOBO meteorological stations to get micro-meteorological factors such as air temperature,relative humidity and wind speed.We also used the Leica Scanstation 2 to obtain cloud point data of the forest vegetation and accordingly,their green quantity and shade of vegetation at each station were then calculated.Supported by the statistical and correlation analysis,the gradient change characteristics and the factors contributed to the green space cooling effect were analyzed.The results can help us to understand the factors impacting on the green space cooling effect and then can provide practical guidelines for the urban green space planning and design.This thesis was constructed by seven chapters.The first chapter introduced the research background and significance,then reviewed the related research,and finally sketched out the basic framework of this research.The second chapter introduced the selected study area.The third chapter gave a detailed description on the instruments,data capture and the corresponding data processing.The fourth,fifth and the sixth chapter are the main parts of this thesis.The fourth chapter analyzed the gradient changing characteristics of the green space cooling effect.The fifth chapter discovered and analyzed the contribution of vegetation canopy to green space cooling effect at a park scale.The sixth compared the microclimate conditions of the two study areas,and discussed the influence of microclimate characteristics on the green space cooling effect.The seventh chapter systematically summarized the main conclusions and innovations of this research,and put forward the disadvantages and the direction future study would perfect.The results indicated as follows:(1)The characteristic of gradient change in purple forest park showed the results that,during the observation period from July 10th to July 13th,the trend of gradient change was comparatively obvious during the daytime(5:10-19:10)only on July 11th,with the cooling effect decreasing from the center to the edge of the purple mountain.The green quantity and shade of each station were the two most significant factors that could explain this phenomenon,and they had different impact on it at different period of time.Green quantity had a comparatively obvious effect on the temperature reduction during 9:00-18:00.The maximum correlation coefficient between them could up to a value of 0.74(at 9:00).Shade had a comparatively significant effect except 11:00-13:00,with the correlation coefficient around the value of 0.7.However,during the night(19:10-5:10),the trend of gradient change was obvious with the cooling effect increasing from the center to the edge of the purple mountain.It was mainly because of the gradient change of terrain and the microclimate change that result from terrain.(2)Taking Dr.Sun Yat-sen's botanical garden as study area,we selected four woodland of different vegetation structure as investigation spot,to quantitatively study the influence vegetation canopy on the cooling effect.The four spot were Cinnamomum camphora,Metasequoia glyptostroboides,Magnolia grandiflora and a mix-woodland with several different species.The results showed that tree species had different cooling effect due to the size,optical properties and dense degree of their leaves.The temperature reduction decreased gradually from Metasequoia glyptostroboides,Cinnamomum camphora,Magnolia grandiflora and the woodland with several different trees in order,being strong in the daytime(5:00-19:30)and weak during the night(19:30-5:00).Green quantity and shade had important impact on it.Green quantity had a comparatively obvious effect during 8:00-18:00,with the maximum correlation coefficient up to a value of 0.63(at 9:00).Shade had a comparatively significant effect except 11:00-13:00 with the correlation coefficient greater than the value of 0.6.We also introduce LAI(Leaf area index)and SVF(Sky view factor)in this study,to compare the effect with green quantity and shade respectively.Results showed that green quantity and shade could more accurately reflect the impact that vegetation canopy had on the cooling effect.(3)Comparing the microclimate conditions of the two study areas,we analyzed the impact of microclimate factors on the cooling effect.The results demonstrated that the temperature reduction of all the research points showed the increasing trend with the rising of air temperature,solar radiation,and decreasing with rising of relative humidity.The impact of background microclimate factors on cooling effect is comparatively complex.Generally,the cooling effect increased with the rising of air temperature,solar radiation,and decreased with rising of relative humidity.The impact of wind was limited by the study area and temperature.The wind speed showed negative correlation with temperature reduction when the average temperature exceed 36? at 10:00-16:00.