Study On The Influence Of Urban Form On Thermal Environment

As the development of urbanization,urban heat island effect has become increasingly significant.On account of the lack of effective cooperation between urban climatology and urban planning,urban planning fails to play its “leading” role in mitigating heat island.As the introduction of territorial spatial planning,the importance of “Multi-Disciplinary Cooperation” and “Multi-Plan Integration” has become more apparent.Therefore,the topic of this paper focuses on the research of climate-sensitive planning and design. The albedo is selected as a representative thermal environment-sensitive indicator closely related to urban form for research.The purpose of this paper is to explore the potential of applying this indicator as a breakthrough point to promote the integration and cooperation between territorial spatial planning and urban climatology.Most of the previous researches focus on the albedo of single surface material.However,the researches on the integrated albedo of urban compound built environment are relatively limited.The special solar energy capture effect generated by multiple reflection of solar radiation in the compound built environment is an important factor that lead to the formation of heat island.Moreover,multiple reflection also makes the radiation reflection situation in compound built environment more complicated.Therefore,based on simple investigation and demonstration of the albedo of single surface material and the integrated albedo of a small number of compound built environment,this paper focuses on the research of the integrated albedo of a large number of compound built environment in Chengdu.Based on the integrated albedo perspective,this paper aims at study the influence of urban form on thermal environment.This paper explores the laws of the influence of urban form on integrated albedo and integrated albedo on the thermal environment from different spatial scales and hierarchical scopes,and puts forward the enlightenment of urban form design principles based on integrated albedo regulation.In the basic demonstration investigation,firstly,this paper studies the albedo of single surface material.The field observation method is used to observe the albedo and thermal environment of four typical artificial and natural surface materials including asphalt,brick,lawn and water in the Southwest Jiaotong University campus.The research results show that the albedo of various surface material types is mainly determined by the reflection characteristics of the material itself.And the surface heat island decreases with the increase of the albedo,but the variation law of air heat island with albedo is not obvious.Secondly,in the study of the integrated albedo of the compound built environment,remote sensing inversion and field observation methods are adopted for research.In this part,a small number of local climate zones(LCZ)samples were selected for integrated albedo inversion and thermal environment observation.This part qualitatively discoveries and verifies that the special radiation exchange situation in the compound built environment makes the study of integrated albedo more complicated.The influence of urban form on integrated albedo includes not only the influence of the surface material reflection characteristics,but also the comprehensive influence of the surface cover and geometric structure characteristics.This part initially discovers and demonstrates some influence characteristics: the multiple reflection and obstruction effect on radiation of the buildings and trees vertical surfaces would reduce the integrated albedo.The influence of the integrated albedo on the heat island is easily disturbed by other factors such as building shadow and afforestation.In the formal empirical study,the local climate zones(LCZ)map of Chengdu is constructed based on WUDAPT method,and the integrated albedo and surface temperature data are obtained by remote sensing inversion.Firstly,this paper makes a simple analysis of urban integrated albedo profile.The spatial distribution characteristics of the urban form,integrated albedo and surface temperature are analyzed from the areas within different loops,and the influence characteristics related to the integrated albedo are preliminarily discussed.Secondly,this paper focuses on selecting typical block samples to study the influence laws of integrated albedo.According to the analysis of urban form characteristics in Chengdu,the urban areas of Chengdu are divided into two levels within the third ring road and the central urban area.And 46 LCZ block samples belong to built types and 150 block sample groups belong to built types + land cover types are selected respectively in above two different scopes.After that,this paper explores the influence laws of integrated albedo of different typical LCZ block sample groups in different level scopes through statistical analysis,and compares the differences of the influence laws in different level scopes.The main influence laws can be show as follows:(1)The influence laws of urban form on integrated albedoIn the third ring road,there is a significant negative correlation between building density and integrated albedo,a significant positive correlation between sky view factor and integrated albedo,while no significant correlation between pervious surface fraction / height of roughness elements and integrated albedo.The influence of building density on integrated albedo is greater than that of sky view factor.In the central urban area,there is a significant negative correlation between building density and integrated albedo,a significant positive correlation between pervious surface fraction / sky view factor and integrated albedo.And a significant negative correlation between height of roughness elements and integrated albedo is only found in low-rise types.The correlation degree of pervious surface fraction,sky view factor and building density are higher than that of height of roughness elements.In general,the surface coverage indicators has a stronger influence on the integrated albedo than the geometric structure indicators.On the whole,compared with the scope in the three ring road,the correlations between all urban form indicators and integrated albedo in the central urban area is generally enhanced,and some of the correlations that are not reflected in the three ring road are reflected in the central urban area.No matter in the third ring road or central urban area,both building density and sky view factor have a significant influence on integrated albedo,while the influence of height of roughness elements on integrated albedo is obviously small,and the pervious surface fraction has a significant influence on integrated albedo only in the central urban area.(2)The influence laws of integrated albedo on thermal environment In the third ring road,on account of the small difference of integrated albedo,there is no significant correlation between integrated albedo and its increment and surface heat island.However,in the central urban area,the correlation can be presented more obviously.It indicates that integrated albedo has the potential to alleviate surface heat island to a certain extent.Finally,based on the above influence laws,according to different spatial scales in city,this paper puts forward the enlightenment of urban form design principles and strategies based on integrated albedo regulation in the overall design of the city and the design of the urban district and block respectively.