Study On The Morphological Samples And Their Thermal Differences Of Chengdu Based On Local Climate Zones

Global warming and urbanization are the two important global environmental problems in twenty-first Century.Urban heat island effect concentrates on the above double effects,and has always been the core focus of the research on the traditional urban thermal environment.In 2016,the national development and Reform Commission and the Ministry of housing issued the action plan for urban adaptation to climate change,which will alleviate the heat island effect as an important goal of urban planning.At present,there are two obstacles in the planning and application of urban climate research results: one is that the traditional urban heat island study mainly uses the "urban and rural dichotomy",which is insufficient to reflect the thermal environment differences within the city;the two is that a large number of urban climate research results are difficult to be directly understood and used by the planners.According to the response ability of urban surface characteristics to thermal environment,a new classification system of surface landscape is constructed and urban heat island is redefined.This paper applies the local climate zoning theory to the downtown area of Chengdu in the hot summer and cold winter zone,verifying the feasibility of the theory.First,at the theoretical level,it collates the basic theories and research methods related to urban thermal environment and urban morphology,summarizes the related achievements of urban morphology and urban thermal environment correlation in urban and block scale,and systematically combs the development process,theoretical framework and relevant needs of local climate regionalization theory.Secondly,the regional climate zoning map of Chengdu Municipal Bureau is constructed on the basis of the theory of local climate zoning in urban scale,and the spatial distribution characteristics of the regional climate zoning of Chengdu Municipal Bureau are analyzed.The results show that there are 14 local climatic zoning types in Chengdu,including 8 built landscape types and 6 natural cover types.The traditional central urban area of Chengdu contains a variety of local climate zoning types.Third,samples of typical samples are sampled to analyze their morphological characteristics,and air temperature data in summer,winter and spring are collected through flow observation,and the rules of thermal environment difference are summarized,and the influencing factors are analyzed.6 typical local climatic zoning types were selected,and the morphological analysis framework was established,including qualitative characteristics and quantitative indicators.The results of thermal environment observation showed that:(1)The difference of thermal environment between different types was not strong during the daytime,and the night showed strong regularity characteristics.(2)there are two aspects of heat difference between different types of night.First,there are significant heat differences among different types.The intensity of heat island in different seasons is as follows: compact high-rise building in urban center,compact middle level building and compact low level building heat island intensity > open middle level building > compact high-rise building on the periphery of city,Open high-rise buildings;two,there are thermal differences among the same types of samples,and urban location,surrounding area shape and artificial heat discharge may have some influence.There is a significant positive correlation between quantitative index building density and heat island intensity.There is a significant negative correlation between sky view factor and water penetration rate and heat island intensity.Fourth,on the basis of the measurement of the thermal environment,the thermal environment characteristics of the typical samples of 6 local climatic zoning types in summer and winter are simulated by ENVI-met.The thermal environment factors include air temperature,wind speed,relative humidity and average radiation temperature.The results show that:(1)air temperature and heat island strength: compact low level buildings in the daytime and open middle level buildings > compact middle and open low level buildings > compact high-rise buildings and open high-rise buildings.The results of the night are in accordance with the measured results.At the same time,the open and low level buildings have lower temperature.2.Wind speed: there was no significant difference among different types.Relative humidity: open type has higher humidity than compact type,and the most obvious performance is in summer.4.Average radiation temperature: compact low rise building > compact high-rise building and compact middle building > open building type.Finally,this paper discusses the possibility of the application of local climate zoning theory in the planning,and puts forward the related thermal environment optimization strategy from two aspects of urban land use layout and control index.