山地城市空间形态的地表热环境效应——基于LCZ的视角

Assessing Land Surface Temperature in the Mountain City with Different Urban Spatial Form Based on Local Climate Zone Scheme

全球气候变暖背景下,城市高温的强度、发生频率、持续时间和覆盖范围屡创新高,热舒适性已成为影响大城市人居环境质量的一个重要因素。以典型山地城市并有"火炉"之称的重庆市渝中区为例,分析城市空间形态指数与地表温度之间的相关性关系及其作用机理,参考Local Climate Zone(LCZ)方案对城市空间形态进行分类,旨在引导改善城市热环境的规划设计与优化调控途径。研究结果表明,容积率、建筑密度、下垫面不透水面率、平均高度4个形态指数与地表温度之间呈显著正相关,天空开阔度与地表温度之间呈显著负相关,迎风面积指数与地表温度之间没有显著的相关性关系。在城市空间形态类型方面,建设用地比自然地表温度更高。紧凑类型比开放类型地表温度更高,并且表现出低层>中层>高层的趋势。因此,在城市规划建设过程中,通过合理的用地布局,将低层空间让位于绿地、水体等自然要素,建筑向竖向高层发展;在相同建设强度的情况下,高层低密度城市形态更有利于缓解城市热岛效应,提高热舒适性。

Under the background of global warming,the intensity,frequency,duration and coverage of high temperature in urban areas are often exceeding the historical records.Thermal environment has become one of the most important factors affecting the quality of human settlements in cities.In a famous mountain city and“stove”city in China,Yuzhong district of Chongqing is a typical high population density urbanized area with high temperature especially in the summer.Taking Yuzhong district as an example,the potential relationships between urban spatial form factors and Land Surface Temperature(LST)were analyzed by Statistical Package for Social Science(SPSS,version 24.0).The LST was retrieved from Landsat8 images.The six urban spatial form factors were calculated through the current vector topographic maps,including Building Density(BD),Impervious Surface Fraction(ISF),Sky View Factor(SVF),Mean Height(MH),Floor Area Ratio(FAR),and Frontal Area Index(FAI).The Local Climate Zones(LCZ)scheme was used to classify the urban spatial form,which aimed to improve urban thermal environment through the urban planning and design.The results show that FAR,BD,ISF and MH have significant positive correlations with LST,and SVF has a significant negative correlation with LST.However,there is no significant correlation between FAI and LST.The study also found that the LSTs in urbanized areas covered with buildings are higher than those without buildings(that covered with vegetation,water,bare soil,etc.).The LSTs in compact spatial form are higher than the LSTs in the open spatial form.Furthermore,the LSTs vary in different compact spatial form,e.g.,the highest is compact low-rise higher form,followed by compact middle-rise form,and the lowest is compact high-rise form.Therefore,the reasonable layouts of land use and buildings should be considered in the process of urban planning and design,by such ways:providing more space for the green areas,water and other natural elements,and the development of high-rise building.High rise and lower density urban form are more effective to mitigate urban heat island effect and improve urban thermal environment.