高密度城区形态要素对热环境的影响作用——以北京市五环内区域为例

Impact of Urban Morphology Factors on Thermal Environment in High Density Urban Areas:A Case of Beijing within 5th Ring Road

近年来的快速城市化进程导致各大城市的人口规模高速增长以及建设强度迅速提升,催生了大量的高密度城市建成区,极大地改变了城市生态环境,出现了热岛效应等问题。在众多影响城市热环境的因素中,物质空间形态的作用十分显著,对其进行优化设计进而缓解热岛效应被视作具有较大潜力的可行措施,但目前城市形态要素对热环境的影响作用仍不清晰。以典型高密度建成区北京市五环内区域为研究范围,将研究区划分为对应城市街区规模大小的500 m边长网格的基本单元,选取城市规划体系中控制性详细规划对城市形态管控的关键性指标,通过遥感反演解译和空间分析等方法计算各网格内的平均地表温度以及各城市形态相关指标数据,建立OLS以及GWR回归模型,深入剖析建筑密度、容积率、绿地率等指标对城市热环境的作用规律。结果表明,(1)城市形态要素对热环境具有显著影响,建筑密度增加导致地表温度上升,容积率、绿地率的提升引起地表温度下降。(2)各指标对热环境的作用具有空间非稳定性,主要水体周边建筑密度的增温能力最强,且容积率反常地导致增温效应;绿地率在建成区边缘地带产生的降温效果较强。(3)OLS模型对某些指标变量在部分空间区域的热环境作用估计存在偏差,GWR模型可更准确地反映各指标变量对热环境的影响作用。

In recent years,the accelerated urbanization process has led to the high speed of urban population growth and the rapid increase of construction intensity in major cities,where a large number of high-density urban built-up areas were constructed.The urbanization process has greatly changed the urban ecological environment,resulting in heat island effect and other problems.Among the factors which affect the urban thermal environment,urban morphology plays an important role.Optimizing its design and alleviating the heat island effect is regarded as a feasible measure with great potential.However,the influential mechanism of urban morphology on the thermal environment is still unclear.Taking the typical high-density built-up area within the Fifth Ring Road of Beijing as the research area,we firstly divided it into basic units of 500 m side length grid corresponding to the size of urban blocks,and selected the key indicators of regulatory detailed planning for urban morphology control in the urban planning system.After calculating the average land surface temperature and the average of urban morphology indicators in each grid by remote sensing and spatial analysis techniques,we established OLS and GWR regression models to analyze the effect of building density,floor area ratio,and green space ratio on the urban thermal environment.The results showed that:(1)Urban morphology factors have a significant impact on the thermal environment.The increase of building density leads to the rise of land surface temperature(LST),while the increase of floor area ratio(FAR)and green space ratio leads to the decrease of LST.(2)The effect of each index on the thermal environment is spatially unstable.The building density around the main water body has the highest LST increment magnitude,and FAR here has an abnormally LST increment effect as well.The greenery ratio has a stronger cooling effect on the edge of the built-up area.And(3)the OLS model has a deviation in estimating the thermal environment effect of indices in particular areas,while the GWR model could reveal the impact of indices on the thermal environment more accurately.