屋顶绿化对高密度城市片区热岛效应的影响——以广州国际金融城起步区为例

Influence of Green Roof on Heat Island Effect in High-density Urban Area:The Case of Start-up Zone of Guangzhou International Financial City

城市核心区的高密度开发方式,会对生态环境造成诸多负面影响,基于生态低碳的设计理念对高密度片区的开发尤为重要。屋顶绿化因其节约和高效利用空间的特点,成为此类地区应对用地紧张和环境问题的理想手段之一。很多学者都在探究绿化与城市热岛效应之间的关系,然而目前并没有针对如何使用给出具体的建议。以广州金融城起步区为例,通过三维气候模拟软件ENVI-met system构建模型,对屋顶绿化在缓解城市热岛效应方面的影响进行分析,模拟结果证实了屋顶绿化是缓解高密度地区热岛效应、增加城市绿地面积、促进城市生态环境优化的有效手段。提出一定规模、合适高度的屋顶绿化在高密度地区可作为"绿色缓冲区"和"绿地斑块",弥补绿化密度低带来的高层建筑以外的区域与集中绿地"冷岛"隔离的微气候问题。

Along with the rapid development of urbanization and intensification,a growing number of high building density regions have been built in China.These high-density developing places play a significant role in the production of Urban Heat Island Effect(UHIE).In the past decades,increasing serious environmental problems woke the local governments and developers up to the need of ecological design and drove them to take action accordingly.One important measure taken by Chinese government is to set up a strict greening rate(Green space area/Total land area)in order to guarantee a certain green land to mitigate UHIE.Yet it would be difficult to reach the standard for high-density region where land is tension with built-up buildings.Developing green roof offers an alternative opportunity to resolve this conflict.Previous researches have showed that roof greening not only made efficient use of urban space,but also had quite a large value in contrasting the urban heat island effect.Researches in this field are becoming more quantitative and the research subject has gradually moved from a whole city toward a city site.Although these existing studies have involved the correlation discussion between city-related factors and UHIE,they do not really conclude any practical suggestion for designing a city site.Our research analyzes the performance of green roof by numeric simulation method to see to what extent this measure constitutes UHIE mitigation and what should respect notice while using green roof in high-density regions.Our paper employs a mixed method approach that combines qualitative and quantitative analysis.Three-dimensional climate simulation software ENVI-met is chosen as the evaluation tool.A site of 132.4 hectares in Guangzhou Financial City(plot ratio is 3.8)is used as the study model.Comparisons take place under different situation:optimization model(with green roof)and benchmark model(without green roof)on two times of a day(2PM and 12PM).It is found that in general,the temperature that the benchmark model showed was much lower than that the optimization model did.In particular,the low temperature area(temperature<27℃)of optimization model was significantly larger than that of benchmark model(temperature<28℃).The high temperature area(temperature around 29℃)of optimization model was also significantly less than the benchmark model.This study indicates that roof greening is an effective mean to relieve heat island effect,increase the urban green space area and promote urban ecological environmental optimization in high density area.This paper also put forward the thought that roof greening,with a certain scale and an appropriate height,can be used as“green buffer”and“green patches”,to solve the problem caused by low planting density which will lead to the isolation of area inside the concentrated green land and outside the high-rise buildings around it.Therefore,building green roof is worthy to be popularized as one of the proper measures dealing with land tension and environmental problems in high building density regions.