绿色屋顶降温效应的多维时空变化特征

Measuring the performance of green roof cooling effects from a multi-dimensional perspective

准确量化和挖掘绿色屋顶降温效应的时空特征是科学评价其热环境调控服务效益与潜力的重要前提。以南京市金陵小学轻型佛甲草绿色屋顶为例,基于夏季典型气象条件下的定点观测数据,率定ENVI-met模型中的相关参数,验证模拟结果的有效性;从传统"点"和"面"角度测度了绿色屋顶降温效应的二维变化特征,并采用三维"冷岛"逐时降温累积值和降温质心的时空变化来定量刻画绿色屋顶降温效应的四维变化特征(即三维"冷岛"随时间变化的特征),进而阐明其主要影响因素。研究结果表明:(1)轻型佛甲草绿色屋顶在日间(6:00-18:00)降温效应很弱,但在夜间(19:00-次日5:00)降温效应比较明显;(2)基于三维空间刻画的日夜间降温效应差异较传统二维方法测度的结果更为明显,绿色屋顶点、面与三维降温效应日夜间比值分别为3.1、5.0和8.1;(3)降温质心与降温强度在空间上呈现明显的集聚分布特征,夜间的降温强度与集聚程度明显高于白天,夜间的降温质心在绿色屋顶几何中心上方集聚,而白天质心分布较为分散且向靠近裸露屋顶一侧偏移;(4)绿色屋顶降温效应时空变化特征主要受下垫面属性、植被生理特征和局地微气象因子的多重影响。与传统的二维降温效应分析相比,从"四维时空变化"角度实现了对绿色屋顶降温效应更加客观的定量表征,可为其成本收益分析与建设效益评价提供重要的量化手段与决策依据。

Effectively measuring cooling performance is important for evaluation of the thermal environmental regulation services of green roofs.Using the case study of the extensive green roof on the buildings of Jinling primary school,Nanjing,China,this study modeled the effects of green roof on local microclimate by using simulation-based ENVI-met software,and the simulation results were further validated based on the typical summer meteorological weather observations.Using meteorological data and ENVI-met simulation results,the cooling performance of the green roof was first analyzed from"point"and"surface"perspectives,similar to that by most previous studies,and then a novel analysis method was developed and applied to more comprehensively analyze the cooling performance from a 4 D perspective.Accordingly,the hourly cooling effect and the spatio-temporal variations in the"cooling island"mass center were quantified,and simultaneously,the related factors potentially affecting the cooling performance of the roof were explained.The results showed that(1)the cooling effect of extensive green roof with Sedum lineare Thunb.was weaker during the daytime(6:00-18:00)than during nighttime(19:00-5:00 the following day).(2)The diurnal cooling effect was much more obvious when measured from a three-dimensional perspective than a two-dimensional one(ratio 3.1,5.0,and 8.1 for the hourly cooling effects during daytime to that of nighttime from a point,surface,and three-dimensional perspective,respectively).(3)The mass center and intensity of the cooling island showed a pronounced spatial aggregation within the modeled area.The intensity of the cooling island was stronger during nighttime than during daytime.The mass centers gathered above the geometric center of the green roof during nighttime,whereas at nighttime,they scattered and shifted to the side of the bare roof.(4)The overall green roof-cooling performance indicated that the cooling effect was mainly affected by the properties of the underlying surface,the physiological characteristics of the vegetation,and the local micro-meteorological factors.Compared with that of the traditional method,the measurement from the four-dimensional perspective,achieved a more objective assessment of the green roof-cooling effect.The proposed novel method will be extremely helpful in the cost-benefit analysis and of green roof-construction projects.