School of Architecture and Urban Planning, Nanjing University, No. 22, Hankou Road, 210093, Nanjing, China.
International Institute for Earth System Science (ESSI), Nanjing University, No. 163, Xianlin Ave, 210023, Nanjing, China.
Sci Total Environ. 2019 Dec 15;696:133976. doi: 10.1016/j.scitotenv.2019.133976. Epub 2019 Aug 20.
The thermal performance of green roofs is usually site-specific and changes temporally. Hence, thermal performance evaluation is necessary to optimize green roof design and its cooling effect. In this paper, we evaluated the outdoor spatio-temporal performance of a full-scale extensive green roof (EGR) in Nanjing, China throughout a summer at three heights (30, 60and 120cm). We found the EGR exhibited an overall slight diurnal cooling effect at all three heights (-0.09, -0.23, and - 0.09 °C, respectively), but there was an obvious warming effect at a couple of specific hours during daytime. Especially on sunny days, the maximum warming effect at all three heights was 1.59, 0.59, and 0.38 °C, respectively. During the night, the EGR had a pronounced cooling effect of -0.63, -0.40, and - 0.15 °C, respectively. Among the weather scenarios, sunny days had the highest impact on the EGR's thermal performance, while effects were less pronounced on cloudy and rainy days. The average range of hourly air temperature difference at 30 cm between EGR and a bare roof on selected days was 4.02 (sunny), 2.67 (cloudy), and 0.74 °C (rainy). The results of multiple-regression analyses showed strong and significant correlations of air temperature difference between the EGR and a bare roof with differences in relative humidity, net radiation, several measures of soil and surface temperature, and soil moisture as well as average solar radiation, air temperature and wind speed. The results implied that both the components of the EGR, such as green vegetation and the soil substrate layer, and the microclimate created by the EGR can feed back and contribute to the thermal performance of an EGR. Through this full-scale EGR research in a subtropical monsoon climate, we provide the scientific basis and actionable practices for green roof planning and design to alleviate the urban heat island effect towards designing climate-resilient cities.
绿色屋顶的热性能通常具有场地特异性，并随时间变化。因此，需要进行热性能评估，以优化绿色屋顶的设计及其冷却效果。本文在中国南京的一个全尺寸扩展型绿色屋顶（EGR）进行了夏季室外时空性能评估，分别在三个高度（30、60 和 120cm）进行。结果表明，EGR 在所有三个高度都表现出轻微的日夜间冷却效果（分别为-0.09、-0.23 和-0.09°C），但在白天的几个特定时间有明显的变暖效应。特别是在晴天，三个高度的最大变暖效应分别为 1.59、0.59 和 0.38°C。在夜间，EGR 的降温效果明显，分别为-0.63、-0.40 和-0.15°C。在各种天气情景中，晴天对 EGR 热性能的影响最大，而阴天和雨天的影响则较小。在选定的日子里，30cm 高处 EGR 与裸屋顶之间的小时空气温差平均范围分别为 4.02°C（晴天）、2.67°C（阴天）和 0.74°C（雨天）。多元回归分析结果表明，EGR 与裸屋顶之间的空气温差与相对湿度、净辐射、土壤和表面温度的几个测量值以及土壤水分和平均太阳辐射、空气温度和风速之间存在强烈而显著的相关性。结果表明，EGR 的组成部分，如绿色植被和土壤基质层，以及 EGR 所创造的微气候，都可以反馈并有助于 EGR 的热性能。通过在亚热带季风气候下对全尺寸 EGR 进行研究，为绿色屋顶规划和设计提供了科学依据和可行的实践，以缓解城市热岛效应，朝着设计气候适应型城市的方向发展。
