Centre for Urban Science and Engineering, Indian Institute of Technology Bombay, Mumbai 400076, India.
Centre for Urban Science and Engineering, Indian Institute of Technology Bombay, Mumbai 400076, India; Interdisciplinary Programme (IDP) in Climate Studies, Indian Institute of Technology Bombay, Mumbai 400076, India; Centre for Research in Arts, Social Science, and Humanities, University of Cambridge, UK.
Sci Total Environ. 2019 Jun 15;669:872-886. doi: 10.1016/j.scitotenv.2019.03.152. Epub 2019 Mar 12.
The thermal profile of the urban built-up area is essential for reducing the impact of built-up areas on urban heat stress. This study quantifies the variations in the outdoor thermal profile of built forms in a heterogeneous urban area. A two-step process was adopted to quantify built form induced heat stress. The build form typologies referred to as Urban Built Form (UBF) were clustered based on parameterised build form indices (sky view factor, built height etc.) using statistical data reduction. The heat stress of the categorised UBFs was then examined through field measurements and radiation simulation model. Variations in thermal variables were assessed using three indices - Cooling Potential (CP), Humidex (Hx) and Mean Radiant Temperature (Tmrt) that collectively define the thermal profile of each UBF. A novel Heat Stress Risk Index (HSRI) was conceptualised and computed to represent the aggregate risk of a particular UBF towards heat stress. It was found that among the UBFs, the medium-rise compact (UBF 4) show lowest rate of cooling, exposure to high Tmrt, and high discomfort levels throughout the day and therefore exhibit thermally stressed profile. High rise-open typologies (UBF1) have high Tmrt and Hx during the noon (12:00 to 14:00 h), but their high cooling potential reduces the thermal impact of its built form during the cooling hours (18:00 to 20:00 h). Three thermal indices provide varied aspects of thermal performance of UBFs and HSRI cumulatively represents the heat stress risk of the UBFs. This study is a proof of concept, that uses empirical evidence to demonstrate thermal variations in urban built forms during calm and clear weather conditions. Results indicate the significance of built form indices as a policy variable for framing climate sensitive urban development regulations that aim to achieve a thermally efficient built environment.
城市建成区的热环境对缓解城市热应激至关重要。本研究量化了异质城市地区建成形态的室外热环境变化。采用两步法量化了建成形态引起的热应激。所提到的建成形态类型学被归类为城市建成形态（UBF），基于参数化的建成形态指数（天空视野因子、建筑高度等）使用统计数据降维聚类。然后通过现场测量和辐射模拟模型来检查分类 UBF 的热应激。使用三个指数评估热变量的变化 - 冷却潜力 (CP)、湿热指数 (Hx) 和平均辐射温度 (Tmrt)，它们共同定义了每个 UBF 的热环境。提出了一种新的热应激风险指数 (HSRI)，以代表特定 UBF 对热应激的总体风险。研究发现，在 UBF 中，中高层紧凑型（UBF4）冷却率最低，全天暴露在高 Tmrt 下，舒适度水平较高，因此表现出热应激特征。高层开敞型（UBF1）在中午（12:00 至 14:00 时）具有较高的 Tmrt 和 Hx，但在冷却时间（18:00 至 20:00 时）其高冷却潜力降低了其建筑形态的热影响。三个热指数提供了 UBF 热性能的不同方面，HSRI 累积代表了 UBF 的热应激风险。本研究是一个概念验证，使用经验证据演示了在平静和晴朗天气条件下城市建成形态的热环境变化。结果表明，建成形态指数作为制定气候敏感城市发展法规的政策变量的重要性，这些法规旨在实现热效率高的建成环境。
