Outdoor thermal performance of heterogeneous urban environment: An indicator-based approach for climate-sensitive planning

Surabhi Mehrotra; Ronita Bardhan; Krithivasan Ramamritham

doi:10.1016/j.scitotenv.2019.03.152

Outdoor thermal performance of heterogeneous urban environment: An indicator-based approach for climate-sensitive planning

Sci Total Environ. 2019 Jun 15:669:872-886. doi: 10.1016/j.scitotenv.2019.03.152. Epub 2019 Mar 12.

Authors

Surabhi Mehrotra¹, Ronita Bardhan², Krithivasan Ramamritham³

Affiliations

¹ Centre for Urban Science and Engineering, Indian Institute of Technology Bombay, Mumbai 400076, India. Electronic address: surabhi_m@iitb.ac.in.
² 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. Electronic address: ronita.bardhan@iitb.ac.in.
³ Department of Computer Science and Engineering (CSE), Indian Institute of Technology Bombay, Mumbai 400076, India.

PMID: 30897443
DOI: 10.1016/j.scitotenv.2019.03.152

Abstract

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_X) 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.

Keywords: Cooling potential; Heat stress risk; Thermal index; Thermal performance; Urban built form.