Cover photo shows an example of image transformation from panorama to fisheye view: (a) panorama, (b) fisheye view, and binarised fisheye view of (c) sky, (d) trees, and (e) buildings.
Rapid global urbanisation and a heating planet will mean rising heat stress for city dwellers. An aging population will compound the impact on human health for heat-related illnesses such as heat stroke, exhaustion, and cramps.
Street shade in the form of greenery and man-made structures have demonstrated cooling benefits in controlled experiments. However, until now, studies have not analysed diverse elements of street shade and their ability to mitigate heat stress in outdoor conditions – particularly in the context of a tropical city such as Singapore.
Dr Ronita Bardhan from the Department of Architecture at the University of Cambridge has found that street shade in its various forms can provide effective cooling to outdoor locations; decreasing temperatures by an average of 3.1°C when measured using the heat stress metric Universal Thermal Comfort Index (UTCI).
“Our study has shown that not just one type of street shade, but diverse street shade types have cooling efficacy and was able to reduce heat stress severity at all test locations. New town planning should consider that shading is not just greenery. Findings such as these can help create climate-responsive adaptation strategies to improve outdoor thermal comfort,” said Dr Bardhan.
Seeing the sky with a fisheye
The research group selected 20 pairs of sites in Singapore, one sunlit and one shaded, to capture ‘fisheye’ photos using a special wide-angle lens. The sky, greenery, and buildings were isolated into visual factors (view factors) to quantify the amount of “sunlit” or “shade” at each site (see the cover photo).
Air and wind measurements were collected to calculate the level of heat stress according to the UTCI, a comprehensive index for estimating heat stress in outdoor spaces.
“Singapore provided many test sites due to the large amount of shading infrastructure such as overhead footbridges, sheltered public corridors, and pavilions. Studies like these in tropical climates are critical to understanding how a majority of the global population in the Southern Hemisphere will be impacted by a warming climate,” said Prof Thomas Schroepfer, Programme Director of Future Cities Laboratory Global.
Different ways to keep cool
Sites with substantial artificial shade or greenery both had strong cooling potential with a decrease of average UTCI from 3 °C to 5 °C. The more severe the heat stress, the more cooling potential could be achieved.
However, not all paired sites consistently decreased in sky view factor measurements as they compared “sunlit” and “shade” locations, indicating the complexity of city structures and layout. A “shade” location could still have a high sky view factor. High-density urban configurations such as high-rise buildings showed the cooling potential of average UTCI from 3 °C to 4 °C, highlighting how sky view factor measurements should consider sun exposure impacts for thermal comfort analysis.
Surface temperature, which measures the heat emitted from surrounding objects, was also identified as a key factor in assessing the impacts of urban morphology on the cooling potential of street shade or outdoor thermal comfort.
Urban health is human health
“This preliminary study identifies how the built environment shapes our exposure to health risks. In the larger context of the upcoming Health-Driven Design for Cities (HD4) programme, I will work on scaling the urban stressors that have a direct impact on health outcomes. The idea is to identify urban exposures modified due to certain built environmental configurations that surpass critical levels of health stresses and result in poor health. In doing so we aim to improve the upstream determinants of health that promote healthier longevity,” said Dr Bardhan.
“It was a great start as a Principal Investigator at CARES to conduct a study with Singapore-ETH Centre’s (SEC) Future Cities Laboratory Global. CARES and SEC are both research entities under the same funding programme in Singapore called CREATE. I look forward to expanding more ideas with our CREATE partners working on similar research themes for human health and its potential”.
Read the full paper: “Harnessing street shade to mitigate heat stress: An in-situ parallel investigation under extreme heat conditions in tropical Singapore” (DOI: 10.1016/j.scitotenv.2024.177864) published in Science of The Total Environment.
The study was part of a preliminary review for the CARES-hosted Health Data Driven Design for Cities (HD4) programme. HD4 is funded by the National Research Foundation, Prime Minister’s Office, Singapore under its Campus for Research Excellence and Technological Enterprise (CREATE) programme.
