Harnessing street shade to mitigate heat stress: An in-situ parallel investigation under extreme heat conditions in tropical Singapore

In the face of global rising temperatures and excessive urban heat, developing effective heat mitigation strategies has become increasingly urgent. Street shade, a typical cooling shelter for urban dwellers, has been primarily investigated for outdoor thermal comfort but not extensively under extreme heat conditions. This study explores the cooling efficacy of diverse street shade types in mitigating urban heat, thereby facilitating cities and their residents' adaptation to climatic shifts. We conducted in-situ measurements during an extremely hot afternoon, measuring thermal and visual environments across 20 pairs of parallel sites (sunlit vs. shaded) in a high-density district of tropical Singapore. Subsequently, we analyzed thermal comfort, represented by the Universal Thermal Comfort Index (UTCI), heat stress risks, and view factors of the sky, greenery, and buildings, and their interaction with heat stress relief. Our findings highlight three key points: Firstly, all street shade types improved outdoor thermal conditions, with average decreases of 0.8 °C in air temperature, 10.0 °C in mean radiant temperature, and 3.1 °C in UTCI. Secondly, street shade generally reduced heat stress severity by 20 % in the 'very strong heat stress' category and 12 % in the 'strong heat stress' category. Thirdly, the cooling efficacy of street shade was not solely dependent on changes in any single view factor. The results demonstrate the significant cooling benefits provided by street shade during extreme heat conditions. This study not only underscores the crucial role of street shade in mitigating heat stress but also offers valuable guidance to urban planners and designers in creating more liveable, sustainable, and climate-adaptive cities.