Natural shading vs. artificial shading: A comparative analysis of their cooling efficacy in extreme hot weather

Abstract

Shading, comprising both natural and artificial coverings, is an efficient and effective strategy to reduce heat stress in outdoor environments. Despite its recognized efficiency, there is limited comparative insight into the cooling performance of natural and artificial shading. This study examined the cooling efficacy of two covered walkways and two tree canopies, concerning microclimate conditions by various variables and thermal stress quantified by four thermal indices. Our findings highlight three key points: Firstly, the average cooling effects provided by natural and artificial shading were comparable, including reductions in air temperature (1.42 °C vs. 1.31 °C), mean radiant temperature (15.93 °C vs. 13.71 °C), and Physiological Equivalent Temperature (PET) (9.06 °C vs. 9.70 °C), Universal Thermal Climate Index (UTCI) (4.71 °C vs. 5.08 °C), and Hong Kong Heat Index (HKHI) (2.36 °C vs. 2.50 °C). Secondly, it is inconsistent which shading solution is better for microclimate improvement and heat stress alleviation, which is affected by canopy materials, configurations, and tree species. Thirdly, the four indices presented an inconsistent pattern in heat stress assessment. Notably, PET and UTCI showed similar patterns, while HKHI and modified PET presented lower sensitivity to high heat stress. This study offers valuable insights for urban designers to create sustainable shaded communities and also initiates a discourse for revising local heat warning systems, considering various thermal stress indices.