How effective are adaptation strategies in reducing climate change–induced urban heat stress exposure? A case study of cool roofs and urban forestry in Vancouver and Victoria.

The urban heat island effect, a direct consequence of urbanization, compounded by climate change impacts, poses challenges to population heat stress exposure. Coastal cities, which experience land-sea breezes, are facing additional complexities to address this exposure concern.

This study utilizes the high-resolution Weather Research and Forecasting model coupled with a single-layer Urban Canopy Model to assess the effects of two well-established heat mitigation strategies, i.e., cool roof and urban forestry, on temperature dynamics and population heat stress exposure. Two coastal cities in Western Canada, Vancouver and Victoria, are taken as a testbed. We analyze two climate change scenarios based on the Coupled Model Intercomparison Project Phase 6, covering near- and far-future projections under SSP2-4.5 and SSP5-8.5 pathways.

The results indicate that by the end of the century, the population's exposure to heat stress under SSP5-8.5 will be three times greater than under SSP2-4.5, the urban population growth being the main factor driving increased exposure. Increasing urban vegetation can help reduce urban heat islands and exposure, but planting more trees in already vegetated areas might not yield further cooling benefits and could worsen water management issues during droughts. Conversely, widespread use of reflective roofs or efficient solar panels provides stronger advantages by reducing temperatures both indoors and outdoors, but the extent of their impacts is limited.

This study shows that both heat mitigation strategies are insufficient to counter the projected impacts of climate change on daily temperature extremes, heat-stress days, and population exposure. This emphasizes the crucial necessity of reducing greenhouse gas emissions for lowering population exposure to heat stress rather than betting on climate adaptation strategies.