Thermal effects of cool roofs and urban vegetation during extreme heat events in three Canadian regions

Abstract

The need to mitigate and adapt to a changing climate is becoming more urgent, especially in highly urbanized areas where a growing portion of the population lives. This study quantifies the effectiveness of two Nature-Based Solutions - cool roofs and urban vegetation - in the moderation of urban temperature during past Extreme Heat Events in the Ottawa-Montreal, Calgary, and Vancouver regions of Canada. The Weather Research and Forecasting model coupled with the multi-layer building effect parameterization and building energy model at a horizontal resolution of 1km is evaluated under diverse climates, and is used to simulate different levels of both NBS applied across each of the aforementioned regions. Increasing implementation of cool roofs and urban vegetation lead to reductions of near-surface air temperature and wind speed, and enhancements in relative humidity. The largest cooling occurred when both cool roofs and increased vegetation are implemented in each of the cities. The largest cooling effect was found in Vancouver, where a maximum reduction of 3.5°C in 2m air temperature could be felt, while the weakest effect was found in Ottawa at 1.2°C across the city.