Heat and Thermal Stress Mitigation Strategies Evaluated over Montreal and Toronto, Canada

This project aims at providing decision-making guidance for heat-resilient strategies in Canada. Future climate projections highlight a significant increase of the number of days with excess heat in Canadian cities. Under the current climate, previous heat waves had an important impact on the public safety, while increasing the death rates.

Evaluations of scenarios for the urban landscape modifications are performed for Montreal and Toronto metropolitan areas with a numerical platform developed based on ECCC’s Numerical Weather Prediction (NWP) systems. Sub-km grid spacing (down to 250 m) are used in both external urban and land surface modeling (with the Town Energy Balance TEB and the Interactions between the Soil, the Biosphere and the Atmosphere ISBA) and coupled with the Global Environmental Multiscale (GEM) atmospheric model. Such systems are capable of providing forecasts of meteorological conditions and thermal stress indices (such as UTCI, WBGT, and Humidex) at the street level. Microscale NWP forecasting over Montreal reveals heat conditions heterogeneity over a large agglomeration during two consecutive heat waves in 2010, and in particular, persistent warm conditions during the night that prevent dwellers from resting. Results are shown for scenarios that are divided into the following categories of modification: radiative and materials properties, greening strategies, water management, anthropogenic heat fluxes, and the combination of measures. In general, these countermeasures are found to effectively decrease the impact of extreme heat conditions in cities, with a different amplitude and behavior during the day and the night. Greening strategies tend to be the more efficient strategies but they highly depend on the soil water availability.