Spatial distribution of heat vulnerability in Toronto, Canada

The frequency, intensity and duration of heatwaves are expected to increase in Toronto, Canada due to both climate change and the urban heat island effect. This poses a greater health risk to those who are most vulnerable to heat among a population of almost three million residents. Therefore, designing and implementing appropriate heat management measures requires information about how heat vulnerability is distributed across the city. To fill the knowledge gap, two distinct methods are examined in this study to quantitatively measure the spatial distribution of heat vulnerability in Toronto. Both heat vulnerability indices (HVIs) consist of three dimensions, exposure, sensitivity and adaptive capacity, that are aggregated from remotely sensed land surface temperature measurements and socio-economic census data. The first method uses principal component analysis to derive an HVI, while the second, simpler method assigns equal weight to each input variable to derive an HVI. The HVIs display a similar U-shaped pattern of high heat vulnerability across Toronto, with low heat vulnerability areas primarily located along the Lake Ontario shoreline and throughout the fluvial ravine system. Further cluster analysis reinforces this spatial pattern. Notably, this study highlights that low-income tower block communities are significantly more vulnerable to heat than the city average. The qualitative consistency between the two HVI methods allows for ease of adoption of the simpler, equal-weight method for future use by the city. Integration of HVI updates into municipal operations can allow city planners and managers to monitor and visualize heat vulnerability consistently over time, develop decision-support tools for heat emergency preparedness and response and assess the effectiveness of heat adaptation strategies.