Environment Canada projects that by the latter part of this century, Toronto will average 65 days per year where the temperature exceeds 30°C, more than four times the historic average between 1961 and 1990. This represents a critical concern that will disproportionately impact the health and wellbeing of the city’s more vulnerable populations. The health risks increase substantially when people experience prolonged exposure to heat without significant cooling intervals. Socially isolated seniors are at highest risk of heat-related illness and death. Other at-risk groups include children, people with chronic and pre-existing illnesses including mental illness, low-income households, and adults who are marginally housed or homeless. Toronto has had a heat warning system since 1999. The first heat warning system used a threshold of a one-day forecast of humidex over 40°C. Since 2001, Toronto Public Health has adopted the Heat Health Alert System as the basis for declaring alerts. This system is based on a synoptic approach that assesses the historical relationship between mortality levels and weather conditions.
As a response to the extreme heat events in the City of Toronto and given that Environment Canada projects Toronto will average 65 days per year where the average temperature exceeds 30°C, the City implemented a Heat Health Alert System (HHAS) in 2001. The HHAS issues a city-wide “Alert” when the likelihood of excess weather-related mortality exceeds 65 percent. The “Heat Alert” triggers several protocols, including the opening of seven designated cooling centres. Toronto’s Hot Weather Response Plan has contributed to increased awareness and the long-term safety of its population. Given the human health implications of prolonged heat exposure, especially for at-risk groups such as seniors, children, and individuals with pre-existing illnesses, the HHAS is considered a prudent action in building climate resilience.