Toronto's Heat Health Alert System

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.

Identifying Actions

As a response to the increasing severity of extreme heat events in Toronto, the City is working together with Toronto Public Health (TPH) to optimize the City’s heat-response plan through implementing and upgrading Toronto’s Heat Health Alert System. Toronto’s Heat Health Alert System includes a three-day forecast outlook. This synoptic-based approach starts with an air mass categorization for each forecast day based on weather conditions (temperature, humidex, dew point, wind speed and direction, air pressure and cloud cover). Then an algorithm is run to predict the likelihood of excess mortality under these air mass conditions; it is this likelihood that determines whether the Heat Health Alert System forecasts an Extreme Heat Alert, a Heat Alert or neither.


Toronto has implemented and updated its “Heat Health Alert System” as a response to extreme temperatures; the technical system used has changed in form since its inception in 1999, and now involves a three-day forecast outlook. Weather condition information is gathered and analyzed and likelihood scores are produced to predict the likelihood of excess mortality under the analyzed conditions. The Toronto Medical Officer of Health issues a “Heat Alert” when the likelihood of excess weather-related mortality exceeds 65 percent and an “Extreme Heat Alert” when the likelihood of excess weather-related mortality exceeds 90 percent. TPH conducts an annual review of the City’s hot weather response. Recent changes to the plan include an increase in the number of cooling centres and an increase in the number of transit tokens distributed to people in need of transportation to a cool place. TPH also received funding from NRCan in 2010 to develop a map-based decision support tool for public health staff and community partners to improve the delivery of health-protective services to the most vulnerable populations during extreme heat events. At the beginning of the summer, the City of Toronto and its partners provide the public with targeted information on the risks of extreme heat and on precautions to prevent heat-related illness and death. Various brochures are distributed and are available on the City’s Web site. Declaration of an alert by Toronto’s Medical Officer of Health activates specific responses under the City of Toronto Hot Weather Response Plan.

Outcomes and Monitoring Progress

Toronto’s Hot Weather Response Plan has increased awareness of problems related to extreme heat, contributed to the development of new programs and measures to combat the urban heat island effect, and helped facilitate the partnering of various City departments, non-governmental organizations and other local groups.

Next Steps

Toronto Public Health (TPH) is developing a mapping tool to visualize human vulnerability to extreme heat. The maps will incorporate numerous indicators of vulnerability, including surface temperatures, green space coverage, housing and social characteristics of at-risk populations, access to air conditioning, and the location of cool places. Due to be completed in 2011, the tool will help TPH and community partners identify and prioritize geographic hot spots for delivering resources during a heat alert. The City of Toronto also plans to use the tool for long-term climate adaptation planning. The City is now developing a Climate Change Risk Assessment process and electronic tool to be used in a variety of City Divisions. The process will include consideration of many extreme weather indicators, including extreme heat. The results of the risk assessment will enable staff to prioritize climate change risks and prepare appropriate adaptive actions.