The Problem

Combinations of heat and humidity put human health at risk, adding to pressures on Canada's healthcare system.

Extremes can cause deaths, as seen in Chicago (1995), Europe in 2003, and in California in 2006. Municipalities need a reliable system to help plan and initiate actions to warn vulnerable populations, such as the elderly, ill and homeless, to seek assistance before they are in danger.

Under an earlier heat alert system, the City of Toronto called an alert when the "humidex" exceeded 40°C for two or more consecutive days. The humidex was devised by Canadian meteorologists to combine temperature and humidity into one number to reflect the perceived temperature. However, using a 40°C threshold for an alert was based on a military safety standard and did not meet the needs of urban populations.

Seeking Solutions through S&T

In 2000, the City of Toronto Public Health Department, in partnership with the Toronto Atmospheric Fund and with assistance from Environment Canada and the University of Delaware, initiated a scientific investigation into developing a new Heat Alert and Emergency system. Climatological and epidemiological analyses would drive this new system.

Toronto became one of seven cities in the world to implement a pilot system. Using weather predictions provided by Environment Canada, the pilot was based on 46 years of climate data and 17 years of epidemiological evidence. Researchers found that certain climatic conditions were associated with significantly higher death rates in Toronto. They also determined that the impacts of heat in Toronto, as reflected in mortality statistics, were greater for heat events early in the warm season (e.g., April to May) and for persistent or multiple day heat events (heat waves).

Transforming Knowledge into Action

Who can use these results?

Under the new Heat Health Alert System, the Toronto Medical Officer of Health calls either a Heat Alert or an Extreme Heat Alert based on the following criteria:

Heat Alert – when Environment Canada's meteorological forecasts and results from the epidemiological study project a 65 to 90 percent chance of increased mortality for Toronto residents.

Extreme Heat Alert – when Environment Canada's meteorological forecasts and results from the epidemiological study project a greater than 90 percent chance of increased mortality for Toronto residents.

When a Heat Alert is called, Toronto's Response Plan triggers the following actions:

• more than 900 individuals and community agencies work with vulnerable populations;
• a 12-hour help line answers heat-related inquiries from the public and responds to requests;
• emergency preparedness is enhanced, as required for any other alert or emergency response (e.g., ambulance, police);
• delivery of bottled water is coordinated for vulnerable groups.

In addition, when an Extreme Heat Alert is called:

• recreational facilities extend their hours of operation;
• community cooling centres are opened and transportation to these centres is provided, as required.

Benefits to Canadians

A formal benefit analysis of the Toronto pilot has not yet been completed, but continuing demands for these services suggest Canadian communities recognize the benefits. Community leaders believe this service decreases the number of premature deaths related to heat stress in vulnerable populations and improves the quality of life for vulnerable populations during heat alerts. Many communities are also asking for scientific studies that can capture the health care needs or morbidity relationships (e.g., hospital admissions from combined heat and air quality impacts) associated with hot weather events.

To continually improve the benefits of this program for Canadians, Environment Canada researchers began studying the synergistic impacts of air quality and heat stress on mortality risks in 2002, including analysis of their potential implications under changing climate conditions. The study concluded that the changing climate has the potential for doubling to tripling potential mortalities from heat and air quality related events on severe heat days (depending on the city considered) unless adaptation actions are taken and air quality emissions are reduced.

For more information:

Environment Canada's EnviroZine: The Heat is On

Living in Toronto: Heat Alerts Website

Historical Heat Related Events in Ontario

An Analysis of Climate Change Impacts on Human Mortality in South Central Canada (PDF: 230 kB, download free reader)

Heat Watch/Warning Systems Save Lives: Estimated Costs and Benefits for Philadelphia 1995-98 (PDF: 85 kB, download free reader)

S&T Liaison | Tel 905 336 4513 | Fax 905 336 4420
© Her Majesty the Queen in Right of Canada, represented by the Minister of Environment, 2007.
Catalogue No. En164-15/2-2007E-PDF; 978-0-662-46657-4