What is the Heat Warning and Information System?

The Heat Warning and Information System (HWIS) is a coordinated provincial system that provides a consistent approach for processing and issuing heat warnings in Ontario, in order to better protect residents, vulnerable community members and visitors during the summer season. It was developed jointly by Environment and Climate Change Canada, Health Canada, the Ontario Ministry of Health and Long-Term Care, and Public Health Ontario, in consultation with provincial health units.

The HWIS provides criteria for issuing heat warnings. These criteria were selected after an extensive review of epidemiological evidence about the links between temperature, humidity, and health outcomes including mortality and illness.

How the HWIS works

The EOHU receives weather forecasts from Environment and Climate Change Canada (ECCC). Based on ECCC’s heat warning, the ECCC may issue a local Heat Warning if conditions are forecasted to last at least 2 days. The EOHU will then advise residents of the forecasted heat event and provide recommendations on how to protect themselves from heat-related illnesses. Heat warnings are based on the following triggers:

What happens during a Heat Warning?

Once the ECCC issues a Heat Warning, the EOHU will notify key response partners, community agencies and the public. Heat weather response activities focus on protecting vulnerable groups at increased risk for heat-related illness.

In exceptional cases of extended heat episodes, municipalities may open cooling centres, and some public pools may have extended operating hours. For more information, contact your local municipality.