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) in advance of issuing a heat warning. Based on ECCC’s heat warning, the Medical Officer of Health may issue a local Heat Warning if conditions are forecasted to last at least 2 days, or an Extended Heat Warning if conditions are forecasted to continue for 3 or more days.

WHAT HAPPENS DURING A HEAT WARNING OR EXTENDED HEAT WARNING?

Once the Medical Officer of Health declares a Heat Warning or Extended Heat Warning, notification of key response partners, community agencies and the public is initiated. Hot weather response activities focus on protecting vulnerable groups at increased risk for heat-related illness.