Heat warning and information system harmonization
Backgrounder
Environment and Climate Change Canada (ECCC) will implement a new heat warning and information system in Ontario in May 2016. The new heat warning system was developed after extensive engagement with several health stakeholders including Health Canada, the Ontario Ministry of Health and Long-Term Care, and local public health units.
ECCC will issue heat warnings 18 to 24 hours in advance of an extreme heat event. If two consecutive days of weather that meets or exceeds the criteria set (daytime highs and nighttime lows) are expected, a heat warning will be issued.
Under the new system, there are three regions, with criteria based on health evidence and climatology for each region (Figure 1). People living in areas with cooler climates can be more susceptible to extreme heat than those who are regularly exposed to hot environments and have had an opportunity to acclimatize to warmer temperatures.
In addition, ECCC is providing early notification to public health units by notifying them in advance of issuing a heat warning. This allows for local officials to enhance weather monitoring, intervene with those most vulnerable and to get prepared for the potential heat warning.
As a result of the new system, Ontarians may see changes in the number of heat warnings being issued for some regions. Given that the new criteria requires two consecutive days of meeting criteria conditions rather than one, the majority of Southern Ontario will likely observe fewer warnings. However, for many locations in Northern Ontario there may be an increase in the number of warnings, because the heat warning criteria can be met at lower temperatures or humidex conditions than in southern Ontario (in an effort to account for region-specific heat-health relationships due to things like acclimatization).
Prior to 2015, there was no consistent approach among Ontario public health units for issuing and responding to heat warnings to reduce heat-related deaths and illness. Ontario public health units used various different criteria for activating heat alerts and response plans.
In 2012, ECCC and Health Canada came together to improve public health messaging and heat warning criteria. The project aimed to help reduce heat health risks and ensure consistency of warnings. Public Health Ontario and Health Canada developed the health-related criteria for the new Ontario heat warningson the relationship between health effects, climate, and population characteristics.
Figure 1: Region-specific heat warning criteria
Tmax represents maximum daily temperature. Tmin represents minimum nighttime temperature.
Northern Ontario
- Tmax ≥ 29°C and Tmin ≥ 18°C OR Humidex ≥ 36
- 2+ days
Southern Ontario
- Tmax ≥ 31°C and Tmin ≥ 20°C OR Humidex ≥ 40
- 2+ days
Extreme Southwestern Ontario (Windsor area)
- Tmax ≥ 31°C and Tmin ≥ 21°C OR Humidex ≥ 42
- 2+ days
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Hon. Catherine McKenna Environment and Climate Change Canada Nature and Environment