What you need to know about heat alerts in British Columbia — and how to respond to them

Heat warnings blanket much of the province and are expected to continue over the next few days, but despite record-breaking temperatures in some areas, no extreme heat emergencies have been declared.

However, the province has been working on a system of alerts and responses.

After nearly 600 British Columbians died as a direct result of last year's heat dome — in what is considered Canada's deadliest weather event on record — it created a committee to plan for future extreme hot weather.

The B.C. Health Effects of Anomalous Temperatures Coordinating Committee (B.C. HEAT Committee) was established in January 2022 and brought together several provincial agencies, including the B.C. Centre for Disease Control, the Ministry of Health and Health Emergency Management.

That committee developed a two-tiered heat alert response system for extreme heat events: heat warning and extreme heat emergency.

Here's how it works:

What is a heat dome

Extreme heat events, more commonly known as heat waves, involve high temperatures and sometimes high humidity.

They are extended periods of extreme heat and can occur anywhere in Canada, although they are most common in the southern regions of the country.

A heat dome — like the deadly June 2021 event — occurs when a high-pressure system traps heat near the earth's surface and gets held in place by a blocked jet stream.

"It's stagnant air," explains Environment Canada meteorologist Armel Castellan. "You've got this dome, this lid. It's not moving very much."

Castellan says heat waves in B.C. are projected to become more intense, more frequent and longer in duration.

A report by the HEAT Committee estimates that they will occur every three to 10 years by 2050 and that average annual temperatures will increase by 1.7 C in Greater Vancouver by the 2050s and 2.7 C by the 2080s.

Why does B.C. need a heat alert system

The province says it wants to be prepared for the rise in extreme heat events. 

"It's vital that we take the lessons we learned from last year's devastating heat dome to make sure that the province and our health-care system are as prepared and resilient as possible during extreme heat," said Health Minister Adrian Dix in a June news release.

Heat waves are the leading cause of weather-related death in Canada.

Exposure to extreme heat can cause body temperature to rise quickly and can lead to illnesses including heat cramps, heat exhaustion, heat stroke and hyperthermia. This can be especially dangerous for vulnerable populations like older adults, those with chronic illnesses, mental illness and poor people.

"People do not die because it's hot outside. They die because it's hot inside," explained Sarah Henderson, scientific director of Environmental Health Services at the BCCDC. "This is in places that don't have air conditioning or don't have functioning air conditioning."

What is the B.C. HARS

B.C.'s Heat Alert Response System (HARS) uses specific heat criteria to determine what type of alert needs to be issued to British Columbians so they can prepare for hot weather. The criteria take into account daytime and nighttime highs and lows and are specific to each region of the province.

For example, a "heat warning" would be issued for southwest B.C. when, for at least two days in a row, daytime maximum temperatures are expected to reach 29 degrees or warmer and nighttime minimum temperatures are expected to fall to 16 degrees or warmer.

For the Interior, the threshold temperatures would be daytime highs of 35 degrees and nighttime highs of 18 degrees for two consecutive days.

Regional B.C. threshold for heat warnings

• Southwest: daytime high of 29 C, nighttime low of 16 C
• Fraser: daytime high of 33 C, nighttime low of 17 C
• Southeast (Interior region of B.C.): daytime high of 35 C, nighttime low of 18 C
• Northeast: daytime high of 29 C, nighttime low of 14 C
• Northwest: daytime high of 28 C, nighttime low of 13 C

When the specific regional criteria triggers are met, the ECCC will issue a "heat warning" to the public and advise them to follow health and safety guidelines, including:

• Staying hydrated.
• Minimizing physical activity, especially during the hottest hours of the day.
• Staying in cooler indoor and outdoor spaces.
• Turning on air conditioning.
• Taking a cool shower.
• Applying damp clothes or towels to your skin to cool down.

A weather event becomes an "extreme heat emergency" when criteria for a heat warning have been met, and daily highs are forecast to increase day to day for three or more days, according to the HEAT committee's definition. That kind of weather emergency comes with an estimated 20 per cent increase in mortality.

If a heat warning becomes an extreme heat emergency, the province releases an alert through the national public wireless alerting system, Alert Ready, which is also used for Amber Alerts and tsunami warnings.

The HEAT committee report advises that, during a heat emergency, people monitor indoor temperatures and be aware that prolonged exposure to temperatures over 26 degrees can be dangerous to vulnerable people.