Heat Alert: How to Stay Safe and Informed During Extreme Heat Waves

Heat alerts are becoming increasingly common across Canada as the frequency and intensity of heat waves rise. Issued by Environment and Climate Change Canada (ECCC), a heat alert serves as a critical public safety warning, helping communities stay informed about dangerously high temperatures and humidity levels.

This guide will walk you through everything you need to know about heat alerts—what they are, how they’re issued, and why they matter. We’ll explore the science and public health strategies behind regional heat alert criteria, highlight real-world examples, and share actionable tips to help individuals and communities stay safe. As climate change continues to drive more extreme heat events, understanding and responding to heat alerts is more important than ever.

What Is a Heat Alert and Why It Matters

A heat alert is a critical public notification issued when weather conditions—such as high temperatures or humidity—pose serious health risks. These alerts are more than just weather advisories; they’re vital warnings aimed at preventing heat-related illnesses and fatalities. By understanding what a heat alert is, you can better prepare and take steps to protect yourself, your family, and vulnerable members of your community. To know more about advisory alerts, check out: Advisory Alerts: What They Are & Why You Should Pay Attention

How Are Heat Alerts Issued in Canada?

In the past, Canada employed a uniform threshold for heat alerts, applying the same criteria nationwide. However, this approach did not account for regional climate differences. What may be considered a heatwave in one area could be typical weather in another. Recognizing this, ECCC developed a more sophisticated system that defines heat alert criteria independently for 21 different regions. This tailored approach ensures that heat alerts are more accurate and relevant to local conditions.

The criteria for heat alerts are developed through a collaborative effort between health professionals and meteorological experts. These teams analyze data from past heat waves and assess their health impacts. This multidisciplinary approach ensures that the criteria for issuing heat alerts are scientifically sound and practically applicable. Check out our latest article on heat warnings to know more about it: Understanding Heat Warnings: Criteria, Updates, and the Role of Alertable

Key Factors That Trigger a Heat Alert

When ECCC evaluates whether to issue a heat alert, it considers a range of environmental and atmospheric conditions:

• Daytime Maximum Temperatures - Sustained high daytime temperatures can overwhelm the body’s ability to cool itself.
• Nighttime Minimum Temperatures - Warm nights prevent recovery from daytime heat, increasing health risks.
• Humidity Levels - High humidity makes it feel hotter than it is and intensifies heat stress.
• Local Geography - Urban heat islands, coastal climates, and elevation levels all influence when and where a heat alert is appropriate.

Regional Heat Alert Criteria Across Canada

Tailoring Heat Alerts to Local Conditions

Canada's diverse climate means that the definition and impact of heat waves can vary widely from one region to another. By tailoring heat alert criteria to specific regions, ECCC ensures that the alerts are relevant and actionable for residents. This approach increases the accuracy of heat alerts and enhances public compliance with recommended safety measures.

Local geography, such as proximity to water bodies, altitude, and urbanization, can significantly influence temperature and humidity levels. For instance, coastal regions may experience cooler temperatures due to sea breezes, while urban areas can suffer from the heat island effect, where buildings and pavement trap heat, significantly increasing the likelihood of heat waves. These factors are considered in the regional criteria for issuing heat alerts, making the warnings more precise and effective.

Examples of Heat Alert Thresholds by Region

• Southwest British Columbia - A heat alert is issued when daytime highs reach or exceed 29°C and nighttime lows stay above 16°C for two or more days.
• Essex and Chatham-Kent (Ontario) - A heat alert is triggered when the humidex hits 42 or higher for at least two consecutive days, reflecting the region’s higher tolerance to heat and humidity.

These examples show that what constitutes a heatwave in one part of the country may not be considered a heatwave in another, highlighting the importance of region-specific heat alerts.

Heat Alerts and Their Impact on Public Health

Research has shown that heat waves can lead to a range of health problems, from heat cramps and exhaustion to heat stroke and death. Vulnerable populations, including the elderly, infants, young children, and people with chronic illnesses, are particularly at risk during heat waves. For example, in 2018, a severe heatwave in Quebec led to over 70 deaths, and in 2021, more than 600 people died during a heatwave in British Columbia. These tragic events emphasize the need for accurate heat alerts and public awareness during extreme heat conditions.

Heat waves can lead to a range of health issues, from mild conditions like heat rash to severe illnesses such as heat exhaustion and heat stroke. Heat exhaustion is characterized by heavy sweating, weakness, dizziness, nausea, and headache. If not addressed, it can progress to heat stroke, a life-threatening condition marked by a high body temperature, confusion, loss of consciousness, and potential organ damage. Immediate medical attention is crucial in cases of heat stroke.

Long-Term Health Consequences of Heat 

Repeated exposure to heat waves, often signalled by heat alerts, can have long-term health effects, particularly for those with pre-existing conditions such as cardiovascular disease, respiratory issues, or diabetes. Chronic dehydration and electrolyte imbalances can also arise from prolonged periods of high temperatures, affecting kidney function and overall health.

How to Stay Safe During a Heat Alert

When a heat alert is issued, it’s essential to act quickly and follow safety guidelines to reduce the risk of heat-related illness or death. Both individuals and communities have a role to play in minimizing harm during extreme heat events.

Personal Safety Tips for Responding to a Heat Alert

Taking the right precautions during a heat alert can help you and your loved ones stay safe:

• Adjust Outdoor Activities - Avoid physical exertion during peak heat hours (usually 11 a.m. to 4 p.m.). Plan outdoor tasks for early morning or late evening.
• Seek Air-Conditioned Spaces - Spend time in air-conditioned buildings such as shopping malls, libraries, or designated cooling centers. Even a few hours can reduce your heat risk significantly.
• Stay Hydrated - Drink plenty of water throughout the day, even before you feel thirsty. Avoid alcohol, caffeine, and sugary drinks, which can dehydrate you.
• Check on Vulnerable Individuals - Older adults, infants, people with chronic health conditions, and those living alone are especially at risk during heat alerts. Make it a habit to check in on them frequently.
• Never Leave Children or Pets in Vehicles - Interior car temperatures can skyrocket in minutes. Always double-check before locking your vehicle.
• Use Fans and Cooling Techniques - Fans can help circulate air, and applying cool towels or ice packs to pulse points (like wrists or neck) can bring body temperatures down.
• Wear Light and Breathable Clothing - Choose loose-fitting, light-coloured clothes made of natural fabrics like cotton or linen.
• Limit Sun Exposure - Stick to shaded areas or wear a wide-brimmed hat and sunscreen to avoid direct sunlight and UV damage.

Community Actions During a Heat Alert

During a heat alert, communities can come together to provide essential support, especially for vulnerable populations:

• Set Up Cooling Centers - Municipalities can designate public buildings like schools, libraries, or community centers as cooling shelters open to the public.
• Distribute Water and Cooling Supplies - Local organizations, shelters, and businesses can help distribute bottled water, portable fans, and sunscreen to those in need.
• Launch Public Awareness Campaigns - Timely, accurate information about heat risks and protective steps should be shared via local news, radio, social media, and community bulletins.
• Support Vulnerable Neighbours - Community volunteers can help by checking in on elderly or disabled residents, offering rides to cooling centers, or delivering hydration supplies.

Stay Informed About Heat Alerts

Staying informed is one of the most effective ways to stay safe during a heat alert. Whether through digital tools or traditional media, timely updates can help you take immediate and appropriate action. Modern technology makes it easier than ever to stay ahead of severe weather events:

• Alertable App - The Alertable app, available for both iOS and Android, sends real-time heat alert notifications tailored to your location. It offers timely updates, public safety advice, and instructions from trusted sources, all in one place.
• Push Notifications & Alerts - Enable alerts on your smartphone to receive government-issued warnings, including heat alerts, even if you're not using an app.
• Smart Home Devices - Many smart speakers and home assistants can be configured to notify you of weather warnings, ensuring you stay informed without checking a screen.
• TV & Radio Broadcasts - Local stations often issue breaking news updates and emergency safety information when a heat alert is in effect.
• Local Public Health Websites - Municipal and provincial health departments often publish region-specific heat alert details, health guidance, and emergency resources.

Building Resilience During Heat Alerts

Resilience to extreme heat events doesn’t happen overnight—it requires planning, education, and community action. By improving infrastructure, increasing public awareness, and encouraging personal preparedness, communities and individuals can better withstand the impacts of a heat alert.

Heat Alerts and Urban Planning and Infrastructure

Urban design plays a crucial role in reducing the intensity and health impacts of heat waves:

• Increase Green Spaces - Parks, tree-lined streets, and rooftop gardens help cool cities naturally by providing shade and releasing moisture into the air.
• Reflective and Sustainable Building Materials - Using cool roofs, green walls, and materials that reflect sunlight can reduce indoor temperatures and energy usage during heat alerts.
• Water Features for Public Cooling - Installing spray parks, fountains, and misting stations in public areas provides immediate relief during extreme heat events.

These infrastructure choices help mitigate the urban heat island effect, reducing the likelihood and severity of heat alerts in densely populated areas.

Community Engagement and Education About Heat Alerts

Empowering communities with knowledge and resources can greatly improve outcomes during heat waves:

• Public Awareness Campaigns - Governments and health agencies can run seasonal campaigns to educate people on the dangers of heat and how to respond to a heat alert.
• School and Workplace Programs - Educational institutions and employers can integrate heat alert readiness into safety training and emergency planning.
• Partnering with Local Organizations - Collaborating with non-profits, libraries, and cultural centers can extend outreach to vulnerable and underserved populations.

Personal Preparedness for Heat Alerts

Taking proactive steps at the individual level can make a big difference:

• Create a Heat Alert Plan - Know where the nearest cooling center is, have transportation options ready, and identify who in your household or community may need extra help.
• Stock Emergency Supplies - Keep a supply of bottled water, electrolyte drinks, battery-powered fans, and basic first aid materials on hand. Check out our detailed article on how to make an emergency kit: 72-Hour Emergency Kits: The Ultimate Guide to Emergency Preparedness
• Know the Signs of Heat Illness - Being able to recognize and respond to symptoms of heat exhaustion and heat stroke is critical during a heat alert.

The Importance of Heat Alerts

Heat alerts are more than just weather warnings—they are essential public health tools that save lives. As climate change continues to increase the frequency and intensity of heat waves across Canada, it’s more important than ever to understand what heat alerts mean and how to respond effectively.

By recognizing the signs of heat-related illness, adapting your daily routines, and looking out for vulnerable members of your community, you can reduce the health risks associated with extreme heat. Proactive urban planning, community support systems, and individual preparedness all contribute to building resilience during heat events.

For up-to-date and localized heat alert notifications, download the Alertable App—your trusted source for public safety alerts in Canada. You can also visit Environment and Climate Change Canada’s website for official updates and resources.

Stay cool. Stay informed. Stay safe.