Extreme Heat

Climate change is increasing the frequency, duration, and intensity of the number of very hot days over 30°C in Canada. During heatwaves, the daytime and night-time average temperatures are projected to increase almost everywhere across the country, and will become longer, hotter and more common than heatwaves experienced in the past. Exposure to extreme heat will be most pronounced in three areas: low-lying areas in B.C. from the West Coast to the Rocky Mountains; the southern Prairies, including Alberta, Saskatchewan and Manitoba; and southern Ontario and Quebec. In cities, these extreme heat events can be exacerbated by urban heat islands, which occur due to heat-absorbing building surfaces and materials and the lack of greenspace or tree canopies. Urban heat islands elevate temperatures in cities compared with surrounding rural areas and amplify heat-related health impacts. Rural areas also suffer from heat-related effects but face distinct challenges in responding to extreme heat compared with urban centers.

The health impacts of extreme heat range from mild to life-threatening, depending on individual susceptibility, duration, and exposure. The symptoms of extreme heat exposure include heat rash, edema, cramps, and exhaustion. These symptoms can lead to heat stroke (loss of consciousness and death) or exacerbation of chronic cardiac or respiratory illnesses. Those most susceptible to extreme heat include seniors, people who are socially isolated or who live alone, and people who have low income. Some chronic conditions can also put people at higher risk, especially severe mental illness, substance use disorder, diabetes, heart disease, and respiratory disease. Some specific mediations and illicit drugs are known to interfere with thermoregulation, such as antipsychotics and cocaine. In areas where extreme heat is expected, effective communication with the public before and during events to convey the health risks and protective actions is essential to ensuring safety and wellbeing.

This topic pages aims to provide a list of curated resources on preparing for and responding to extreme heat events. The first section lists resources directed at individuals, households and communities, while the second section lists resources directed at public health professionals and policy-makers. Lastly, resources on risk communication for extreme heat events are also shared.

Resources for individuals, households and communities

• Irreversible extreme heat: protecting Canadians and communities from a lethal future (Intact Centre on Climate Adaptation, 2022)
  This guide outlines a series of actions individuals, property owners and managers, and communities can take to mitigate the risks of extreme heat events. Actions are divided into three categories: 1) planning and behavioural changes, 2) working with nature, and 3) improving buildings and public infrastructure.

• Extreme heat preparedness guide (Prepared BC, 2022)
  This guide provides advice for individuals to prepare and respond to an extreme heat emergency, including step by step instructions on developing an emergency plan, when to activate the plan, and tips for staying cool both inside and outside.

• Preventing injuries and deaths during extreme heat events (NCCEH, 2022)
  This upcoming webinar will review the effects of the 2021 heat dome in BC and examine how individuals and communities can mobilize to improve our preparedness to respond and adapt to extreme heat events and protect those most susceptible during extreme hot weather.

• Reducing the health effects of hot weather and heat extremes: from personal cooling strategies to green cities (Jay et al., 2021)
  This peer-reviewed article describes several accessible and sustainable interventions to reduce the risks of extreme heat and explores the barriers and opportunities for the implementation of these solutions in settings such as long-term care homes, workplaces, schools and mass gatherings. 

• Climate Atlas of Canada (2019)
  This mapping tool allows users to zoom in on their region of interest and observe how climate change is predicted to affect the average number of very hot days (days over 30C) in a year, both in the near term (2021-2050) and in the long term (2051-2080).

• Extreme Heat can be a Killer (NCCEH, 2018)
  This videoprovides an overview of the rising temperatures in BC cities, the associated mortalities in various Canadian provinces, the vulnerable populations most likely to be affected by extreme heat events, and also highlights some interventions and the importance of extreme heat plans to protect people's health. 

Resources for public health professionals and policy-makers

• Extreme heat: Heat Alert and Response Systems (HARS) across Canada (Health Canada, 2022)
  This webpage provides basic information on Heat Alert and Response Systems in Canada, including a useful figure illustrating the different components of a community HARS with preventative actions to reduce heat-health risks.

• Analysis of community deaths during the catastrophic 2021 heat dome (Henderson et al., 2022)
  This peer reviewed article analyzed data from the 2021 heat dome in British Columbia and found that deprivation and lower neighbourhood greenness were most predictive of risk of death. Implications for public health response are outlined.

• Extreme heat and human health: For pharmacists and pharmacist technicians (Health Canada, 2021)
  This document provides information for pharmacists and pharmacist technicians during extreme heat events, including common medications that can exacerbate heat-related illnesses, and key resources to share with patients who are prescribe these medications.

• Canada in a changing climate: national issues report (Government of Canada, 2021)
  This chapter discusses the impact of climate change on Canada’s cities and towns, and provides examples of adaption strategies that have been implemented to mitigate these impacts, including those targeted at addressing extreme heat events in urban areas.

• Large model structural uncertainty in global projections of uban heat waves (Zheng et al. 2021)
  This peer reviewed article looks at how urban heat waves are predicted and demonstrates that uncertainty in the modelling techniques used show that heat risk could be underestimated, suggesting that planners and policy makers will need to account for this uncertainty in their heat response plans.

• Social connection as a public health adaptation to extreme heat events (Kafeety et al., 2020)
  This commentary outlines how social connection can help protect those at greatest risk during extreme heat events and suggests several strategies public health agencies and their partners should consider to foster greater social connection at the community level.

• Reducing urban heat islands to protect health in Canada (Health Canada, 2020)
  This report provides tips, strategies and case studies to help public health professionals support local governments and organizations to reduce urban heat islands in Canada, with advice focused on outdoor air temperatures in particular.

• Developing a harmonized heat warning and information system for Ontario: a case study in collaboration (Henderson et al., 2020)
  This peer-reviewed article describes the process in developing a harmonized heat warning and information system for Ontario, and the key lessons learned.

• Developing a municipal heat response plan: a guide for medium-sized municipalities(BCCDC, 2017)
  This document provides best practices for how to integrate heat preparedness into existing emergency plans for communities with fewer resources.

• Cities adapt to extreme heat: celebrating local leadership(Institute for Catastrophic Loss Reduction, 2016)
  This book gives case studies of municipalities which are completing projects to adapt to the risks of extreme heat, including: issuing targeted warnings; opening cooling centres in public facilities such as libraries, community centres and public pools; providing water for those in need; educating the public; and actions to reduce urban heat islands, such as planting trees.

• A difference-in-differences approach to assess the effect of a heat action plan on heat-related mortality, and differences in effectiveness according to sex, age, and socioeconomic status (Montreal, Quebec)(Benmarhnia et al., 2016)
  This academic article examines the effectiveness of heat action plans, which were shown to reduce heat-related mortality in vulnerable populations in Montreal, Canada.

• Approaches for building community resilience to extreme heat(Berry et al., 2016)
  This book chapter outlines the state of knowledge of development of Heat Alert and Response Systems (HARS) in Canada, social determinants of health which may impact citizens, government and community stakeholders who must be engaged in the process, and case studies of capacity building in at risk communities.

• Heat alert and response systems to protect health: best practices guidebook (Health Canada, 2011)
  This guidebook describes evidence-based strategies for alerting health authorities and the public when dangerous conditions arise.

Best practices for communicating the risks of extreme heat

• Global heat health information network: Communicate and advocate (Global Heat Health Information Network, 2021)
  This webpage produced by an international, interdisciplinary team of extreme heat experts and policy makers, provides numerous resources and other learning opportunities, including a range of risk communication, awareness and advocacy strategies and outreach materials.

• Communicating heat risk: Experiences from C40’s cool cities network (C40 Knowledge Hub, 2020)
  This report provides guidance on communication strategies for reaching different heat-vulnerable groups, examples of heat communication best practices, and considerations for risk communication during the COVID-19 pandemic.

• Reducing the risks of extreme heat for seniors: Communicating risks and building resilience (Eady et al., 2020)
  This peer reviewed article examined the risk perceptions and coping practices of seniors in the Waterloo Region to extreme heat events and found vulnerability to be more strongly correlated with social connection and access to resources than inaccurate risk perception.

• Communicating the health risks of extreme heat events: toolkit for public health and emergency management officials (Health Canada, 2011)
  This toolkit provides guidance on the best communication practices for addressing health risks from extreme heat, based on experience gathered both nationally and internationally.

This list is not intended to be exhaustive. Omission of a resource does not preclude it from having value.