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Extreme heat


Extreme heat

The term "heat wave” refers to a period of extreme heat that lasts for several days and nights. The thermal characterization of a heat wave is subjective, as it depends on the sensitivity of populations and thus, on the location of the heat wave. In Montréal, a heat wave is considered to be two consecutive nights where the temperature is higher than 25°C and three consecutive days where the temperature is higher than 33 °C.

A number of climate studies predict weather conditions that are likely to increase the frequency and intensity of heat waves, which is why preparing yourself is especially important.  

Preparing and protecting yourself

Risks in Montreal

A number of heat waves have hit Western countries over the past few years, and Montréal has not been spared. In Montréal, public health authorities estimate that an extreme heat wave could have especially severe health implications. The Montreal agglomeration, in collaboration with the local health and social services agency CIUSSS du Centre-Sud de l'Île-de-Montréal, has developed a special response plan for heat waves to minimize impact on the population. This plan was activated in July 2010, 2011 and 2018, when, over a period of several days, temperatures were higher than 33°C in the city

Impacts on the population and those at risk

  • Direct effects: cramps, fainting, dehydration, exhaustion and heat stroke
  • Indirect effects: more frequent than direct effects, worsening of another illness or fragile health in vulnerable personsé

Direct and indirect effects can lead to an increase in medical consultations, hospitalizations and deaths.

Other potential impacts:

  • Increased demand for residential drinking water, affecting the capacity to produce drinking water.
  • Lowered water levels in bodies of water around the Montréal agglomeration, which could affect water quality and changes to the way water is treated in treatment plants.
  • Sudden, violent storms causing heavy rain, strong wind, hail and tornadoes.
  • Massive deaths in a short period of time.

At-risk persons in extreme heat:

  • Seniors: People 65 and over living in dwellings without air conditioning.
  • People with chronic illnesses: Cardiovascular, cerebrovascular, respiratory, renal and neurological illnesses; diabetes.
  • Patients on diuretic, psychotropic or anticholinergic medications, or tranquilizers.
  • Infants and small children (0-4 years)
  • People who live in urban heat islands
  • People with diminishing abilities who live alone
  • Workers and athletes who do physically demanding work

Source : Chaleur accablante ou extrême 2019 - Plan régional de prévention et de protection et Guide à l'intention des établissement de santé, CIUSSS CSMTL, 2019 (in French only)

Extreme heat special response plan

The extreme heat special response plan was created in 2003 following events in France. It was implemented for the first time in July 2010 after a heat wave struck southern Québec.

Important Numbers

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