Ottawa in 2050: Extreme heat

Climate change means warmer seasons, more days over 30 degrees Celsius, high humidex and risk of drought. The top risks from extreme heat are dehydration, heat exhaustion and stroke, stressed natural and agricultural areas, limited shared areas and places to cool off, limited air conditioning and too hot for walking, cycling and outdoor activity.

Ottawa’s climate is already getting warmer. Between the mid-1940s and the mid-2010s the average temperature in Ottawa increased by 1.3 degrees Celsius.

This trend will continue in the future. Ottawa will be warmer year round, there will be more extreme heat days and less extreme cold days.

What we are expecting

By the 2050s, under a high-emission scenario, temperature in the National Capital Region is projected to change in the following ways.

  • Increase in average temperatures in all seasons – the average temperature will increase by 3.2 degrees Celsius.
  • Less cold extremes – the number of days below -10 degrees Celsius will decrease by 35 per cent. That’s a decrease to 46 days per year from the current 71 days.
  • More warm extremes there will be four times as many very hot days over 30 degrees Celsius. That’s an increase to 43 days per year from the current 11 days.
  • Increase in humidex – the number of days with high humidex levels will increase.
  • Drought – more variability in precipitation and risk of drought

You can find out more details of what to expect in the 2030s and 2080s in the Summary of the Future Climate in Canada’s Capital Region.

What are the top risks from extreme heat and drought?

  • Increased heat-related illnesses – extreme heat can cause dehydration, heat exhaustion, heat stroke and even death.
  • Less outdoor recreation and active transportation – hotter and more humid summers could lead to a decrease in outdoor recreation and sports and the cancellation of community events.
  • Increased need for cooling in buildings – as temperatures rise, there will be more demand for cooling in the summer which will increase energy costs. Buildings may also need to be retrofitted to add better cooling and ventilation. Community buildings such as churches, daycares or schools may be forced to close temporarily during extreme heat events if they do not have adequate air conditioning.
  • Increased demand for shaded areas and indoor and outdoor recreation facilities to offset heat
  • Impacts on the natural environment – extreme heat and drought place additional stress on our ecosystems. Algal blooms are harmful to human health and will cause no swim advisories.
  • Reduced agricultural yields and increased irrigation – extreme heat and drought create challenging growing conditions and reduce harvest.

More information about the climate impacts facing Ottawa is available in the Climate Vulnerability and Risk Assessment.

Who is most vulnerable to extreme heat?

High temperatures can put everyone at risk, especially those without access to air conditioning. Health risks are greatest for infants, older adults, people who work or exercise outdoors, those with pre-existing health conditions, and people experiencing homelessness.

Reduced access to recreation could impact the mental health and wellness of individuals and families who could find themselves even more isolated if free/low-cost outdoor activities are cancelled.

How can you prepare?

We all have a role to play in preparing for the impacts of changing weather patterns and extreme events. Find out what you can do, what the City is doing and visit the Resource Hub (coming soon) where we have additional resources that can help communities prepare for climate change.

The Urban Heat Island Effect

This is a map of the City of Ottawa which is colour coded in increments to show land surface temperature. This map shows that rivers, lakes, greenspaces, parks, natural spaces and light-coloured surfaces (e.g. white roofs) tend to be cooler. Large buildings with dark roofs (e.g. commercial, institutions), large parking lots and artificial turf absorb and retain heat. These areas are referred to as urban heat islands.

The urban heat island effect occurs when built-up areas are hotter than surrounding areas. Buildings, parking lots and other dark surfaces retain heat and become hotter than nearby greenspaces, water and rural areas. The annual mean air temperature of a city with one million people or more can be one to three degrees Celsius warmer than its surroundings during the day. In the evening, the difference can be as high as 12 degrees Celsius.

The City of Ottawa in partnership with Ottawa Public Health created two urban heat island maps using satellite imagery from July 18, 2019, a hot day where temperatures reached 27.3 degrees Celsius and the humidex reached 31:

The colour codes show how surface temperatures ranged from 15 to 38 degrees Celsius across the City. The map shows cooler areas include the Ottawa and Rideau Rivers and their tributaries; the Greenbelt; greenspaces, parks, natural spaces; and light-coloured surfaces including buildings with white roofs. Buildings with dark roofs, such as those found on large commercial and institutional buildings, parking lots and artificial turf show up as hotter areas that absorb and retain heat.

These maps highlight areas of potential additional risk created by the urban heat island effect. Additional factors that influence an individual’s risk include access to air conditioning at work, school, home and during commutes, if they work or exercise outdoors, their age, and pre-existing health conditions.

How are these Urban Heat Island Maps being used?

Heat island maps show us how land use choices affect surface temperature. With temperatures expected to rise by 3.2 degrees Celsius by the 2050s and the number of days above 30 degrees Celsius expected to rise fourfold to 43 days, heat islands worsen the impact of extreme heat events. Extreme heat affects everyone, but certain people are more vulnerable to heat stress, including the very young and old, people who are pregnant, people with existing health conditions, people who work outside, athletes, people who are homeless or precariously housed, and those that don’t have good access to air conditioning.

Heat island maps can be used to guide policies and planning of the built environment. Strategies to reduce surface temperatures include tree protection and plantings, the use of vegetation on and around buildings and parking lots, and the inclusion of parks and greenspace and reflective surfaces such as light-coloured roofs.

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