What is the Urban Heat Island Effect?
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 a day where temperatures reached 27.3 degrees Celsius and the humidex reached 31:
- Map showing temperature differences for Ottawa
- Map showing temperature differences within Ottawa’s Greenbelt
The colour codes show how surface temperatures ranged from 15 to 38 degrees Celsius across the City. The map shows cool 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 hot areas that absorb and retain heat.
These maps highlight areas of potential 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.
Find out more about urban heat islands:
- Health and the Built Environment - Ottawa Public Health
- Reducing urban heat islands to protect health in Canada
- How Health Canada is collaborating with Canadian communities to reduce the urban heat island effect
- Does urban vegetation reduce temperature and air pollution concentrations? Findings from an environmental monitoring study of the Central Experimental Farm in Ottawa, Canada