The urban heat island effect occurs when built-up areas are hotter than surrounding areas. Buildings, parking lots and other dark surfaces in built-up areas 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 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