On August 15th 2021 it was 23.9°C at the Peterborough Municipal Airport. By all respects, an average summer temperature. If you looked at a thermometer outside your house though, it might paint a much different picture. In the downtown core and areas along Lansdowne St. temperatures reached as high as 40°C. This represents over 15°C temperature difference! What is happening and how can it be stopped?
The urban heat island is a phenomenon we’ve long known about. It occurs when natural land cover such as forest or meadows are replaced with surfaces that retain heat such as asphalt, concrete or pavement. These surfaces then radiate the heat back out into the local environment, warming the surrounding area. The effect can increase the cost of heating, and put elderly or other vulnerable citizens at risk of heat stroke, and even death.
The urban heat island effect often puts the most vulnerable populations at risk. Some of Peterborough’s lowest income census areas have the highest recorded temperatures. You’ll notice on the map that areas directly south and north of the downtown which are characteristic as lower income neighborhoods, have some of the highest recorded temperatures, while some of Peterborough’s more affluent neighborhoods have much lower recorded temperatures.
Image #1 characterizes a neighborhood south of downtown. Census Canada considers between 35% and 43% of the population to be low income. This neighborhood is one of the hottest in Peterborough, coming in at a 15°C temperature deviation. Meanwhile Monaghan Ward represented in image #2 only recorded a 5°C temperature deviation. It is clear that land cover and tree canopy have a huge impact on temperature deviation. With the additional pressure of climate change, these deviations are likely to become more pronounced over time.
What can be done about urban heat though? Luckily we have some solutions! Planting trees is once again, a major winner in this regard. Not only does tree planting decrease average temperatures, it can lower heating and cooling bills year round for residents, overall a huge win for the climate. Removing asphalt and other “high heat” surfaces can also benefit neighborhoods, replacing asphalt with grass is even a viable solution for combating urban heat. Depave projects around the country have made major inroads in this regard, and perhaps focusing on lower income neighborhoods could have an additional impact.
In all, reducing the urban heat island effect gives us one more incentive to restore ecosystems, plant trees, and protect our natural areas. Perhaps years from now, when you look at the thermometer outside your house, it may more accurately reflect the temperature across our city.
Data provided by USGS through LANDSAT 8.