In mid-summer 2019, Ottawa melted during a withering heat wave.
On July 18, Environment Canada issued a heat warning, and Ottawa Public Health advised residents to stay hydrated and check on vulnerable neighbors.
According to historical weather data, the temperature on Thursday approached 28 C, and it felt like 31 degrees with the humidity, but certain areas of the city were significantly warmer – as much as 10 degrees Celsius warmer in some places.
A map produced by the city and public health shows exactly where these hot spots were – and where they remain today.
Using satellite imagery, the color-coded map shows a wide range of surface temperatures recorded that day, from 15 C along sections of the Ottawa River to between 36 and 38 C in certain small pockets of the city, where both water and vegetation are, in short, supply.
These pockets appear on the map as red dots surrounded by brown, yellow and other shades representing slightly cooler temperatures. The coolest areas are shown on the map in shades of green and blue.
Lots of asphalt, few trees
One of the red zones is the Carlingwood Shopping Center, where the former Sears store was demolished just three months before the satellite image was taken, and its surrounding parking lot.
Even on a clear October day, it’s easy to see why: the mall’s expansive roof is flat and dark in color, it’s surrounded by acres of asphalt, and unlike nearby residential neighborhoods, there is virtually no vegetation that can help absorb the heat or protect customers from the glare of the sun. This is the urban heat island effect in action.
“The surface temperature range is pretty amazing,” said Robb Barnes, CEO of Ecology Ottawa, who got his first good look at the map earlier this month. “We know the urban heat island effect is pronounced, but I did not know it would be so extreme.”
Only a handful of other areas reached the same surface temperature as Carlingwood on July 18, 2019, all at the city’s east end: St. Laurent Shopping Center, OC Transpo headquarters on St. Laurent Boulevard, an industrial park near the Canada Science and Technology Museum and pockets near the Giant Tiger on Walkley Road.
They all share common characteristics with Carlingwood: massive buildings with flat roofs, large surface parking lots and little or no greenery.
Maps are ‘powerful tools’
These heat maps can also tell a different story, Barnes said: They can expose the problem of housing inequality by demonstrating that richer neighborhoods tend to be greener than poorer and therefore more comfortable for the people who live there.
“Maps are such powerful tools for conveying that information,” Barnes said. “There’s so much you can do with that kind of map data that would really help draw a picture of what’s needed in Ottawa and what are the opportunities to improve our city.”
An obvious solution is to plant more trees to breathe some life into the barren spaces.
The city’s draft official plan sets a long-term target for tree canopies in the cities of 40 percent, an ambitious target given that only about a quarter of Ottawa’s urban landscape is currently shaded by trees. (A separate assessment of tree crowns by the metropolitan area in the fall of 2019 estimated Ottawa’s coverage at 31 percent.)
Looking at maps like these reveals where these trees are most needed, according to Jennifer Court, CEO of the Green Infrastructure Ontario Coalition.
“For people who live in urban areas and experience the effects of urban heat, it helps to put a visual representation of something that they have lived experience with,” she said.
Court also mentioned green roofs and permeable parking lots as other potential solutions to cool the hot spots that the map shows.
She said the maps are also useful tools to help cities shape social policies and make decisions, such as where to open cold stores when temperatures rise to dangerous levels.
“Seeing a map like this and understanding what parts of the city nearby can … offer some relief can be a real help and can be a real lifesaver,” she said.
According to the city, average temperatures in Ottawa are expected to rise by 3.2 degrees Celsius over the next three decades, and the average number of days above 30 C will quadruple to 43 per year. Vulnerable residents, including the very young and old, pregnant women, people with pre-existing health conditions, people working outside and people experiencing homelessness are most at risk when temperatures rise.
“Heat Island maps can be used to guide policies and planning the built environment,” the city said on its website.
Barnes said Ecology Ottawa and other groups plan to pressure the city to make it a priority during upcoming discussions on Ottawa’s official plan.