Cities warm up ‘like stones in a sauna’ during a heat wave. Can that change?

Many parts of Canada continue to face a protracted heat wave, with “dangerously hot and humid” conditions persisting through much of southern Ontario and parts of Quebec.

Experts say city and suburb dwellers have it much worse than their counterparts living in the countryside due to a phenomenon sometimes referred to as ‘urban heat island effect.”

Many are cautioning that cities need to urgently adapt to warming summers as extreme heat becomes more common.

The Climate Atlas of Canada says the urban heat island phenomenon happens when paved surfaces amplify and trap heat far more effectively than natural ecosystems and rural areas. On a sunny day, paved surfaces can be 27 to 50 °C hotter than the air, the Climate Atlas says.

“The concrete and asphalt surfaces in urban areas act like the hot stones in a sauna, if you will. They absorb the incoming solar radiation, turn it into heat, and rebroadcast it out,” Ryan Ness, adaptation research director at the Canadian Climate Institute, told Global News.

Ness said the difference can be even more pronounced at night, with cities and suburbs being up to 10 to 12 degrees warmer than rural areas. Data shows that Canadian cities are going to get a lot warmer.

According to the Climate Atlas, between 2051 and 2080, Canadian cities will see at least four times as many days with temperatures higher than 30 C.

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Ness said this shows the need to adapt cities urgently.

“(Cities need to have) emergency response capacity ready to go, ambulances, emergency rooms, emergency cooling shelters for people who don’t have air conditioning in, check-up programs for elderly people who live alone,” he said.

Caroline Metz from the Intact Centre on Climate Adaptation at the University of Waterloo, said of the 617 deaths caused by the 2021 B.C. heat dome, 98 per cent of the fatalities were seniors.

Metz said some cities in Canada are already trying to adapt.

“Some cities are even piloting using reflective pavements to reflect solar radiation on streets. Painting roofs white is being widely embraced,” she said.

Painting flat roofs white can help reflect the heat back, instead of absorbing it.

Ness said adding trees and green space to a cityscape can help too.

“Those of us who live in the Greater Toronto Area will know, there’s hundreds of square kilometres of suburbs with very little tree cover. The land was scraped clean of its topsoil so it could be graded and engineered for subdivisions,” he said, adding that “car-dependent cities are often hotter because they have more asphalt.”

A 2021 report by the Canadian Energy Systems Analysis Research, also known as CESAR, said Canada has exponentially more parking spaces than cars. The report said Canada has around 23 million light-duty vehicles but has somewhere between 71 million to 97 million parking spots.

That suggests there are 3.2 to 4.4 parking spots for every car in the country.

In some cities, parking takes up most of the space in the city’s downtown core.

In Regina, for example, nearly half of private land in the city’s downtown core is parking lots.

Ness said in the short term, adding shade, trees and rebuilding urban forests can help. In the long-term, he said cities must build capacity for car-free commuting.

“Using active transportation, where we’re walking and biking, really contributes to that overall effect of reducing heat and reducing our emissions,” Metz said, adding that a reduced dependency on cars also means fewer paved surfaces overall.

Ness said that along with building urban forests, cities also need to become more compact so that suburban heat islands don’t keep growing.

“We need to be designing dense cities, so that there are opportunities for people who no longer have yards to get outside, to have parks, to have well-designed and welcoming outdoor spaces, so that it doesn’t feel like a sacrifice to live in a condo or townhouse rather than a detached house in the suburbs,” he said.