Statistics Canada’s first study of green spaces in cities shows that cities across the country are getting grayer and browner.
Posted at 6:07 p.m.
“We have seen a decrease (in green spaces) over the study period,” said Jennie Wang, who helped prepare a major federal agency report released this month on human activity. and the environment.
Statistics Canada used satellite images to estimate the amount of green space in Canadian cities, including parks, trees, backyards and lawns. The data has existed for years, but was used to carry out this study.
Researchers looked at 31 urban centers of varying sizes across the country. They compared satellite images from 2001, 2011 and 2019.
They found that around three-quarters of large and medium-sized cities were less green in 2019 than they were 20 years earlier.
The big losers include cities like Kelowna, British Columbia, which fell from nearly three-quarters of green space to less than half. The city of Milton, Ont., saw a similar decline, as did Winnipeg.
Toronto, Montreal, Vancouver, Calgary and Edmonton all lost green space. Saskatoon and Regina were among the few cities to win.
According to Mme Wang, urbanization is an important factor in the loss of vegetation in cities. Milton, Ontario grew by 350% over the study period, and Kelowna’s population grew from 150,000 to 223,000.
Other factors, such as drought or insect infestations, also play a role. Winnipeg’s loss of green space, for example, has been exacerbated by the emerald ash borer.
According to Mme Wang, the loss of these spaces is significant and has real consequences.
“There have been studies showing the many benefits of vegetation,” said Ms.me Wang. There are reductions in energy consumption, trees remove air pollutants. There are also human health benefits. »
Green spaces also reduce what are called urban heat islands – high temperature bubbles around cities.
A University of Alberta geographer and urban planner, Sandeep Agrawal, has found that the temperature difference between a city like Edmonton and the surrounding countryside can be as much as five or six degrees. This differential is linked to the quantity of green spaces in urban centres.
“If tree cover decreases, the urban heat island effect increases a bit,” Agrawal explained.
Heat islands can contribute to human health issues like respiratory failure or heat stroke, a problem made worse by heat waves like the one experienced last summer across much of Western Canada.
The British Columbia Coroner’s Office recorded 569 deaths related to this issue between June 20 and July 29.
Mr. Agrawal said there is no turning back once a pasture or woodlot has been razed to make way for houses or shopping malls. Even when landscaping matures, it does not completely replace what was there before.
“You can never do that,” he said. It’s just not possible. »
Governments are beginning to recognize the problem, he says, making it more difficult to cut trees on public lands and enacting laws promoting “green roofs”, i.e. vegetation planted on top of buildings. .
Most Canadians live in cities, said Ms.me Wang. She added that her research can help governments understand how their policies affect the trees and grass that grow alongside concrete and asphalt in cities.
“This kind of information can help cities monitor whether their policies have had an effect. “, estimated M.me Wang.