By Bob Weber
THE CANADIAN PRESS
Joni Mitchell was right 鈥� they really are paving paradise and putting up parking lots.
Statistics Canada鈥檚 first survey of urban green space shows that, just as the singer-songwriter warned, cities across the country are getting greyer and browner.
鈥淲e did a see a decrease over the time period we looked at,鈥� said Jennie Wang, who helped prepare a massive report from the federal agency released this month on human activity and the environment.
StatCan used satellite imagery to estimate the amount of green space in Canadian cities 鈥� parks, urban trees, even backyards and lawns. The data has existed for years, but it was used for this purpose.
鈥�(We鈥檙e) getting a sense of the condition of vegetation in urban areas,鈥� Wang said. 鈥淚t鈥檚 the first time we鈥檝e done that.鈥�
The researchers looked at 31 urban centres of various sizes across the country. They compared satellite images from 2001, 2011 and 2019.
They found about three-quarters of large and medium-sized cities were less green in 2019 than they had been 20 years earlier.
鈥淵ou end up seeing less green as you walk down the street,鈥� Wang said.
Big losers include cities such as 麻豆精选, which went from nearly three-quarters green to less than half. Milton, Ont., went through a similar drop, as did Winnipeg.
Toronto, Montreal, Vancouver, Calgary and Edmonton all lost green space. Saskatoon and Regina were among the few that gained.
Urbanization is a big driver of green space loss, said Wang. Milton grew by 350 per cent over the course of the study and 麻豆精选鈥檚 population grew from 150,000 to 223,000.
Other factors such as drought or insect infestations also play a role. Winnipeg鈥檚 losses, for example, were exaggerated by the emerald ash borer.
But the losses are real, said Wang, and have real implications.
鈥淭here鈥檚 been studies showing the many benefits of vegetation,鈥� Wang said. 鈥淭here鈥檚 reductions in energy use, trees remove air pollutants. 鈥淭here鈥檚 also research looking into human health benefits.鈥�
Green spaces also reduce what鈥檚 called urban heat islands 鈥� bubbles of high temperature around cities.
Sandeep Agrawal, a geographer and urban planner at the University of Alberta, has found the temperature difference between a city such as Edmonton and the surrounding countryside can be as high as five or six degrees. That differential is linked with the amount of urban green.
鈥淚f the tree cover goes down, the urban heat island effect goes up quite a bit,鈥� he said.
Heat islands can help cause human health problems such as respiratory failure or heat stroke, a problem worsened in heat waves such as that experienced last summer over much of Western Canada.
The B.C. coroner鈥檚 office identified 569 heat-related deaths between June 20 and July 29.
There鈥檚 no going back once a pasture or woodlot has been bulldozed for houses or shopping malls, Agrawal said. Even when the landscaping matures, it doesn鈥檛 fully replace was what there before.
鈥淵ou can never do that,鈥� he said. 鈥淚t鈥檚 just not possible.鈥�
Governments are starting to recognize the issue, he said, making it tougher to cut trees on public land and enacting laws promoting so-called 鈥済reen roofs,鈥� vegetation planted atop buildings.
Most Canadians live in cities, Wang said. She said her research can help governments figure out how their policies are affecting the trees and grass that live alongside the urban concrete and asphalt.
鈥淭his kind of information can help cities monitor whether there鈥檚 been an effect from their policies.鈥�
This report by The Canadian Press was first published Feb. 1, 2022.
鈥� Follow Bob Weber on Twitter at 鈫時ow1960
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