Toronto is recovering in the aftermath of heavy rains and flash floods that wreaked havoc across the region Tuesday night, showing the city’s aging sewer system’s vulnerability to sudden, extreme weather conditions.
Some parts of the city saw 100 millimetres of rainfall in less than two hours during Tuesday’s storm, according to Jennifer Drake, an assistant professor in the department of civil and mineral engineering at the University of Toronto.
Major intersections across the city were submerged underwater late on Tuesday night, from Bloor Street and Dufferin Street in the west end, to Bathurst Street and Lake Shore Boulevard in the south. The effects rippled into Wednesday, with the Toronto Transit Commission forced to suspend subway service for the day on a portion of Line 1 owing to flooding at Sheppard West station, and Toronto Hydro reporting several power outages throughout the day, mainly in buildings just to the west of the Don Valley Parkway.
“It was a large amount of rainfall in a very short amount of time,” Dr. Drake said. The intensity of the storm, she said, is on par with some of the most extreme storms Ontario has ever seen, such as Hurricane Hazel in 1954, which saw a peak two-hour rainfall intensity of 80 to 100 millimetres.
A combination of an extreme weather event and the city’s decades-old sewer system exacerbated the level of flooding. And while Tuesday’s storm was rare, it’s expected there will be more in the coming years because of the effects of climate change.
The general consensus among scientists, Dr. Drake said, is that Ontario will have more frequent, intense isolated storms. She added that rain events of the size seen on Tuesday exceed the design capacity of the city’s infrastructure, which is why flash floods occurred across Toronto. “We don’t build our pipes that big to handle that much water,” Dr. Drake said.
Mayor John Tory told reporters at a campaign event in Scarborough on Wednesday that Toronto is committed to funding stormwater projects. He said the city’s water department is investing hundreds of millions of dollars in a “robust plan” for flood mitigation and stormwater sewer improvements, some of it prompted by warnings that climate change is creating more severe weather.
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