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Police officers look on as water floods King St. W. during heavy rain, stopping a streetcar in Toronto on Tuesday, August 7, 2018.Shlomi Amiga/The Canadian Press

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.

Related: Just inches of air left for two men rescued from flooded elevator

“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.

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Cars drive along a flooded street in Toronto, Ontario, Canada August 7, 2018 in this still image taken from video obtained from social media. Narmin/via REUTERS THIS IMAGE HAS BEEN SUPPLIED BY A THIRD PARTY. MANDATORY CREDIT. NO RESALES. NO ARCHIVES.SOCIAL MEDIA/Reuters

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.

Critics of Mr. Tory, however, pointed to his move to shelve a proposed fee last year that would have taxed landowners on hard surfaces, such as parking lots, on their property, because these types of surfaces are most responsible for rain and snow runoff.

The money from the tax would have been used for stormwater sewer improvements. Cities in the Greater Toronto Area, including Aurora, Markham, Mississauga and Richmond Hill, have one in place, as do Ottawa, Kitchener and London.

Councillor Mike Layton argued in favour of a stormwater tax and said it encourages large property owners to reduce the amount of runoff from their properties, which would help the city’s sewers handle storms. “There [would be] an incentive there for them to go and reduce the amount of stormwater they produce," Mr. Layton said in an interview.

Dr. Drake said a stormwater utility charge “should be revisited by the city," as it encourages home and commercial property owners to invest in infrastructure on their land that can help the city manage stormwater. It would also create revenue for continuing infrastructure projects to mitigate the effects of extreme weather conditions across the city.

Mr. Tory said all of the city’s water projects were proceeding without the proposed fee and not “one penny” had been removed from the budget for such projects.

“The fact is, all of the projects that are extensive in number and extensive in millions of dollars in investment, are proceeding,” Mr. Tory said. “Not one of them has been slowed down or delayed or postponed or cancelled or not proceeded with because of lack of money. They are all budgeted. It was simply a different way of collecting the money.” But Mr. Tory did acknowledge that the fee was still up for discussion.

The City of Toronto has several stormwater infrastructure projects included in a 10-year plan, in which $3.1-billion has been allocated for stormwater management, with it being split between a Basement Flooding Protection Program to improve sewer capacity and a Wet Weather Flow Master Plan to improve stormwater quality that is released to the city’s waterways and Lake Ontario, according to Toronto Water manager Frank Quarisa.

Transit projects have also lent a helping hand with improving infrastructure in the city. Anne Marie Aikins, a spokesperson for Metrolinx, said several unfinished projects, including the Crosstown LRT along Eglinton, have been instrumental in helping to replace the city’s aging sewer system.

“I think there’s always more work to be done, but what I’ve seen is improvement over the last five years because people have been very committed," Ms. Aikins said of replacements to the sewer system aided by transit projects. "They recognize [that] extreme weather is real.”

With files from Jeff Gray

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