The flooded parking lot of Grand Touring Automobiles, a luxury car dealership on Dundas Street in Toronto’s east end, on July 16.Melissa Tait/The Globe and Mail
The storm that inundated Toronto on Tuesday was actually a series of storms. Following the usual west-to-east pattern of local weather systems, they moved from southwest to northeast and hit the city in quick succession, the first at about 9:45 a.m. and the last about three hours later.
Meteorologists have a name for Events like these: training storms. Like a line of boxcars hooked onto a great freight train, they were hurtling toward the city as if they were on rails. Unlike some storms, they didn’t swerve or dodge. The winds in the low and middle levels of the atmosphere were unusually steady, steering them straight toward Canada’s largest population center. When they arrived, they had a powerful impact.
Geoff Coulson, a veteran meteorologist who answered media calls for Environment Canada the day after the big rain, told me that about a half-dozen storm cells hit Toronto during those three morning hours. By the time the last one passed, 97.8 millimetres of rain had fallen at Pearson International Airport. Considering that Toronto receives an average of 74 millimetres for the entire month of July, that was a huge amount of precipitation.
Additionally, Coulson said, Tuesday’s storms followed two other days of heavy rain, on July 10 and 15, which dumped 46.1 millimetres and 25.1 millimetres respectively. With nearly half the month left after Tuesday, Toronto had recorded more than double its average total for July and was approaching an all-time record for the month.
The amount of rain was staggering. A rain gauge in the city centre recorded 45 millimetres in one hour, or more than half the monthly average in just 60 minutes. Pearson recorded 26 millimetres in 10 minutes.
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The effect was dramatic. The lower stretch of the Don Valley Parkway became part of the Don River, a normally calm stream that overflowed its banks, filling the roadway and leaving cars stranded and drivers in need of rescue. Waves rose up on the flooded Lakeshore Boulevard. Some downtown streets were completely inundated.
Nearly 170,000 residents lost power in their homes. Countless basements were flooded, as was Union Station. Insurers estimated the cost of storm damage at more than $1 billion.
In the aftermath, Toronto was left wondering what it all meant. Was this the new normal? Had Toronto’s leaders done anything to prepare the city for such events, or was the city more or less defenseless?
The concerns were understandable, but it’s worth remembering that while extreme weather events are becoming more common due to climate change, serial storms like Tuesday’s are very rare. Environment Canada says the storm was rarer than a once-in-a-century event. In other words, statistically speaking, the probability of it occurring in any given year is less than 1%.
It is also worth remembering that cities are becoming more capable of defending themselves against natural disasters. When Hurricane Hazel hit Toronto in 1954, dumping 200 millimetres of rain on the city in 24 hours, 81 people died and 1,900 families were left homeless.
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After Hazel, the city moved homes out of river floodplains and placed a series of dams and other controls on local waterways. There were no fatalities Tuesday. Although some subway stations were flooded, most public transportation continued to operate. The Don Valley Parkway reopened the next day. The city’s water supply remained safe and uncontaminated, although beaches were temporarily unusable for swimming due to sewage overflows.
The city is in the midst of a multimillion-dollar, multiyear effort to modernize its sewer and stormwater management systems, including massive diversion and drainage tunnels under the city and into Lake Ontario. The Don River mouth diversion, now nearly complete, will help protect parts of downtown from flooding — though not the Don Valley Parkway, which will require separate upgrades to protect it from flooding.
Much more needs to be done. In the past, Toronto has failed to reckon with the power of nature. It brought that infamous stretch of the Don Valley Parkway almost level with a river prone to flooding. It buried other urban rivers, drained swamps and covered vast swathes of the city with impermeable pavement, letting water spill into streets and underpasses.
Tuesday’s storm was a reminder of what a historic mistake that was and how important it is to correct it.
