The flooded parking lot at Grand Touring Automobiles, a luxury car dealership on Dundas Street in the east end of Toronto on July 16.Melissa Tait/The Globe and Mail
The rainstorm that inundated Toronto on Tuesday was really a series of storms. Following the usual west-to-east pattern of local weather systems, they moved southwest to northeast, striking the city in rapid succession, the first at about 9:45 in the morning, the last around three hours later.
Meteorologists have a name for events like these: training storms. Like a line of hitched boxcars in a big freight train, they barrelled toward the city as if on tracks. Unlike some storms, they did not dodge or deviate. The winds in the lower and middle levels of the atmosphere were unusually constant, blowing them straight for Canada’s biggest population centre. When they arrived, they packed an almighty punch.
Geoff Coulson, a veteran meteorologist who was answering media calls for Environment Canada the day after the Big Rain, told me that about half a dozen storm cells hit Toronto during those three morning hours. By the time the final one passed, 97.8 millimetres of rain had fallen at Pearson International Airport. Considering that Toronto gets an average of 74 millimetres in the whole month of July, that was a massive amount of precipitation.
What is more, Mr. Coulson said, Tuesday’s storms followed two other big rain days, July 10 and July 15, that dumped 46.1 millimetres and 25.1 millimetres respectively. With nearly half the month still to go after Tuesday, Toronto had recorded more than double its average total for July and was nearing an all-time record for the month.
The sheer rate of the rainfall was overwhelming. A downtown rain gauge registered 45 millimetres in one hour – in other words, more than half the monthly average in just 60 minutes. Pearson got 26 millimetres in 10 minutes.
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The effect was awesome to behold. The lower stretch of the Don Valley Parkway effectively became part of the Don River, a normally quiet stream that overflowed its banks, filled the highway and left cars stranded and drivers in need of rescue. Waves were kicking up on flooded Lakeshore Boulevard. Some downtown streets were entirely awash.
Close to 170,000 residents lost power to their homes. Countless basements flooded. So did Union Station. Insurers were putting the cost of storm damage at more than $1-billion.
In the aftermath, a shaken Toronto wondered what it all meant. Was this the new normal? Had Toronto leaders done anything at all to prepare the city for such events – or was the city more or less defenceless?
The worries were understandable, but it bears remembering that, even if extreme weather becomes more common because of climate change, serial storms like Tuesday’s are highly unusual. Environment Canada says the storm was rarer than a once-in-a-century event. In other words, statistically speaking, the chance of it happening in any given year is less than 1 per cent.
It also bears remembering that cities are getting better at defending themselves from natural disasters. When Hurricane Hazel struck Toronto in 1954, dumping 200 millimetres 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 housing out of river floodplains and put a series of dams and other controls on local watercourses. No lives were lost Tuesday. Though some subway stations flooded, most transit kept running. The Don Valley Parkway was open again the next day. The city’s water supply remained safe and untainted, though beaches were left temporarily unfit for swimming because of sewage overflows.
City hall is in the midst of a multiyear, multibillion-dollar effort to upgrade its sewer and stormwater management systems, including massive diversion and outflow tunnels under the city and into Lake Ontario. The rerouting of the mouth of the Don River, now almost complete, will help protect parts of the central city from flooding – though not the Don Valley Parkway, which will require separate upgrades to protect it against inundation.
Much more needs to be done. In the past, Toronto has been heedless about the power of nature. It put that infamous stretch of the Don Valley Parkway almost level with a river that is prone to overflowing. It buried other urban rivers, drained marshes and covered vast stretches of the city with impermeable pavement, leaving water to spill onto streets and into underpasses.
Tuesday’s storm was a reminder of what a historic mistake that was and how important it is to make it right.