Severe weather: should we brace for more?
If not microbursts, we can expect more flooding, expert says
Relentless spring rain floods hundreds of Montreal homes. A microburst rips through Notre-Dame-de-Grâce, leaving a trail of damaged trees, cars and houses.
For one, there is no evidence of a link to climate change. For the other, there is.
The weather event that hit N.D.G. Tuesday was a microburst.
Associated with severe thunderstorms, a microburst is “a very intense downdraft of air that brings with it strong, fast winds that push outward when they reach the ground,” Environment Canada says.
In N.D.G., winds reached 120 kilometres per hour.
Two key ingredients are required to create a thunderstorm: moisture and an unstable atmosphere, said Eyad Atallah, a research associate and course lecturer at McGill University’s Department of Atmospheric & Oceanic Sciences.
“While climate change is contributing to the amount of moisture in the atmosphere, it’s unclear that it’s actually contributing to how unstable the atmosphere is,” he said.
“There’s nothing observationally to suggest as of yet that we’ve seen any significant changes in the behaviour of severe thunderstorms.”
It’s a different story when you consider the large-scale flooding that parts of Montreal experienced in April and May.
It was caused by a slow-moving low-pressure system that dumped heavy rain in the region, followed by abnormally warm weather that contributed to the flooding by melting snow, Atallah said.
“Both of those things are more likely to occur more often in the context of global warming.”
Should Montrealers be bracing for more such flooding?
“If you look at most of the literature, the expectation is that flooding in general will increase around the world, and I don’t see any reason to think this kind of thing would not become more frequent” in Montreal, Atallah said.
There have been nine microbursts in the Montreal area during the past decade.
An average of six microbursts occur in Quebec every year, said Environment Canada meteorologist Amélie Bertrand. So far, there have been six in 2017.
“There’s nothing really abnormal in this,” she said.
“These kinds of phenomena happen almost every summer in some part of Quebec.”
On Tuesday, the microburst happened to hit a densely populated area with many mature trees.
“If it had been in a suburb without many trees, there probably would have been less damage,” Bertrand said.
The violent storms that rolled through Quebec on Tuesday also resulted in a tornado in Lachute, 80 kilometres northwest of Montreal.
About six tornadoes touch down in Quebec every year. The one in Lachute was the sixth of 2017.
“Every summer is different,” Bertrand said.
“Sometimes, they’re more active;
There’s nothing really abnormal in this. These kinds of phenomena happen almost every summer in some part of Quebec.
others are less active. Thirty years ago, Montreal was flooded by a few thunderstorms; people were stuck in their cars on the Décarie Expressway.”
She noted that in 1994, 15 tornadoes whipped through Quebec. In 2015, there was only one.
“There has been severe weather in the past just as we see it today,” Bertrand said.