Prime minister Trudeau and others walking over a flood damages, sandbagged area that is covered with debris.
Weather

Environment Canada links B.C. floods to human-induced climate change

By Natasha Bulowski, Canada’s National Observer, Local Journalism Initiative Reporter

Human-induced climate change “contributed substantially” to the atmospheric river and ensuing floods that devastated B.C. last year, a new study by Environment Canada scientists confirms, warning Canadians to brace for more of the same.

“The chance this kind of flood will happen has increased by 100 to 300 per cent due to human influence,” Xuebin Zhang, a senior research scientist with Environment and Climate Change Canada, told Canada’s National Observer.

The two-day atmospheric river that swept across southern B.C. in mid-November led to the deaths of at least five people, caused multiple evacuations and is the costliest natural disaster in B.C.’s history, with a hefty price tag of $7.5 billion for infrastructure damage alone.

Atmospheric rivers are large, narrow ribbons of water vapour that travel through the sky, typically picking up vapour in the moist air of tropical regions and dropping it in cooler regions.

“Events like what happened in British Columbia will happen more often, and perhaps with even bigger magnitude,” said Zhang. “Engineers and also citizens will need to think about how they are going to deal with this.”

The study is a preprint, which means it has not yet been peer-reviewed, but Zhang says he doesn’t expect many modifications will have to be made before publication.

Although snowmelt contributed to the flooding, Zhang said the main cause was the two days of “intense precipitation” from the atmospheric river.

The intensity was roughly a one-in-10-year event, but the precipitation over those two days was more unprecedented, an approximately one-in-50- to 100-year event, the study noted.

It also found the probability of an equally strong or stronger atmospheric river has increased by at least 60 per cent thanks to the effects of human-induced climate change, which has also increased the chance of such significant two-day rainfall by an estimated 50 per cent.

Last summer, Natural Resources Canada published a 734-page report to inform the national adaptation strategy the government promised in its December 2020 climate plan. The report identified “large gaps” in Canada’s climate change preparedness and highlighted the benefits of investing in adaptation to limit costs of climate change-related weather events.

To prepare for the increased magnitude and frequency of extreme weather events, Canada needs to complete its national adaptation strategy, extend national flooding risk mitigation and appoint a natural disaster resilience adviser, a coalition called Climate Proof Canada says.

Unlike other studies that can take upwards of a year to complete, this one was completed in a few months, Zhang said.

Time was of the essence because the public increasingly wants more information on events like this and whether they can be linked to climate change, said Zhang.

He said senior management at Environment Canada prioritized the study to try to answer the questions so many Canadians are asking. The information will also prove valuable in terms of climate change policy across the country, according to Zhang.

Top photo credit: Canadian Prime Minister Justin Trudeau visits Abbottsford with Mayor of Abbotsford Henry Braun, after rainstorms lashed the western Canadian province of British Columbia – photo by Hailey Sani via Flickr (Public Domain)

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