Are atmospheric rivers becoming more frequent and severe?

Atmospheric rivers like the historic one that deluged British Columbia five years ago appear to be happening more frequently and with greater severity. That means Canadian P&C insurers and governments could be on the path to higher payouts.

“If atmospheric rivers are, indeed, becoming more common and places like British Columbia see more of these conveyor belts of water bringing copious amounts of rain in short periods, it could very well mean more and higher insured losses for Canadian carriers,” Glenn McGillivray, managing director at the Institute for Catastrophic Loss Reduction (ICLR), tells CU.

“That being said, a lot of people — myself included — believed that insured losses from the November 2021 event were going to be much higher than they were.”

That atmospheric river was B.C.’s costliest severe weather event at more than $675 million in insured damage.

“The scope of that flooding was so wide and damage so intense, it seemed as though it was posed to be one of Canada’s largest insured loss events,” McGillivray says. “But claims were tempered by the fact that many people in that area live in high-risk flood zones and can’t get flood insurance.

“So, while these events may bring more insured losses in general, they will surely mean more and higher payouts for disaster assistance and for governments (i.e., taxpayers) in general.”

Another smaller atmospheric river in December cost about $90 million, Insurance Bureau of Canada reported last month, using figures from Catastrophe Indices and Quantification Inc. (CatIQ).

Climate change impacts

Climate change may be contributing to increased frequency or severity of atmospheric rivers, says Gordon McBean, ICLR’s director of policy studies and professor emeritus at Western University in London, Ont. “With the climate warming, that enhances them. They’re becoming more and more intense and carry more and more water because of the increasing warming.”

McBean describes atmospheric rivers as tracks of air that can hold and transport water in vapour form. And a warming climate increases the amount of water vapour. “If it then goes over land and hits a coastal community, it has this extra amount of water” that can plunge down as precipitation, he says.

Making matters worse, Canada is warming roughly twice as fast as the global average, McBean reports. He adds that when he was head of the Canadian Meteorological Service, the term ‘atmospheric river’ wasn’t often used. “We never used that term much in the Canadian context, but now it’s starting to happen.”

McGillivray points to a study that suggests atmospheric rivers are moving northward, which could mean more impacts to Canada.

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One famous atmospheric river is the ‘Pineapple Express,’ which can cause significant downpours across British Columbia, Washington, Oregon and California. “They can also be on the east coast [of Canada], but they probably don’t get them quite as intensely,” McBean adds.

A study last month in npj Natural Hazards, Atmospheric rivers are associated with nine out of every 10 floods in major global river basins, found that atmospheric rivers are “dominant and widespread drivers of extreme flood events worldwide. Their contributions were evident during and before floods, with influences spanning mid-latitudes to tropical regions, causing human fatalities and population displacements.”

Says McBean: “They have a projected effect on the insurance companies in the amount they’re going to be paying out in losses.”

Jason Contant

Jason has been an award-winning journalist with Canadian Underwriter for more than a decade, including the past three years as associate editor and, before that, as digital editor for seven years.