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Just as record-level flood waters that triggered widespread evacuations begin to recede in western Washington state, residents of the Pacific north-west are bracing themselves for another strong weather system that is likely to swell rivers back to dangerous levels – again.
An extraordinarily strong system known as an atmospheric river hit the region earlier this week, dropping more than a foot of rain and flooding rivers that stretch across the state toward Canada to dangerous levels. As a result of the nonstop rain, mudslides tore through communities, washing away homes and stranding families on rooftops as they waited for rescue.
The bouts of heavy rain have caused flooding beyond Washington, spreading into British Columbia, where landslides and flooding forced even more people to evacuate and shut down several major highways leading to Vancouver.
While atmospheric rivers are not uncommon in the Pacific north-west this time of year, these back-to-back systems are unusually potent and are causing cross-border problems in the US and Canada.
What are atmospheric rivers and why are they getting worse?
As water flows through rivers on land, atmospheric rivers are large channels in the atmosphere that transport water vapor from the tropics and are essential to the world’s annual water supplies. In the Pacific north-west, atmospheric rivers typically occur during the fall and winter, bringing water-laden air from areas around Hawaii to the west coast.
Meteorologists say the severity of this specific weather event is due in part to moisture from even farther in the western Pacific near the Philippines.
At their most beneficial, these systems can bring much-needed rain to drought-prone areas, according to the US Department of Agriculture. In extreme cases, such as the recent deluge over Washington and Oregon, heavy rains from these atmospheric rivers can bring devastating floods and mudslides.
While most of the American public has focused on the swelling rivers and damage that floods left behind in western Washington, neighbors to the north in Canada’s British Columbia face their own problems.
And some experts believe the US should take action to prevent potential flooding across the border.
Can Canada rely on the US to make infrastructure upgrades to stop cross-border flooding?
As Washington’s Nooksack River flooded this week, sending a surge of water north over the border into British Columbia, some Canadians were haunted by memories of flooding that devastated the neighboring community in 2021.
Four years ago, when the Nooksack River overflowed, pushing a large amount of water north into the Sumas prairie in Abbotsford, BC, it triggered a record-breaking flood event that forced people to evacuate, shut down major highways and caused over a billion dollars in damages, as the Canadian Press reports.
While the Nooksack River does not cross the Canadian border, when flooded, the river’s water does overflow into areas near the border, posing a major flood risk to Canada. According to a Globe and Mail report in 2021, Canadian politicians and engineers had urged government officials in Washington state to invest in flood-prevention infrastructure at the Nooksack River to address potential threats.
Canadian flood risk researcher Charlotte Milne told the CBC in a report published on Friday that the US has been slow to take action to address cross-border flooding.
While Milne acknowledged that some US initiatives have begun to address the watershed issue, including the Snohomish Watershed Resilience Action Plan and the Nooksack and Sumas Transboundary Flood Initiative, she argued they should have started sooner.
“It’s not that people aren’t thinking about these things. They do take a while. But I do think they could have come a little quicker,” Milne told the CBC.
The Nooksack and Sumas rivers reached record levels again during the storms this week. As of Friday evening, 500 properties were under an evacuation order in Abbotsford and only one flood warning remained in place for an area near a BC section of the Sumas River.
Researchers have found that the human-caused climate crisis has contributed to the severity of weather events, including atmospheric rivers. According to studies conducted by the US Geological Survey, researchers have observed a pattern of increasing water vapor transport to the west coast over the past 70 years, which they have associated with the warming of the ocean surface.
Washington-based meteorologists estimated that this week’s weather system brought in over 5tn gallons of rain to the state over seven days, the Associated Press reported.
Speaking to the press this week, Washington’s governor, Bob Ferguson, highlighted the severity of the latest weather systems.
“The flooding levels we’re looking at are potentially historic in nature,” Ferguson said during a Thursday press conference. “I just want to emphasize how serious the situation is.”
