Severe impacts of flooding created by perfect circumstance storm in southern British Columbia

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The atmospheric river that flowed through British Columbia last week, which caused severe flooding that destroyed homes and highways, was just one of the factors that caused such extensive damage across the province.

A perfect storm of circumstances led to the devastation, and climate scientists say it’s a combination we’ll likely see more frequently and severely in the future.

“The return period from this past event was over 100 years for many of these locations,” said Armel Castellan, meteorologist in charge of warning preparedness for Environment and Climate Change Canada.

“It’s more than generational. It’s like a lifetime event and more, and I think it puts into perspective what we’re going to face in the years and decades to come.”

A study by Environment and Climate Change Canada published in 2020 found that climate change has made precipitation more extreme and storms with extreme precipitation more frequent.

Castellan says that on average, British Columbia can have up to 30 atmospheric rivers per year, although the smaller ones are actually beneficial to the ecosystem.

But when they are more intense, releasing more water and over longer periods of time, these systems become dangerous.

An aerial view of where the Trans-Canada Highway crossed the Sumas Plains in Abbotsford, British Columbia, covered in water, taken Tuesday. (Gian Paolo Mendoza / CBC)

Add in the Drought BC, saw over the summer, forest fire activity the ground shift this year and other recent years, and a thin blanket of snow melting over the mountains, and you have the right scenario for major floods and landslides.

Other extreme weather conditions have hit the province this year, including a heat dome that killed hundreds people and led to an intense forest fire season, and a tornado that swirled near the University of British Columbia earlier this month.

“There were things that conspired against this event to create such a bad set of impacts that continue today,” Castellan said.

On average, Vancouver receives about 185 millimeters of rain in November. Many parts of the region exceeded that amount in less than 48 hours last week, and more rain is expected.

Annual floods of “historic” proportions by the end of the century

Two years ago, climate change researcher Charles Curry co-authored an article suggesting that extreme precipitation events would result in maximum annual flooding of historic proportions by the end of 2100 in the Fraser River Basin.

“What the models are telling us is kind of a glimpse or kind of likelihood that these events will become more frequent in the future,” Curry said.

“But we just can’t say the same about exactly when they’re going to happen.”

That said, he was surprised by the intensity of the precipitation this month.

Community volunteers fill and deliver sandbags to farms in the Sumas Prairie flood zone in Yarrow, B.C. on Friday. (Ben Nelms / CBC)

Curry says atmospheric riverine events of varying intensity each year tend to hit different regions of the province – the northern tip of Vancouver Island, for example, which tends to receive a lot of rain.

“It is less common to see an atmospheric river entering just beyond the southern tip of Vancouver Island … then into the Fraser Valley, sinking as deep as the Fraser Valley, and we have seen that -Here, ”said Curry.

“It is particularly dangerous because the quantity of water carried by these atmospheric rivers is very large and they do not really release this water before reaching a certain topography, mountains where they must rise and where the air. gets colder and all that moisture that can just fall out of the atmosphere as rain. “

Atmospheric rivers (or ARs) are large, narrow streams of water vapor that cross the sky. (SRC)

Site warning system

Castellan said his organization was working with meteorologists around the world to develop a scale for atmospheric rivers, much like those used to describe the severity of hurricanes.

Hurricanes are called, for example, a Category 1 hurricane, which would indicate sustained winds of 119 to 153 km / h.

At the other end of the scale, a Category 5 hurricane indicates long-lasting winds above 249 km / h.

Such a scale could help local governments and residents plan and prepare for events like the one that just happened in British Columbia two to three days before he arrived, Castellan said.

“For current generations we are going to have to adapt to the most extreme weather conditions in the future, and atmospheric rivers are certainly one of them,” he said.

Curry also said that atmospheric rivers also have a distinct advantage: they can be predicted.

“This particular event was also scheduled. We got 48-72 hours’ notice from the meteorologists. It was a pretty good idea of ​​where this atmospheric river would strike, although we didn’t necessarily know the rainfall intensity, ”he said.

“So once you get that kind of information you can start making plans.”

Cows stranded in a flooded barn are rescued in Abbotsford, British Columbia on Tuesday. (Jennifer Gauthier / Reuters)

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