How rain and intense storms will change Canada’s alpine environments – and complicate avalanche forecasting

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The atmospheric rivers that caused heavy rains and flooding in British Columbia last year did most of their damage in low-lying areas close to the province’s coast. But they also left their mark on mountain peaks across Western Canada.

One of those peaks belongs to Mount Mackenzie in Revelstoke, B.C., where, buried under dozens of centimetres of snow, there is a thick layer of icy snow called a rain crust, which was created when an atmospheric river drenched the mountain.

James Floyer, the forecasting team supervisor at Avalanche Canada, recently visited the mountain to conduct field work. As he travelled up the slopes on skis, he broke off a piece of the crust and picked it up in his hands. In the right conditions, he said, the smooth, slippery snow could be the perfect platform for a large avalanche to start sliding.

On the south-facing slope of the mountain, where sunlight helps bond different layers of snow, he said, the crust will likely not be problematic. But on the north side, where wind has loaded the mountain with a slab of new snow, there is much more risk of a skier triggering an avalanche. That’s because the new slab hasn’t had time to meld with the icy underlayer, meaning the snow can easily move around.

Avalanche Canada works to provide detailed forecasts of avalanche conditions to skiers, snowshoers, snowmobilers and other people who spend time in mountainous backcountry areas and might find themselves at risk of being caught in a slide. The not-for-profit organization has more than 60 staff throughout B.C., Alberta, the Yukon and Newfoundland.

Mr. Floyer said rain, and rain crusts, are becoming more common in winter alpine environments as climate change affects global weather patterns.

He added that increasingly warm temperatures could lead to much larger avalanches in the springtime, because moisture from melting ice can act as a lubricant between snow layers, potentially setting off very powerful and destructive slides.

Avalanche experts around the region say climate change will complicate avalanche forecasting and prevention, as more intense storms and temperature swings affect snowpacks on Canada’s mountains.

“We keep finding, in the last couple years specifically, there are some anomalies of massive precipitation, wind and snow events that are outside the average,” said John Buffery, a senior avalanche officer with the B.C. Ministry of Transportation and Infrastructure. “We keep having these records broken.”

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Although the risk of avalanches is increasing, the number of fatalities from them in Canada is relatively low. According to Avalanche Canada, there has been an average of 10 deaths a year because of slides over the past 10 years. Death tolls have been in steady decline since the 1990s. The organization said there has been one reported death from an avalanche so far this winter season.

Avalanche Canada attributes the rarity of fatalities to the increasing number of people taking avalanche-safety courses. More than 15,000 people took classes with the organization’s training program this year.

But as climate change forces avalanche forecasters to adapt to new weather patterns, the way they communicate to backcountry users is changing, too.

In early December, Mr. Floyer said, Avalanche Canada advised against all travel in the Western Canada backcountry for only the second time in his memory, after B.C. was hit with its third atmospheric river in a row. (The organization also recommended against all backcountry travel at the beginning of the COVID-19 pandemic, but that was to ensure sporting injuries wouldn’t use up strained health care resources.)

The agency usually tries to guide people toward relatively safe terrain during adverse weather events, rather than advise against any activity at all – but this storm was different.

“The confluence of the extreme weather event, the pressure on the road system, as well as something about COVID and our concern that search-and-rescue capacity in B.C. at that time was diminished, meant we felt that staying out of the backcountry was the appropriate message for that situation,” Mr. Floyer said.

It was an example of how the variables in avalanche forecasting are moving beyond traditional inputs such as snowfall or wind.

Another of those variables is the summer season.

Mr. Buffery said climate-change-related events including mudslides and forest fires have the potential to create new avalanche zones. That’s because trees are a major source of stability for snow. They act as anchors that keep large avalanches from propagating. When they are burned or knocked down, slopes become much more dangerous in the winter.

Mr. Buffery added that weather events such as this past summer’s heat dome, which brought record-high temperatures to Western Canada, will have an effect on avalanches. The heat accelerates the melting of glaciers, some of which are in avalanche zones near highways.

“It’s not even just the direct winter issues, but the whole general scope of the change in climate has really affected avalanches,” Mr. Buffery said. “It’s new for us in the last couple years to have to monitor this.”

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As B.C. adapts to changing weather and environments in the mountains, snow slides are sure to have a financial impact on the provincial government, said Bruce Jamieson, a retired University of Calgary professor who has studied avalanches and now works as a backcountry safety consultant.

Mr. Jamieson said some of the costs will be related to technology used to prevent snow slides from shutting down roads.

“The public tolerance for closures is going down, and that has resulted in governments spending substantially more money on control measures like remote avalanche control systems,” which use explosives to create intentional slides as a way of preventing dangerous snow buildup, he said.

Climate change’s influence on avalanches is less straightforward than its influence on other natural disasters, such as floods and fires, Mr. Jamieson said.

With wildfires, for instance, it’s easy to see a trend: larger fires and longer fire seasons. But with avalanches, there are many things that could be affected by changing weather patterns, including the type of snow falling, whether wind is blowing snow on certain slopes, and how snow bonds to icy rain crusts.

Mr. Floyer said avalanche forecasting is always based on small changes in those factors, which shift with weather systems.

Even if the nature of Canada’s mountain slopes changes over the years, he said, Avalanche Canada will be able to adapt and keep backcountry users informed.

But he acknowledged that climate change could eventually pose a challenge. “Do we need to shift how we build our models? We absolutely have to be aware of it moving forward,” he said.

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