As Quebec gets wetter because of climate change, risks of landslides increase

Climate change is likely to increase the frequency of weather events that cause landslides in Quebec, like the one that killed two people a week ago, said a researcher who studies natural risks.

Jacques Locat, a professor emeritus at Université Laval, says climate change models predict that southern Quebec will receive between five and 14 per cent more rain by 2050.

That increase in precipitation, his research suggests, coupled with an expected rise in extreme rain events, will make the frequency of landslides in the province more likely.

"The impact of climate change on landslides in Quebec will be mainly related to precipitation," Locat, co-founder of a research laboratory at the university that studies natural risks, said in a recent interview.

On Saturday, torrential rain in Quebec's Saguenay—Lac-St-Jean region contributed to several landslides — including one that led to the death of two people.

That landslide, Locat said, appears to have been caused by erosion along the Éternité River and saturation of the embankment above the river, both of which triggered sandy material on top of the clay soil to slide downward.

Quebec risks having more "superficial landslides," Locat said, which generally involve soil conditions that are particularly susceptible to erosion and to being rapidly saturated with water.

Locat said two factors lead to superficial landslides: erosion of soil at the bottom of slopes — caused by water but also human activity — which makes them more steep, and saturation of the soil at the top of slopes, which causes material to slide downward.

"Erosion is the trigger of many landslides along watercourses and so climate change could have an effect on the frequency and significance of water level increases and, perhaps, an impact on superficial landslides," Locat said.

About 40 per cent of landslides in Quebec's St. Lawrence River valley — a region where they are particularly common in the province — are caused by erosion that is the result of human activities, he said. Landslides also occur around Gatineau, Que., near Ottawa; in the Charlevoix region, northeast of Quebec City; and the Gaspé Peninsula.

All of those regions are located on a clay plain left by a sea that disappeared around 10,000 years ago.

That clay soil can become unstable, and landslides are part of the natural evolution of that type of landscape, he said.

Last summer, more than 70 households were evacuated in La Baie, Que., part of the city of Saguenay, after a landslide destroyed an empty house, and officials feared further slides.

In 1971, a landslide in another part of that city killed 31 people and led to the abandonment of the community of St-Jean-Vianney.

Locat said that what is likely the deadliest landslide in Quebec's history occurred in 1908 in Notre-Dame-de-la-Salette, Que., about 40 kilometres northeast of Ottawa, and killed 33 people.

However, Locat, who studied the event for a 2017 paper, found that the landslide occurred across the river from the town and triggered a sort of "tsunami" that projected ice onto the community and caused the deaths.

Research published by Natural Resources Canada in May 2021 showed that between 1771 to 2019, Quebec had the second highest number of deadly landslides in the country: 239.

Only British Columbia had more, with 356. Quebec was followed by Newfoundland and Labrador, which had experienced 103, and Alberta, where there were 73.

But Locat said Quebec may have a higher number of recorded landslides than other parts of the country because of its settlement patterns.

Around 80 per cent of Quebec's population lives on the clay plain where landslides occur, he said, adding that the province was settled earlier than other parts of Canada, allowing Quebecers a more extended opportunity to record the phenomenon compared with other Canadians.

This report by The Canadian Press was first published July 7, 2023.