Floods in British Columbia | New perfect storm in sight?

Southern British Columbia is crossing its fingers as heavy precipitation threatens to exacerbate an already chaotic situation. Three atmospheric rivers are expected over the next few days, one of which could carry up to 100mm of rain into the still-flooded Fraser Valley. A disaster that looks like a perfect storm, the consequences of which are aggravated by human activities.

Eric-Pierre Champagne
Press

What is an atmospheric river?

The phenomenon is not new, but its name is rather recent. Researchers at the Massachusetts Institute of Technology named this manifestation of the weather in 1998. The recent torrential rains that fell in British Columbia were the result of one of these atmospheric rivers. Three more are planned in the coming days, says Armel Castellan, meteorologist at Environment Canada. The first could bring 40 to 80 mm of rain between Wednesday evening and Friday. Precipitation could also exceed 100 mm in some areas. A second is due on Saturday and a third “which has the potential to be worse than the first” will arrive on Monday, added Mr. Castellan. “There won’t be much respite between each one when the rivers are already saturated. Add to this that the relief increases the risk of flooding in this region of the country. “The very steep slopes of the terrain force the precipitation to fall in a very narrow area,” recalls Richard Harvey, retired meteorologist and climatologist from Environment Canada. With climate change, the duration and intensity of atmospheric rivers are also expected to increase by 50%.

The forest industry in the dock

In a report released less than a year ago, in February 2021, the environmental group Sierra Club stated “that industrial logging has a significant impact on the severity and frequency of climate risks for communities in Colombia. British ”. The study reported that the majority of the 15 climate risks identified by the province are influenced by logging, particularly clearcutting. These included in particular floods and landslides.

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Forest fires promote flooding

The summer of 2021 was particularly devastating in British Columbia with forest fires that ravaged the village of Lytton, 200 km north of Abbotsford. The area burned in the region totaled 25.4 km^⁠2. These fires increase the risk of flooding during heavy rains. Normally, trees and their roots represent natural obstacles to the flow of water. After a forest fire, the soil becomes “hydrophobic”, ie it no longer absorbs water. Under these conditions, the risk of landslides is also higher after heavy rains.

Heat dome and drought make it worse

The dome of heat that plagued British Columbia last summer also paved the way for the flooding of the past few days. “The crux of the matter is the water cycle,” explains Richard Harvey. In a warmer atmosphere, the water cycle will be accentuated. When it rains, it will rain even more. When it is dry, it will be even drier. Scientists also explained that this heat dome would have been almost impossible without climate change. At the same time, the intense drought also deprived the soils of their capacity to absorb so much water in a short period of time.

An old lake that wants to take its place

To all these “prerequisites” put together for a perfect storm, we must add the fact that part of the Fraser Valley was once … a lake. Sumas Lake was drained in the early XX^e century to become the prairie of the Sumas. The authorities then created one of the most fertile agricultural areas in the country, which nevertheless remains a sector at risk. Despite human intervention, the conditions favorable to the presence of a body of water are still real. Authorities are now crossing their fingers that repairs to the seawall protecting Abbotsford and the pumping station hold up. “If we get 100mm of rain in 24 hours, we’ll have a big problem,” admitted city mayor Henry Braun.

With the collaboration of Coralie Laplante, Press