Floods in British Columbia | Clear cuts pointed out

The forestry industry contributed to recent catastrophic flooding in the interior of British Columbia, various observers say. Quebec, which has comparable practices, is unlikely to suffer the same fate, experts say.

When the green gets swallowed up

The deforestation around Merritt and Princeton is striking from the air.

The two towns in the interior of British Columbia, heavily affected by flooding for nearly two weeks, were surrounded by dark green forests in 1984.

Mais au fil du temps, « on voit le vert se faire engloutir » par les coupes à blanc, montrent des images prises par satellite relayées par le documentariste Daniel J. Pierce, qui se penche depuis une dizaine d’années sur l’industrie forestière britanno-colombienne.

« Je ne suis pas un scientifique, mais d’aucune façon couper autant de forêt ne peut se faire sans impact sur l’hydrologie d’un endroit », affirme-t-il dans une vidéo publiée dans les premiers jours des inondations qui a accumulé plus de 50 000 visionnements.

L’auteur du film Water Logged (combinaison de l’expression « gorgé d’eau » et d’une allusion à l’exploitation forestière), qui dénonce le lien entre les coupes à blanc et les inondations ayant frappé Grand Forks, en 2018, n’écarte pas l’influence sur les inondations actuelles d’autres facteurs comme les précipitations anormales et les incendies de forêt, mais il affirme que les pratiques forestières y sont aussi pour quelque chose.

Scientists agree … in part

Scientists consulted by Press are also of the opinion that deforestation may have played a role in the flooding that hit the interior of British Columbia – which excludes those in Abbotsford, in the southwest of the province – but point out that this this is not just attributable to logging.

“If there is something that could explain the floods, it would be fires more than clear cuts, because there have been quite a few more around Merritt,” says Professor Gregory Paradis, of the department of University of British Columbia Forest Management, discussing the major fires of last summer and those of 2017.

“But clearcuts also contribute,” he adds, explaining that scientific studies have shown that logging has certain impacts on hydrological processes in forests.

“Among other things, clear cutting tends to increase the level of the water table,” he illustrates.

The hydrology of a watershed is “highly sensitive” to logging, in south-facing “mid-elevation” sectors, two of his colleagues from the University of British Columbia concluded. in 2019.

Their study, whose “findings challenge prevailing knowledge,” found that removing only 11% of trees in a watershed doubles the frequency of floods and increases their magnitude from 9 to 14%.

Merritt and Princeton are precisely in an area of ​​accentuated topography, remarks Gregory Paradis.

The forest, a sponge

Trees are an obstacle to rain; they slow down its fall to the ground and even absorb part of it.

Shade from trees also slows down the process of decomposing organic matter on the soil, which also slows down rain, while their roots hold the soil in place.

“When we cut [les arbres], decomposition is accelerated to expose the mineral soil [et quand] the water falls, it will fall more directly on the ground than when we had forests, ”explains Professor Paradis.

“The forest acts like a sponge, a big sponge,” says Jens Wieting, science advisor for forests and climate at the Sierra Club of British Columbia, a non-profit environmental organization.

The water runoff was also facilitated by the forest fires of last summer, which “cooked the soil” and made them hydrophobic, adds the specialist in forest hydrology Sylvain Jutras, professor at the Laval University, in Quebec.

Review forestry practices

Flooding in the interior of British Columbia is “a terrible example of the combination of forest degradation and extreme weather events exacerbated by the climate crisis,” says Jens Wieting

His organization had also published earlier this year a report sounding the alarm on the “catastrophic impacts” that industrial forestry in British Columbia could have on 15 climate risks, including floods and landslides, but also water shortages and forest fires.

British Columbia’s forestry practices are not based on the latest scientific knowledge, laments the province’s Sierra Club.

Documentary filmmaker Daniel J. Pierce agrees, believing that Victoria should reorient its forest industry by prioritizing water management, a need that will become increasingly urgent with the climate crisis.

“We could work to regenerate our watersheds, our forests could be our best allies; climate change is here, it will not go away, ”he said in an interview with Press, worrying that cuts are increasing in mountainous areas at risk.

Professor Gregory Paradis is also critical of British Columbia’s forest management: “Roughly speaking, all we do is clear cuts and replant afterwards. ”

He laments that the models that determine the volume of wood that can be harvested “do not easily include natural disturbances such as fires, windfall, insects and climate change”.

The British Columbia government recognizes that “logging can contribute to flooding”, but claims to focus on “a scientific approach to reforestation to [en] reduce the risk, ”said in an email to Press a spokesperson for the Ministry of Forests, Lands, Natural Resources Exploitation and Rural Development, Nigel McInnis.

Improbable in Quebec

It is unlikely that the clearcuts will contribute in Quebec to floods like the one currently hitting the interior of British Columbia, believe various experts.

The risk is “very, very low,” says Professor Sylvain Jutras, from Laval University, a specialist in forest hydrology and a forest engineer.

He cites as proof the scientific literature “extremely clear” as to the fact that in northeastern North America, the effects of logging on the hydrology of watersheds are very low below 50% harvest or disturbance, unlike the mountainous areas of western Canada.

Mr. Jutras estimates that “in the worst situations, we reach 10 to 35% in equivalent cutting area”.

Researchers from Laval University have carried out research in the Montmorency forest, north of Quebec, in recent years, and have not detected any change in the rainfall regime after a forest cut in 50% of the area, explains Sylvain Jutras.

Other factors

Other factors also reduce the risk that deforestation contributes to flooding in Quebec, estimates Professor Sylvain Jutras.

Clearcuts, which are the dominant type of harvest in the boreal forest, are not in the mixed forest of southern Quebec, he explains.

The urban agglomerations on the north shore of the St.Lawrence are well fed by watersheds that go back to the boreal forest, where there are clearcuts, but forest fires are rare there, he continues. , warning however that this could change with climate change.

It is rather western Quebec that is suffering from forest fires at the present time, but this is the James Bay watershed, sparsely inhabited, adds the professor.

Not all deforestation is attributable to the forestry industry, particularly in southern Quebec, where agricultural and commercial needs are often the source of deforestation, specifies Sylvain Jutras.

Quebec’s forests are also less accentuated than those of British Columbia, observes Professor Gregory Paradis, also of the opinion that flooding attributable to logging is unlikely in Quebec.

Alarm signal

One big unknown, however, should prompt caution, believes Jens Wieting, science advisor for forests and climate at the Sierra Club of British Columbia: the climate crisis.

Flooding in western Canada should be “a wake-up call to all parts of Canada,” says the ecologist, who believes provincial governments should review and change their forestry frameworks in light of what is happening in British Columbia.