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Water surrounds homes and farms in the Sumas area on Nov. 18, 2021 in Abbotsford, B.C.Rich Lam/Getty Images

Journalist Peter Kuitenbrouwer is a Registered Professional Forester.

Startling photos have been circulating this week of the floods in B.C. In one, the city of Merritt, near Kelowna, lies submerged. Some conifers and other trees speckle the watery lawns; evergreens dot a hillside. As in much of B.C., and, indeed, across southern Canada, Merritt settlers cleared dense forests to make way for the houses, roads and parking lots of our communities. In Abbotsford, another city suffering from the floods, a recent photo shows a local farmer using a Sea-Doo to tow a terrified Holstein. Abbotsford is now a farm centre, but began life as a mill town.

Many people are bemoaning the failure of world leaders to make meaningful progress to curb climate change at the COP26 summit in Glasgow. But we needn’t twist arms in Scotland to combat global warming, when solutions lie here at home. Did climate change cause the storm that engulfed much of B.C.? Certainly it contributed. Another factor is logging, which has left the landscape denuded of the forests that absorb rainwater and mitigate the effects of torrential rainstorms.

I was born in B.C. and have three siblings there, plus an uncle, two aunts and plenty of cousins. My heart goes out to everyone struggling with this emergency. At the same time it’s important to underline the role that trees play to mitigate floods.

Among their marvels, trees perform something called transpiration: they suck water from the ground, which transpires through their needles, or leaves, into the air. The U.S. Geological Survey notes that a large oak can transpire 150,000 litres of water a year; this water stays out of rivers and sewer pipes.

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Peter Wood, a PhD in forestry from the University of Toronto, in February wrote a report titled Intact Forest, Safe Communities, released by Sierra Club BC. Dr. Wood described how intact forests mitigate floods: they “serve as giant sponges, absorbing, storing, and then releasing water slowly, providing for year-round moisture, cool micro-climates, and water purification.”

Last year, Insurance Business Canada magazine quoted Younes Alila, a forest management professor at the University of British Columbia, saying logging at higher elevations in mountainous areas can increase the frequency of flooding events downstream. “We’re going to continue to see an increase in the flood risk for decades to come,” Dr. Alila said. The effect is long-lasting since trees grow slowly.

In a working forest, one cuts trees while letting others grow, in a constant cycle. These forests function as sponges. In Abbotsford, locals deforested instead. Abbotsford’s mill in the 1920s was one of B.C.’s busiest, producing 20 million board feet of lumber and as many shingles each year. By 1934, according to the Forest History Association of British Columbia, “all the surrounding area had been logged,” and the mill shut down.

Not long ago a friend loaned me John Vaillant’s book The Golden Spruce, about a B.C. timber scout who in 1997 cut down an emblematic Sitka spruce in Haida Gwaii, which by some mutation grew golden rather than green needles. Grant Hadwin felled the celebrated, 300-year-old giant as a quixotic protest against the wholesale removal of B.C.’s cedar, Douglas fir, hemlock and spruce. Mr. Vaillant describes the brutal efficiency with which lumber interests cut B.C.: “A two-hundred-ton tree that has stood, unseen, for a thousand years and withstood wind, fire, floods and earthquakes can be brought to earth, rendered into logs, and bound for a sawmill in under an hour – by just three men.”

B.C. may wish to protect more of its intact forests, to soak up water. That said, these days governments require timber companies to ensure forests grow back, often by planting trees. Can we replace what we have cut? We can try. Prime Minister Justin Trudeau’s pledge to plant two billion trees by 2030 (on top of those the forest sector plants) is a good start, and coincides with the United Nations Decade on Ecosystem Restoration.

Tree planting can mitigate floods. Settlers cleared southwestern Ontario for agriculture; in 1937, the Thames River flood submerged parts of London, Ont. The flood propelled the creation of conservation authorities to reforest southern Ontario. In 1941, Edmund Zavitz, the father of tree-planting in Ontario, told a London conference virtually the same message Sierra Club BC echoed 80 years later. “The fact that forest cover prevents rapid run-off of rains and melting snow,” Mr. Zavitz said, “makes it important that a good percentage of the watershed of our rivers be kept under forest cover.”

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