SCIENCE OF FORESTS AND FLOODS IN BRITISH COLUMBIA: “A forest’s influence on flooding stems from the many random or ‘chancy’ features in a watershed,” stated UBC forestry professor Younes Alila in calling for a rethink of forestry practices and policy
Note to Reader:
It is time to rethink forestry practices and policy, according to researchers at the University of British Columbia. They looked at past hydrology studies and found that many severely and consistently underestimated the impact of forest cover on flood risk, therefore leading to poorly informed forest management policies and practices. This call is emphasized in a peer-reviewed article published recently in the journal Science of the Total Environment.
In B.C.’s forests, a debate over watershed science with lives and billions at stake
For more than a century, Dr. Younes Alila explained in a news release from the University of British Columbia, scientists have clung to a “deterministic” analysis. To use a strategic board game analogy, this is like looking at each move in isolation and thinking, “If I move here, then I should win.” It fails to account for the roll of the dice, the cards you draw, and what your opponents might do—all of which can change the game.
When it comes to understanding how logging might increase flood risk, a deterministic approach would look at the logging alone and try to figure out its direct effect. But the risk of flooding is influenced by many things, such as how much snow is on the ground, whether it’s melting or not, how much rain is falling, and the characteristics of the landscape itself. These factors interact over time in complex ways.
Taking them all into account is called a “probabilistic” approach and provides a better overall picture of flood risk. It’s like a savvy board game player considering all the game’s variables instead of just one.
“The probabilistic approach is already well established in other disciplines such as climate change science. It is the most accurate method for evaluating the effects of deforestation on floods,” said Henry Pham, a student in UBC’s master of science in forestry program.
B.C.’s Fraser Valley in November 2021. Credit: UBC Applied Science
Forests can lower flood risk
Dr. Alila says the probabilistic framework is designed to understand and predict, for instance, how much of the 2021 Fraser Valley floods could be attributed to climate change, land use change or logging. The approach also can be extended to investigate the causes of flood risk in other cities and regions.
He added: “In B.C. alone, the flood risk is escalating as we continue to lose forest cover due to ongoing large-scale logging and wildfires. If we want to mitigate the costs of disasters like the 2021 flooding in the Fraser Valley or the 2018 flooding in Grand Forks, we need to change the way we manage our forest cover. Regenerative practices such as selective logging, small patch cutting, and other alternatives to clear-cutting are an important way forward.”
Pham noted that clear-cut logging causes more severe and much more frequent floods, and such floods can have harsh consequences.
Dr. Alila concludes, “Forests serve as the most effective natural defense against a global escalating flood risk attributed to factors such as climate change. Now is the time for water and forest management policies to start being guided by the most up-to-date and defensible science.”
To Learn More:
To read the paper published in the journal Science of the Total Environment, download a copy of Science of forests and floods: The quantum leap forward needed, literally and metaphorically.
To read an article published by the Vancouver Sun newspaper in March 2024, click here or download a PDF copy of In B.C.’s forests, a debate over watershed science with lives and billions at stake.
