How attribution science can explain the rising number and intensity of floods in BC
Devastating floods have become an increasingly common part of life in British Columbia. In the late 1990s, BC’s Cariboo region experienced numerous floods and landslides. The ‘flood of the century’ happened in fall 2003 when hundreds of Squamish and Paradise Valley residents were forced to evacuate their homes. Later, a 2018 flood event in Grand Forks caused extensive damage, impacting more than 400 homes, farms and businesses. In 2021, successive atmospheric rivers in BC’s Pacific north-west caused billions of dollars in damage from catastrophic flooding and triggered landslides that killed five people.
Urban encroachment on floodplains and climate change are partly to blame. However, they cannot fully account for a trend that has many researchers, including UBC Forestry & Environmental Stewardship Prof. Younes Alila, ringing alarm bells. Through scientific inquiry and the application of a framework known as attribution science, Younes’s investigations have revealed important data on the root causes of more frequent and severe flooding in the province.
The science of attribution
Attribution science has traditionally been applied to climate change research to analyze whether or not extreme weather events can be traced back to a single cause.
Climate change attribution has made significant advances in recent years, but has rarely been applied to extreme events, such as major floods. These events often involve complex interactions that make it hard to identify a single cause.
Using historical data, Younes and his team have been able to link more frequent and severe flooding to areas with substantial forest cover loss at their headwaters — highlands from which tributaries flow.
“People living in these areas consistently find themselves on flood watch, indicating that certain regions of the province are regularly at risk of flooding,” says Younes. “It appears as if these compromised watersheds have exceeded their resilience threshold, making them unable to withstand flooding events any longer.”
Land use changes often associated with urbanization, agricultural practices, mining and various other activities also contribute to soil instability and displacement that can increase the risk of severe flooding. Similarly, landscape hydrology can be altered by changes to forest cover from clearcut logging, beetle infestations or wildfires, as can flood management policies that heavily rely on downstream infrastructure to hold back rising water levels, such as dykes, bridges and culverts, Younes concludes.
“It is important to consider the causes behind why some areas have become community flooding hotspots,” states Younes. “While government agencies and the public often attribute these events to global warming, other equally significant, or potentially more impactful, factors are exacerbating the risk of these extremes.”
Attribution Science Defined
According to Certified Consulting Meteorologist, Jim Foerster, the emerging study of attribution science involves the analysis of causal links between climate change and extreme weather events, such as heat domes, forest fires, floods and atmospheric rivers. To date, several published research papers have drawn connections between extreme weather events and the effects of human-caused climate change from the emission of greenhouse gasses from such things as the burning of fossil fuels, states Jim in a 2023 Forbes article. For example, research found that climate change-related stressors significantly increased the amount of rainfall during the Category 4 Hurricane Harvey that hit southeast Texas and southwest Louisiana in 2017.
A flood of legal action
When it comes to flooding and the application of attribution science, the public, including legal authorities and insurance companies, is taking notice.
In 2015, Younes served as an expert witness in a case involving a BC rancher who successfully secured a settlement against a forestry company that had clear-cut logged near the rancher’s home. The prosecution argued that the logging had significantly and detrimentally altered the water flow in a nearby creek, leading to flooding that decimated 35 hectares of the rancher’s lands. For a 2022 provincial court case, Younes drafted a 70-page report that outlined how clear-cut logging and other activities had likely contributed to two instances of flooding within six years at a couple’s acreage south of Smithers, BC. The $300,000 settlement that the couple received from the province made headline news across the country and in other parts of the world.
Younes is currently working on providing expert testimony for another ongoing court case in BC where clear-cut logging is in question.
Solutions require new ways of thinking
With much of the province’s landscape affected by climate and land-use changes — including forest cover loss — mitigation and management solutions are urgently needed.
“It all starts with a fundamental shift in mindset,” says Younes. “Logging practices within the province’s Timber Supply Areas need to be updated in favour of abandoning clear-cut logging for biodiverse-friendly, restorative practices, including selective, strip-cut and small-patch logging.”
“We must synchronize our flood management strategy in the more populated lowlands with our land use, forest resources and water resources management policies in the uplands.”
A concerted effort among different levels of government, as well as non-governmental leaders and industry, is needed now to make a meaningful contribution to addressing some of the root causes of flood risk, adds Younes.
in the Spring 2024 issue of Branchlines Magazine. View the full issue here.
