Recent photo showing Montreal’s tiny islands almost flooded by the Saint-Lawrence (or the Prairies river, its side-arm) because of heavy rainfall. Credit: Ágnes Vári. CC BY.
Protecting nature around urban centres can help safeguard cities from floods according to new research from Canada.
A new University of British Columbia-led study shows that safeguarding key natural ecosystems across Canada can help reduce flood risks for more than half of the country’s urban areas at high risk for flooding.
The research reveals that preserving the most important 5% of watersheds – about 201,000km2 or 2% of Canada’s land – can significantly reduce rainwater runoff, protect homes and livelihoods, and safeguard croplands.
Dr Matthew Mitchell, an assistant professor in the faculty of forestry and the faculty of land and food systems at UBC, said: “This is the first national study to assess the role of Canadian ecosystems in flood prevention and to identify where conservation could have the greatest impact.”
Nature: the flood shield
Upstream watersheds near cities such as Vancouver and Toronto play an important role in protecting 3.7 million people living in floodplains and another 20.1 million nearby – more than half of Canada’s population.
Using global data, Mitchell and his colleagues analysed how land types like forests, wetlands and riparian zones absorb water and reduce runoff.
These natural systems prevent downstream flooding, improve water quality and support wildlife, while reducing reliance on costly infrastructure like dams.
Mitchell said: “Nature-based solutions are highly effective for managing flood risks, and this study shows exactly where conservation can make the biggest impact.”
Conservation priorities across Canada
The study identified key ecosystems in British Columbia (BC) that are critical for flood prevention:
- Alpine and subalpine ecosystems in the Coast and Columbia Mountains, which help regulate water flow and prevent downstream flooding;
- Wetlands in the Fraser River Delta, including Burns Bog and other peatlands, which are crucial for flood protection in the Lower Mainland; and
- Forests and wetlands in the Okanagan and Similkameen valleys, which protect key agricultural areas and growing population centres.
Beyond BC, the researchers recommend the following conservation priorities:
- Prairie Provinces (Alberta, Saskatchewan, Manitoba): Protect grasslands and wetlands in key river watersheds, such as the Red and Saskatchewan Rivers;
- Northern Regions: Prioritise conservation in northern wetlands and other ecosystems, including those in the Yukon and Northwest Territories; and
- Southern Ontario: Safeguard wetlands around the Great Lakes and major rivers to reduce flood risks in cities like Toronto, Ottawa, and Hamilton.
Canada has committed to protect 30% of its lands by 2030, yet only 8% of the most flood-critical ecosystems are currently protected.
The researchers call for stronger conservation policies and funding to prioritise these high-impact areas.
Mitchell said: “This research makes it clear that conserving nature isn’t just about biodiversity – it’s also about protecting communities and making cities more resilient to climate change.”
The study is published in Ecosystem Services.
