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Protecting nature can safeguard cities from floods

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 work is in the journal Ecosystem Services. It offers a global roadmap for integrating nature-based solutions into urban planning and flood management.

The research reveals that preserving the most important 5% of watersheds—about 201,000 square kilometers, or 2% of Canada's land—can significantly reduce rainwater runoff, protect homes and livelihoods, and safeguard croplands.

"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," said Dr. Matthew Mitchell, an assistant professor in the faculty of forestry and the faculty of land and food systems.

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, Dr. Mitchell and his colleagues analyzed 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.

"Nature-based solutions are highly effective for managing flood risks, and this study shows exactly where conservation can make the biggest impact," said Dr. Mitchell.

Conservation priorities across Canada

The study identified key ecosystems in British Columbia 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.
• Forests and wetlands in the Okanagan and Similkameen valleys, which protect key agricultural areas and growing population centers.

Beyond British Columbia, 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: Prioritize conservation in northern wetlands and other ecosystems, including those in the Yukon and Northwest Territories.
• 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 protecting 30% of its land by 2030, yet only 8% of the most flood-critical ecosystems are currently protected. The researchers call for stronger conservation policies and funding to prioritize these high-impact areas.

"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," said Dr. Mitchell.