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Flooding is one of Canada’s most frequent natural hazards, and with climate change driving more extreme rainfall events, the need for effective flood prevention strategies is more urgent. Matthew Mitchell‘s new research highlights the crucial role of Canada’s natural ecosystems. For the first time, researchers have conducted a national-scale analysis to identify the ecosystems that provide essential flood-prevention benefits. We spoke with Dr. Mitchell to learn how natural ecosystems not only capture runoff but also shield millions of Canadians from the impacts of flooding, and learn what this means for conservation efforts, policy, and community action.

Can you tell us about this new research?

We assessed the benefits that Canada’s natural ecosystems provide for flood prevention, the first time an analysis like this has been done at a national scale. We identified the natural ecosystems across the country that capture and retain the highest amounts of runoff and are simultaneously located upstream of urban and agricultural areas, particularly those located in floodplains. The most important of these natural ecosystems help prevent flooding in 54% of urban areas and 74% of agricultural lands within floodplains. This benefits approximately 3.7 million people or 10% of the Canadian population directly that lives in these areas. Our study highlights the importance of natural ecosystems in protecting Canadians from flooding and where restoration or conservation actions could best improve this.

Your paper highlights the importance of “service providing areas” and “service demanding areas” for flood prevention. What are these concepts and their significance in your study?

One of the biggest complexities we had to grapple with in our study is the fact that water runs downhill! We therefore had to understand all of the upstream/downstream connections that exist within and between watersheds to properly assess how a particular forest or wetland prevents flooding downstream. In our study, “service providing areas” are those areas of natural vegetation that can provide flood prevention by retaining runoff and rainfall. Conversely, “service demanding areas” are urban and agricultural areas, and especially those located within floodplains, that can most benefit from flood prevention. When you have the situation where a “service providing area” is located upstream of a “service demanding area,” then flood prevention can happen. The word “service” in all of this comes from “ecosystem service” which is a scientific term that refers to the benefits that people receive from natural ecosystems.

We’ve seen some pretty serious flooding events in the lower mainland this fall. How does this new research factor into the broader picture of flood prevention?

Flooding, by some measures, if the most frequent natural hazard in Canada, and is likely to become even more frequent due to climate change and increasing extreme rainfall events. Our research highlights and emphasizes the importance of natural ecosystems in safeguarding people and infrastructure in Canada from flooding. Taking advantage and increasing these Nature-based solutions to climate change, in combination with human-made infrastructure, has the potential to be a more cost-effective and resilient way to increase flood prevention benefits in BC and the Lower Mainland, as well as across Canada in the face of these challenges.

Your research indicates that about 10% of Canada’s flood-preventing natural ecosystems are particularly crucial. What characteristics make these ecosystems so vital, and where are they primarily located?

Not all natural ecosystems are created equally with respect to flood prevention. Trees and forests due to their dense foliage and deep roots are often able to capture and retain more rainfall and runoff than shrubs or grasses. In addition, ecosystems that are located in places with more rainfall have the opportunity to capture more runoff. The most critical flood-preventing natural ecosystems are those that, if they were removed, would result in a 50% or greater increase in runoff. This includes places like the Okanagan and interior valleys of British Columbia, northern Ontario from Lake Huron through to Ottawa and southern Quebec, and even northern areas around Great Slave and Great Bear Lake. These aren’t always the places with the most people or agriculture downstream, but can be places with remote and rural communities or critical transportation infrastructure that could be strongly impacted by flooding.

What are the broader implications of your findings for national conservation strategies and policies?

One key finding is that only 8% of the most important natural ecosystem for flood prevention are currently designated as protected. Considering that 13% of Canada’s terrestrial and freshwater area is protected or conserved, this indicates we need to do a better job protecting those areas that prevent floods. The best way to do this might not always be by creating parks though, other conservation measures such as the creation of riparian buffers in agricultural lands, incentivizing landowners and tenure-holders to maintain key upstream ecosystems, and Indigenous Protected and Conserved Areas are also likely to be key.

Beyond policymakers and can the community do with this information to help prevent flooding?

While our national-scale analysis won’t always be able to directly inform local-scale decisions, what it does do is highlight the importance of nature-based solutions to increasing flood risk. Communities can use this information to advocate for the protection of key natural ecosystems and lobby governments to integrate these types of solutions into their flood prevention strategies alongside traditional infrastructure like levees, dikes, and reservoirs. There are also smaller-scale nature-based solutions like rain gardens and bioswales that are appropriate for urban settings and that can be implemented by individual property owners of community groups.