Wetlands Set the Pace of runoff in Northern Great Plains

On the vast Prairie landscape, water does not move in straight lines or on a predictable schedule. Some years, rivers stay quiet despite heavy precipitation. In others, they surge suddenly, overwhelming banks and spilling across fields.

New research suggests the answer to this unpredictability lies not just in the sky, but on the ground and hidden in millions of wetlands scattered across the Prairie Pothole Region.

A study published in Communications Earth & Environment entitled Wetlands set the pace of annual runoff in the northern Great Plains, co-authored by Ducks Unlimited Canada (DUC) research scientist Pascal Badiou, Ali Ameli and Javad Rahmani from the University of British Columbia and Irena Creed from the University of Toronto (Scarborough Campus), reveals that wetlands play a decisive role in determining how water moves across the Prairies.

More Than Just Water on the Landscape

For decades, wetlands have often been seen as passive features and places where water collects after rain or snowmelt. But this research tells a very different story.

Wetlands, it turns out, actively regulate water. They store it, release it and influence how much flows downstream in any given year.

Across the Prairie Pothole Region, wetlands influence not only flood risk, but also drought resilience and water quality. Their condition, including how full they are at any given time, can determine whether a storm becomes a minor event or a major runoff episode.

A Landscape Measured Over Time

To understand this relationship, researchers examined nearly four decades of satellite imagery alongside streamflow data from 109 watersheds across Canada and the United States.

They wanted to answer a deceptively simple question: what drives year-to-year changes in runoff? Is it events like rainfall, snowfall and aridity, or is it something else?

In nearly 70 percent of the watersheds studied, the answer pointed clearly to wetlands.

Climate still matters but largely because it governs how full wetlands become, rather than directly controlling how water flows through the system.

“Fill and Spill” Moments

One of the most striking insights from the study is how wetlands behave under different conditions.

In dry periods, they absorb and store water, keeping runoff low. As conditions get wetter, wetlands begin to fill. Once their storage capacity is reached, they spill over and runoff can increase more quickly.

Landscapes with more wetlands have greater storage capacity, allowing them to hold more water before runoff begins to increase.

Small Wetlands, Oversized Impact

Perhaps the most surprising finding is the role of geographically isolated wetlands—the numerous small wetlands dotted across the landscape, embedded in grasslands, cropland, or forest. Often overlooked in land-use decisions, these features proved to be among the most powerful regulators of water, especially when there are many in a given area.

Watersheds with more of these isolated, smaller wetlands showed stronger flood buffering, lower average runoff and greater stability in extreme conditions.

In other words, even the smallest wetlands can make a meaningful difference, shaping how the entire system responds to both wet and dry years.

Rethinking Flood Risk

The study also challenges the common assumption that flood risk is driven primarily by large storms.

Instead, researchers found that extreme rainfall only leads to major runoff when wetlands are already full.

This means flood risk begins long before a storm arrives. As wetlands fill over the course of a season, the flood risk builds until the landscape reaches a tipping point.

What Happens When Wetlands Disappear

As wetlands are drained or altered, that natural buffering system begins to break down.

Without wetlands to store water, the landscape becomes more reactive. Rain and snowmelt move more quickly downstream, increasing flood risk. At the same time, less water is retained on the landscape, reducing resilience during drought and accelerating the movement of nutrients through the system.

These changes are not just ecological; they affect communities, infrastructure and long-term water security across the Prairies.

A Stronger Case for Conservation

For Ducks Unlimited Canada, the findings add powerful new evidence to a long-standing message: conserving wetlands is one of the most effective ways to manage water on the landscape.

Wetlands are more than simply habitat—they are natural infrastructure that help make communities resilient, stabilize water flows and help the Prairies adapt to an increasingly variable climate.

As this research shows, when we conserve wetlands, we are not just helping ecosystems. We are investing in resilience for wildlife, water and the people who depend on both.