Climate change slows movement of large Arctic rivers

Scientists have long believed that rapid warming in the Arctic would cause river channels to move faster, but a new study has found the opposite may be true for large, winding rivers in the region.

The paper, published in the scientific journal Nature and Climate Change, details how an international team of researchers tested this theory by analyzing satellite imagery of rivers in Alaska, Yukon and the Northwest Territories over time.

They found migration rates of these rivers, rather than increasing, decreased overall by about 20 per cent between 1972 and 2020.

"My reaction was 'oh boy, it's going to be hard to convince people about this,'" lead author Alessandro Ielpi said of the findings.

"It's potentially a disruptive idea. It may potentially reshape the way we think about northern environments and the way they are adapting to the changing climate."

Ielpi, an assistant professor in the Department of Earth, Environmental and Geographic Sciences at the University of British Columbia-Okanagan, said it has been "almost a core belief" among the scientific community that rising temperatures and permafrost thaw would speed up the rate that rivers change position.

"Think about trying to dig a hole in ground that is frozen. Of course, you'll spend more energy and it's going to be more demanding than digging or eroding soil that is not frozen," he explained.

"If the temperature goes up and the frozen ground is progressively melting, the reverse would have found less resistance to erosion."

Scientists have theories about why migration of these rivers has instead slowed over the past five decades -- chiefly Arctic greening.

While increasing temperatures and moisture in the Arctic have resulted in permafrost thaw, they have also led to shrubification, where shrubs are growing thicker and taller in areas that were once barren or sparsely vegetated.

Ielpi said the increased vegetation is causing riverbanks to be more stable and less susceptible to erosion, and the plants are also reducing surface run-off by using water.

The study focuses on 10 sinuous rivers wider than 100 metres in permafrost terrain, including the Mackenzie, Porcupine, and Yukon rivers. Its authors caution the findings may not apply to smaller streams in upland catchments, as they may respond differently to increasing temperatures.

"More data from the ground and more studies are going to be needed in the coming years to corroborate this interpretation," Ielpi said.

He said the findings highlight the need to not "take anything for granted and always look for surprises."

He said they could also have implications for how Northern communities plan for the future.

This report by The Canadian Press was first published March 10, 2023.

This story was produced with the financial assistance of the Meta and Canadian Press News Fellowship.