Climate change is transforming Arctic rivers in unexpected ways

The Arctic is warming faster than the global average and scientists have been measuring the effects. While most research has focused on melting permafrost, retreating glaciers and shrinking sea ice, it is likely that the rivers are also changing. The Arctic is home to many large rivers that carry water from the seasonal melting of glaciers and ice, so it is likely that they will be affected by atmospheric temperature changes. 

An international team of researchers has now conducted an investigation into the impact of climate change on large rivers in Arctic Canada and Alaska. The experts analyzed a collection of time-lapsed satellite images of river courses stretching back 50 years and compared the changes. The images covered more than a thousand kilometers of riverbanks along the edges of 10 large Arctic rivers in the Yukon and Northwest Territories of Canada, as well as in Alaska. These watercourses included the Mackenzie, Porcupine, Slave, Stewart and Yukon.

Study lead author Dr. Alessandro Ielpi is an assistant professor with the University of British Colombia Okanagan’s Irving K. Barber Faculty of Science. The research was conducted with Dr. Mathieu Lapôtre at Stanford University, Dr. Alvise Finotello at the University of Padua in Italy, and Université Laval’s Dr. Pascale Roy-Léveillée.

The researchers, who aimed to understand how atmospheric warming is affecting Arctic rivers that flow through the permafrost, were somewhat surprised by the results they obtained. 

“The western Arctic is one of the areas in the world experiencing the sharpest atmospheric warming due to climate change,” said Dr. Ielpi. “Many northern scientists predicted the rivers would be destabilized by atmospheric warming. The understanding was that as permafrost thaws, riverbanks are weakened, and therefore northern rivers are less stable and expected to shift their channel positions at a faster pace.”

Although this assumption of faster channel migration due to climate change has dominated the scientific community for decades, it has never been tested in the field. Dr. Ielpi and his colleagues designed their research to identify exactly how the river courses have changed over the past five decades.

“We tested the hypothesis that large sinuous rivers in permafrost terrain are moving faster under a warming climate and we found exactly the opposite,” he said. “Yes, permafrost is degrading, but the influence of other environmental changes, such as greening of the Arctic, counteracts its effects. Higher temperatures and more moisture in the Arctic mean the region is greening up. Shrubs are expanding, growing thicker and taller on areas that were previously only sparsely vegetated.”

The increased river bank vegetation, or shrubification, has had the effect of stabilizing the banks and reducing the rate at which they shift, even though the frozen ground around the river banks is slowly melting. 

“The dynamics of these rivers reflect the extent and impact of global climate change on sediment erosion and deposition in Arctic watersheds,” wrote the study authors. “Understanding the behavior of these rivers in response to environmental changes is paramount to understanding and working with the impact of climate warming on Arctic regions.”

Dr. Ielpi stresses the importance of monitoring riverbank erosion and channel migration around the globe, not only in the Arctic. This method can be used to understand the effect of climate change on rivers everywhere. As part of the current research, a dataset of rivers found in non-permafrost regions and representative of warmer climates in the Americas, Africa and Oceania was also analyzed. Those rivers migrated at rates consistent with what was reported in previous studies, unlike the rivers studied in the Arctic.

“We found that large sinuous rivers with various degrees of permafrost distribution in their floodplains and catchments, display instead a peculiar range in migration rates,” said Dr. Ielpi. “Surprisingly, these rivers migrate at slower rates under warming temperatures.”

The time-lapse analysis showed that the sideways migration of large, sinuous Arctic rivers has decreased by about 20 percent over the last half-century.

“The migration deceleration of about 20 percent of the documented Arctic watercourses in the last half century is an important continent-scale signal. And our methodology tells us that 20 percent may very well be a conservative measure,” explained Dr. Ielpi. “We’re confident it can be linked to processes such as shrubification and permafrost thaw, which are in turn related to atmospheric warming.”

“Scientific thinking often evolves through incremental discoveries, although great value lies in disruptive ideas that force us to look at an old problem with new eyes. We sincerely hope our study will encourage landscape and climate scientists elsewhere to re-evaluate other core assumptions that, upon testing, may reveal fascinating and exciting facets of our ever-changing planet.”

The study is published in the journal Nature Climate Change.

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By Alison Bosman, Earth.com Staff WriterCheck us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.