A team of international researchers monitoring the impact of climate change on large meandering rivers in Arctic Canada and Alaska determined that as the region is sharply warming up, its rivers are not moving as scientists have expected.
The research, which examines how atmospheric warming is affecting Arctic rivers flowing through permafrost terrain, appeared this week in Nature Climate Change. It was the result of a collaboration with Alessandro Ielpi, an assistant professor with the University of British Columbia Okanagan, Mathieu Lapôtre at Stanford University, Alvise Finotello at the University of Padua in Italy, and Pascale Roy-Léveillée at Université Laval.
“The western Arctic is one of the areas in the world experiencing the sharpest atmospheric warming due to climate change,” Ielpi said. “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.”
This assumption of faster channel migration owing to climate change has dominated the scientific community for decades – but it hadn’t been verified with field observations, Ielpi said.
To test this assumption, the study authors analyzed a collection of time-lapsed satellite images stretching back more than 50 years. They compared more than 600 miles of riverbanks from 10 Arctic rivers in Alaska and the Yukon and Northwest Territories, including major watercourses like the Mackenzie, Porcupine, Slave, Stewart, and Yukon.
“We went into this project thinking we’d quantify how much the lateral migration of Arctic rivers has accelerated due to atmospheric warming over the past 50 years,” said Lapôtre, an assistant professor of Earth and planetary sciences in the Stanford Doerr School of Sustainability. “We were quite shocked by what we found instead.”
Rather than the expected acceleration, they found that the sideways migration of large Arctic rivers actually slowed down by about 20 percent over the past half century.
“Whereas one might think that slowing Arctic rivers might be good news, as it may imply slower release of organic carbon stored in floodplains to the oceans, this change in river dynamics is bound to have other repercussions on geochemical cycling and Arctic ecosystems,” Lapôtre said.
Through remote sensing, the researchers linked the slowdown in river migration to a progressive “greening” of Arctic riverbanks as permafrost thaws. This growing and robust vegetation along the riverbanks means the banks have become more stable.
“The dynamics of these rivers reflect the extent and impact of global climate change on sediment erosion and deposition in Arctic watersheds,” the researchers state in the paper. “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.”
As part of this 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 those in the Arctic.
“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,” Ielpi said. “We’re confident it can be linked to processes such as shrubification and permafrost thaw, which are in turn related to atmospheric warming.”
Monitoring riverbank erosion and channel migration around the globe is an important tool that should be widely used to understand climate change, according to Ielpi. The study authors also hope this research will encourage other scientists to reevaluate core assumptions about the planet.
“Our perhaps counterintuitive finding, to me, is a perfect illustration of the complexity of the Earth system, and really highlights the need to integrate knowledge across the geological, atmospheric, and biological sciences to better understand our planet’s dynamics and mitigate our impact,” Lapôtre said.
This story was adapted from a press release originally issued by the University of British Columbia Okanagan.
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