A group of international researchers monitoring the effects of climate change on huge rivers in arctic Canada and Alaska have found that despite rapid warming in the region, the rivers are not flowing as scientists predicted.
Landscape architect Dr Alessandro Ielpi is an Assistant Professor in the Irving K. Barber Faculty of Science at UBC Okanagan. He is also the lead author of a paper just published in Nature Climate Change. The study, carried out in collaboration with Dr. Mathieu Lapotrem of Stanford University, Dr. Alvis Finotello from Padua, Italy and Dr. Pascale Roy-Leveillee of the University of Laval, investigates how atmospheric warming is changing Arctic rivers flowing through permafrost.
Their findings, says Dr. Ielpi, she was a little surprising. “The Western Arctic is one of the areas in the world experiencing the most rapid atmospheric warming due to climate change,” he says. “Many northern scientists predicted that rivers would be destabilized by a warming atmosphere.” It is understood that as the permafrost melts, the river banks are weakened and therefore the northern rivers are less stable and are expected to shift their channels more quickly.’
This assumption of faster channel migration due to climate change has dominated the scientific community for decades. “But this assumption has never been verified by field observations,” he adds.
To test this assumption, Dr. Ielpi and his team analyzed a collection of time-lapse satellite images – going back more than 50 years. They compared more than a thousand kilometers of riverbanks from 10 arctic rivers in Alaska, the Yukon and the Northwest Territories, including large watercourses such as the Mackenzie, Porcupine, Slave, Stewart and Yukon.
“We tested the hypothesis that large meandering rivers in permafrost terrain move faster in a warming climate and found the opposite,” he says. “Yes, permafrost is degrading, but the effects of other environmental changes, such as the greening of the Arctic, are counteracting its effects. Warmer temperatures and more humidity in the Arctic mean the region is turning green. The bushes are expanding, becoming stronger and taller in areas that were previously sparsely covered.”
This growing and robust vegetation along the banks means that the banks have become more stable. “The dynamics of these rivers reflect the extent and impact of global climate change on erosion and sediment deposition in Arctic watersheds,” writes Dr. Ielpi and his colleagues 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.”
Dr. Ielpi points out that monitoring river bank erosion and channel migration around the world is an important tool that should be widely used to understand climate change. As part of this research, a dataset of rivers found in areas without permafrost and representing warmer climates in the Americas, Africa and Oceania was also analysed. These rivers migrated at rates consistent with those reported in previous studies, unlike those in the Arctic.
“We found that large meandering rivers with varying degrees of permafrost distribution in their floodplains and catchments instead show a particular range of migration rates,” says Dr. Ielpi. “Surprisingly, these rivers are migrating more slowly as they warm.”
Time-lapse analysis shows that the lateral migration of the great meandering rivers of the Arctic has decreased by about 20 percent over the past half century.
“The slowdown in the migration of about 20 percent of documented Arctic water flows in the last half century is an important signal at the continental level. And our methodology tells us that 20 percent may very well be a conservative measure,” he says. “We believe this may be linked to processes such as bush and permafrost melting, which in turn are linked to atmospheric warming.
“Scientific thinking often develops through incremental discoveries, although great value lies in disruptive ideas that force us to look at an old problem with new eyes,” says Dr. Ielpi. “We sincerely hope that our study will encourage landscape and climate scientists elsewhere to reconsider other fundamental assumptions that, when tested, may reveal fascinating and exciting aspects of our ever-changing planet.”
