An international team of researchers monitoring the impact of climate change on large rivers in the Canadian Arctic and Alaska have determined that as the region warms sharply, its rivers are not moving as scientists expected.
Dr. Alessandro Ielpi, Adjunct Professor at the Irving K. Barber School of Science at the University of British Columbia (UBC) Okanagan, Canada, who is a landscape designer and lead author of the study published in the journal Nature Climate Change (1)ensures that the results were surprising”.
The research, carried out with Dr. Mathieu Lapôtre, from Stanford University (United States); Dr Alvise Finotello, from the University of Padua, Italy, and Dr Pascale Roy-Léveillée, from Laval University, examine how global warming is affecting arctic rivers that flow through permafrost terrain.
“The western Arctic is one of the parts of the world that is experiencing the most pronounced global warming due to climate change,” says Ielpi. “Many scientists in the north predicted that rivers would be destabilized by atmospheric warming. The idea was that, As permafrost thaws, riverbanks weaken and thus northern rivers are less stable and are expected to reposition their beds at a faster rate.”
This assumption of faster stream migration due to climate change has dominated the scientific community for decades. “But it had never been checked against observations on the ground,” he adds.
Satellite images taken over 50 years ago
To verify this, the team analyzed a collection of satellite images taken more than 50 years ago. They compared more than 1,000 kilometers of banks of 10 arctic rivers in Alaska, the Yukon, and the Northwest Territories, including major watercourses such as the Mackenzie, Porcupine, Slave, Stewart, and Yukon.
“We tested the hypothesis that large winding rivers in permafrost terrain move faster under a warming climate and found the exact opposite,” he explains. “And yes, the permafrost is degrading, but the influence of other environmental changes, such as the greening of the Arctic, counteract their effects Rising temperatures and humidity in the Arctic mean the region is greening Shrubs are expanding, thickening and taller in areas that previously had little vegetation”.
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,” the researchers write. “Understanding the behavior of these rivers in response to environmental changes is paramount to understanding and working with the impact of global warming in the Arctic regions”.
Dr. Ielpi notes that tracking riparian erosion and stream migration across the globe is an important tool that should be widely used to understand climate change.
As part of this research, a dataset of rivers located in regions without permafrost and representative of warmer climates in the Americas, Africa and Oceania was also analyzed. Those rivers migrated at rates consistent with those recorded in previous studies, unlike those in the Arctic.
Rivers migrating at slower rates under warmer temperatures
“We found that large, meandering rivers with varying degrees of permafrost distribution in their floodplains and catchments, instead show a peculiar range in migration rates,” Ielpi said. “Surprisingly, these rivers migrate at slower rates.” under warmer temperatures.”
Chronological analysis shows that lateral migration of the great winding rivers of the Arctic has decreased by about 20% in the last half century.
“The slowdown in migration of around 20% of documented Arctic watercourses in the last half century is an important signal on a continental scale. And our methodology tells us that 20% may very well be a conservative measure,” he stresses. –. We are confident that it can be linked to processes such as scrubbing and permafrost thawing, which in turn are related to global warming.”
“Scientific thinking often evolves through incremental discoveries, although great value lies in disruptive insights that force us to look at an old problem with new eyes,” Ielpi said. “We sincerely hope that our study will encourage landscape scientists and climate elsewhere to reassess other basic assumptions that, when put to the test, can reveal fascinating and exciting facets of our ever-changing planet.”
- (1) Large sinuous rivers are slowing down in a warming Arctic. Nature Climate Change.