Arctic river channels migrating slower due to warming climate: study

By James Gamble via SWNS

Arctic rivers are moving and changing at a slower pace than expected due to climate change, suggests a new study.

Scientists believed that, like most other rivers in the world, warming climates would cause the ways in which Arctic river banks change and are eroded to accelerate.

However, a new study from the University of British Colombia in Canada suggests warming climates over the past half a century have caused rivers in the Arctic to 'migrate' at a slower pace.

The researchers believe the "greening up" of the rivers' banks may have led to the slowing of sideways migration of around 20 percent over the past half a century.

The study team added that understanding these rivers' responses to changes in the environment is 'paramount' to assessing the impacts of climate change on the Arctic.

Migration refers to the natural process of how a river channel moves over time.

The process can occur gradually, such as when a stream erodes away one bank and deposits sediment along the opposite side or quickly during floods and high waters.

The UBC team sought to test the hypothesis that our warming climate leads to faster channel migration in Arctic rivers.

To do this, they analyzed a collection of time-lapsed satellite images of the past 50 years.

They compared more than 1,000 kilometers of riverbanks from ten Arctic rivers in Alaska, the Canadian Yukon and Northwest Territories, including major watercourses such as the Mackenzie, Porcupine, Slave, Stewart and Yukon rivers.

They had expected to find that the meandering waterways in permafrost terrain - terrain which has been frozen for two or more years - were moving faster due to the warming climate.

As part of their research, the scientists also analyzed data from rivers in non-permafrost regions of warmer climates in the Americas, Africa and Oceania.

They found that these rivers tend to migrate at faster rates in their warming climates, which is more consistent with previous studies.

But in Arctic rivers, the researchers were surprised to find that the opposite was true.

The time-lapse analysis showed migration of large Arctic rivers has decreased by around 20 percent over the past 50 years - and the study's authors claim this could even be a "conservative measure."

Dr. Alessandro Ielpi, the lead author of the study, explained that the assumption of faster channel migration across all rivers due to climate change had dominated the scientific community for years.

Dr. Ielpi, also an Assistant Professor with UBC Okanagan’s Irving K. Barber Faculty of Science, said: "The western Arctic is one of the areas in the world experiencing the sharpest atmospheric warming due to climate change.

“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.

"But the assumption had never been verified against field observations.

"We tested the hypothesis that large sinuous rivers in permafrost terrain are moving faster under a warming climate and we found exactly the opposite.

“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.

"Surprisingly, these rivers migrate at slower rates under warming temperatures."

Dr. Ielpi added that an increase in vegetation has helped to stabilize the riverbanks.

He said: “Yes, permafrost is degrading, but the influence of other environmental changes, such as the 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 dynamics of these rivers reflect the extent and impact of global climate change on sediment erosion and deposition in Arctic watersheds.

“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 highlighted that monitoring the erosion of riverbanks and channel migration around the world is an important tool for better understanding the effects of climate change.

“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.

"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 was published in the scientific journal Nature Climate Change.