According to recent research led by the University of Colorado Boulder, streamflow in Alaskan rivers is increasing throughout both the spring and fall seasons, owing mostly to rising air temperatures over the last 60 years.
This increased volume of free-flowing water during the shoulder seasons is exacerbated by earlier snowmelt and thawing permafrost, both of which are being influenced by rising temperatures; all of which are influencing the formation and safety of Alaska river ice in winter, as well as the timing of when rivers “break up” in response to seasonal warming each spring.
The findings are the result of a collaboration between researchers at CU Boulder, the United States Geological Survey (USGS), and the National Park Service, who analyzed data from 1960 to 2019 for nine major river basins in Alaska. Their findings, published in Environmental Research Letters in February, demonstrate how rivers can be used to quantify the cumulative effects of climate change in Arctic regions.
“Measuring rivers is useful because it integrates all these other changes in temperature, precipitation, permafrost, and snow cover. All the dynamics that feed the hydrologic cycle eventually get filtered into the amount of water in a river,” said Dylan Blaskey, lead author on the study and doctoral student in civil engineering.
This scientific work quantifies the consequences that local Indigenous communities that rely on these rivers for their livelihoods have already observed and experienced for generations. They confront not just cultural and economic losses as a result of less reliable winter river ice, but also increased hazard when using these rivers for transportation and fishing.
The CU-led research group sponsored the Arctic Rivers Summit in Anchorage late last year, ahead of the study’s publication. Indigenous leaders and community representatives, as well as government officials and scientists, gathered to discuss these and other serious concerns confronting Alaska and other Arctic communities.
At the Summit, the team learned more about regional and local concerns and observations. The conclusion is meant to assist researchers in tailoring and improving the dissemination of scientific data in order to generate knowledge and products useful for Indigenous people facing uncertain futures.
“We’re using these river gages to monitor these remote areas, but there are many people who have a much more intimate and holistic knowledge of the landscape and how it’s changing,” said Blaskey. “At the Summit, it became clear that we were converging on an understanding of how climate change is affecting Indigenous communities and Arctic ecosystems.”
The shrinking of the fall and spring seasons affects how long river ice persists and is safe to travel over. Indigenous communities have suffered an increasing number of fatalities over the last few decades. It seemed that everyone at the workshop had stories of someone who had fallen in the ice and lost their life.
Keith Musselman
Strides in streamflow
In comparison to the Lower 48, there are very few river gages in Alaska, said CU Boulder co-author Keith Musselman, assistant professor at the Institute of Arctic and Alpine Research (INSTAAR) at CU Boulder.
The researchers compared streamflow to air temperature, soil temperature, soil moisture, and precipitation across nine Alaskan rivers over six decades of monthly data from river gages. They also accounted for large scale climate anomalies, such as El Niño and La Niña.
Streamflow in Alaskan rivers often peaks in the summer and falls dramatically in the winter, with sharp contrasts between the two seasons. The study discovered that, while the volume of water flowing through these rivers does not change on an annual basis, when it runs through them does, with more water freely flowing from October to April, resulting in more gradual seasonal shifts.
Changes in air temperature have had the biggest impact on streamflow in these Alaskan rivers. The average days above freezing in April and October have increased by about a day every decade, according to Blaskey. These months are also when the average monthly streamflow has increased the most: by 15% per decade in April and 7% per decade in October.
They also found that the correlation of increased streamflow with temperature is only getting stronger over time when data from the first 30 years (1960-1989) are compared to the most recent 30-year period (1990-2019).
Since the 1960s, winter air temperatures have increased by 7.2 degrees Fahrenheit (4 degrees Celsius) on average across the global Arctic. The findings from Alaskan river gages contribute to quantifying the disproportionate effects of climate change on the planet’s northernmost ecosystems.
“One of the opportunities and challenges of researching in Alaska is that signals of climate change have already begun to appear,” said Blaskey.
Ripple effects in community
Indigenous populations rely on rivers for transportation and food, whether they are frozen or running. Many rivers are traditional hunting and fishing routes that can be crossed when they are frozen. Because Alaska’s road networks are limited, rivers also serve as vital thoroughfares for connecting communities and bringing in seasonal supplies such as fuel and food.
As the seasons shift, ice freezes later and breaks up earlier, undermining the stability and safety of river ice.
“The shrinking of the fall and spring seasons affects how long river ice persists and is safe to travel over. Indigenous communities have suffered an increasing number of fatalities over the last few decades,” said Musselman. “It seemed that everyone at the workshop had stories of someone who had fallen in the ice and lost their life.”
These and other timely concerns were shared at the Arctic Rivers Summit in December. Hosting this conference gave Blaskey and his colleagues another opportunity to listen to the communities most affected by the changes they’re examining, in addition to working with an Indigenous advisory council who has helped guide their work since the project’s beginning.
“Documenting the long-term changes in streamflow is a way for us to quantify and share what’s happening in the rivers,” said Blaskey. “Indigenous communities already know what’s happening to the rivers.”
“Together, Indigenous knowledge and long-term monitoring can help to develop narratives of change across the Arctic landscape to support planning and community adaptation,” said Musselman.
