Alaska's Rivers Are Flowing More in the Cold Season

Warmer Octobers and Aprils have helped push up cold-season river flow across Alaska. Image from the NPS's page.

A water cycle in transition

Arctic and boreal watersheds are changing dramatically as the region's climate warms fast. Shifting snowpack, changing precipitation and thawing permafrost are among the factors altering how water moves through them and how their rivers flow. Across the Arctic, snow melts earlier, permafrost is degrading, the active layer is deepening and there is less river ice — all expected to change how streams flow through the year.

The study

Scientists from the University of Colorado, the U.S. Geological Survey and the National Park Service analyzed long-term river discharge records — more than 60 years of them — from across Alaska, alongside long-term climate reanalysis data. The rivers varied in size and region, from the Kuparuk River on the North Slope to the Kenai River in Southcentral Alaska.

What they found

• The cold season: the most dramatic changes came between October and April, when flow rose 10% per decade.
• April, the month most rivers' ice breaks up, saw the most widespread increase: 15% per decade.
• October, when river ice usually begins to form: 7% per decade.
• Warmer shoulder seasons: rising air temperatures in October and April added 1.1 days above freezing per decade. Snow ablation rose 20% per decade, and snow water equivalent fell 12% per decade.
• A tighter link: comparing 1960–1989 with 1990–2019, the correlation between air temperature and monthly discharge rose from 0.33 to 0.68 for April and from 0.0 to 0.48 for October — showing that recent warming is directly tied to the change in flow.

Why it's happening

• Fall: warmer temperatures delay freeze-up, letting more groundwater reach the river channel.
• Spring: warming brings earlier snowmelt, and with it rising discharge in April and May.

Why it matters

The shift is a consequence of climate change acting on the water cycle of northern regions. It has important consequences for biogeochemical cycling and freshwater food webs — and increases this widespread show the scale at which water and chemical flows are being altered across the Arctic.

Sources

Based on "Alaska river flow is increasing during the cold season," National Park Service, summarizing D. Blaskey, J. C. Koch, M. N. Gooseff, A. J. Newman, Y. Cheng, J. A. O'Donnell and K. N. Musselman, "Increasing Alaskan river discharge during the cold season is driven by recent warming," Environmental Research Letters 18(2): 024042 (2023); published by the National Park Service and in the public domain; rewritten in hubnx's own words.