Alaska river flow is increasing during the cold season

Warming air temperatures during the shoulder seasons of October and April contributed to a 10% per decade increase in river flow across Alaska.

Arctic and boreal watersheds are undergoing dramatic changes due to rapid climate change in the region. Changing snowpack, precipitation, and permafrost thaw are just some of the factors contributing to shifts in watershed hydrology and river flows. To evaluate changes in river flow, scientists from the University of Colorado, U.S. Geological Survey, and the National Park Service analyzed long-term (>60 years) discharge records from across the state of Alaska. Rivers varied in size and region, from the Kuparuk River on the North Slope of Alaska to the Kenai River in Southcentral Alaska. The most dramatic changes in river discharge occurred during the cold months, between October and April, with flow increasing by 10% per decade. Using climate data, the researchers determined that warming air temperatures during the shoulder seasons of October and April contributed to this increase in river flow. During fall, warmer temperatures are delaying freeze-up and allowing for more groundwater inputs to the river channel. During spring, warming can cause earlier snowmelt and consequently, rising discharge in the months of April and May. This shift in river flow across Alaska is a consequence of the effects of climate change on the water cycle of northern regions, and has important consequences for biogeochemical cycling and freshwater food webs.

Increasing Alaskan river discharge during the cold season is driven by recent warming

Abstract

Arctic hydrology is experiencing rapid changes including earlier snow melt, permafrost degradation, increasing active layer depth, and reduced river ice, all of which are expected to lead to changes in stream flow regimes. Recently, long-term (>60 years) climate reanalysis and river discharge observation data have become available. We utilized these data to assess long-term changes in discharge and their hydroclimatic drivers. River discharge during the cold season (October-April) increased by 10% per decade. The most widespread discharge increase occurred in April (15% per decade), the month of ice break-up for the majority of basins. In October, when river ice formation generally begins, average monthly discharge increased by 7% per decade. Long-term air temperature increases in October and April increased the number of days above freezing (+1.1 d per decade) resulting in increased snow ablation (20% per decade) and decreased snow water equivalent (−12% per decade). Compared to the historical period (1960-1989), mean April and October air temperature in the recent period (1990-2019) have greater correlation with monthly discharge from 0.33 to 0.68 and 0.0-0.48, respectively. This indicates that the recent increases in air temperature are directly related to these discharge changes. Ubiquitous increases in cold and shoulder-season discharge demonstrate the scale at which hydrologic and biogeochemical fluxes are being altered in the Arctic.

Blaskey, D., J. C. Koch, M. N. Gooseff, A. J. Newman, Y. Cheng, J. A. O'Donnell, and K. N. Musselman. 2023. Increasing Alaskan river discharge during the cold season is driven by recent warming. Environmental Research Letters 18(2): 024042.