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 (ERA5) and river discharge observation (USGS NWIS) 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 days 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 to 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.

Coupled high-resolution land-atmosphere modeling for hydroclimate and terrestrial hydrology in Alaska and the Yukon River Basin (1990-2021)

“…Mean annual and seasonal air temperatures are increasing statewide with the largest warming signal detected in winter (Bieniek et al, 2014;Stafford et al, 2000). In response to warming, we have observed a large increase in the extent of permafrost degradation (Jorgenson et al, 2006;Lawrence & Slater, 2005;Osterkamp & Romanovsky, 1999;Saito et al, 2020), a shifted annual snow cycle and earlier snowmelt (Cox et al, 2017;Musselman et al, 2021;Stone et al, 2002), as well as increasing cold season discharge in Alaskan rivers (Blaskey et al, 2023;Gudmundsson et al, 2019). These hydroclimatic changes are deteriorating the quality of river ice roads and corresponding transportation safety, affecting terrestrial and aquatic ecosystems, and disproportionately increasing threats to Indigenous Alaskans, especially those who practice subsistence living (Knoll et al, 2019;McNeeley & Shulski, 2011).…”

Hydrology Controls Dissolved Organic Carbon and Nitrogen Export and Post‐Storm Recovery in Two Arctic Headwaters

“…Despite rapid changes to high‐latitude ecosystems evident in changing river chemistry, research efforts in Arctic rivers have lagged behind those in temperate regions (Laudon et al., 2017). The spring snowmelt and mid‐season storm events are predicted to become more intense (Blaskey et al., 2023; Dou et al., 2022), resulting in seasonal and interannual changes in the magnitude of C and N transported from Arctic headwaters. In recent years, optical sensors have provided a useful tool to help quantify additional solutes of interest (Burns et al., 2019; Crawford et al., 2015; Pellerin et al., 2016; Rode et al., 2016).…”

Seasonal and decadal subsurface thaw dynamics of an Aufeis feature investigated through numerical simulations

“…Although the specific effects on river corridor dynamics is uncertain, the changes are likely to lead to warmer river water temperatures, which implies permafrost melt, active layer thickening, and talik deepening, all of which increases the volume of subsurface liquid water available to discharge to the surface. Warming river temperatures and increasing winter river discharge are ongoing throughout Alaska and especially on the North Slope (Blaskey et al, 2023). Many springs in northern Alaska have not shown a temperature increase between 1975 and 2021 (Koch et al, 2024), suggesting that the source of water to the aufeis fields may not warm in the near future.…”