River ice phenology across Alaska: Geospatial patterns and temporal change

Abstract River ice is a vital component of the cryosphere, influencing hydrology, ecology, and society. When adequately thick and stable, river ice serves as a key transportation corridor for residents of remote Arctic and sub-Arctic communities. Climate change is altering the timing, extent, and duration of river ice cover, impacting both environmental processes and human activities. This study examines regional variability and temporal change in river ice phenology across Alaska using satellite observations and climate-driven modeling. We extracted reach-scale surface water extent from the Landsat archive to characterize river ice cover at sub-monthly time scales, capturing spatial heterogeneity and seasonal transitions during freeze-up and break-up. We then developed statistical models driven by ERA5-Land climate reanalysis to reconstruct annual metrics identifying the beginning, end, and duration of ice-covered conditions from water years 1979–2023. Model results show that typical river ice duration varied strongly along climatic gradients, ranging from 2.4 months in a southern coastal region to 7.3 months in northern Alaska (2000–2023). Decadal comparisons show that river ice duration during 2014–2023 was substantially shorter than in the 1980s across much of the state, with reductions exceeding three weeks within western and southwestern Alaska. These recent declines reflect the combined influence of delayed freeze-up and, to a lesser extent, earlier break-up onset. Long-term trend analyses (1979–2023) reveal persistent declines in ice duration, primarily driven by later freeze-up, with rates of change from 3–5 d decade −1 where trends are significant. Together, these findings demonstrate substantial, regionally structured changes in Alaska’s river ice regimes and underscore growing challenges in transportation, public safety, and access in river-dependent communities.