Lakes set in arctic permafrost landscapes can be susceptible to rapid drainage and downstream flood generation. Of many thousands of lakes in northern Alaska, hundreds have been identified as having high drainage potential directly to river systems and 18 such drainage events have been documented since 1955. In 2018 we began monitoring a large lake with high drainage potential as part of a long‐term hydrological observation network designed to evaluate impacts of land use and climate change. In early June 2022, surface water was observed flowing over a 30‐m wide bluff, with active headward erosion of ice‐rich permafrost soils apparent by late June. This overflow point breached rapidly in early July, draining almost the entire lake within 12 h and generating a 191 m3/s flood to a downstream creek. Water level and turbidity sensors and time‐lapse cameras captured this rapid lake‐drainage event at high resolution. A wind‐driven surface seiche and warming waters following ice‐out helped trigger the initial thermomechanical breach. We estimate at least 600 MT of lake sediment was eroded, mobilized, and transported downstream. A flood wave peaking at 42 m3/s arrived 14 h after the initial breach at a river gauge 9‐km downstream. Comparing this event with three other quantified arctic lake‐drainage floods suggests that lake surface area coupled with drainage gradient height can predict outburst flood magnitude. Using this relationship we estimated future flood hazards from the 146 lakes in the Arctic Coastal Plain of northern Alaska (ACP) with high drainage potential, of which 20% are expected to generate outburst floods exceeding 100 m3/s to downstream rivers. This fortunate and detailed drainage‐event observation adds to a growing body of research on the impact of lakes on arctic hydrology, hazard forecasting in a region with an increasing human footprint, and broader processes of landscape evolution in arctic lowlands.

Despite a long-term thinning trend in freshwater ice in northern Alaska, cold low-snow cover winters can still emerge to grow thick ice. In 2021, we observed abnormally thick ice by winter’s end on lakes and rivers throughout the Fish Creek Watershed in the National Petroleum Reserve in Alaska (NPR-A). This recent and anomalous winter presented an opportunity to assess how such conditions, more typical of many decades’ previous, affected aquatic habitat and winter water supply. Observed maximum ice thickness in 2021 of 1.9 m closely matched low-snow ice-growth simulations, whereas previous records averaged 1.5 m and more closely matched high-snow ice-growth simulations. The resulting extent of bedfast lake ice from late winter synthetic aperture radar (SAR) analysis in 2021 was the highest on record since 1992. This SAR analysis suggests a 33% reduction in liquid water below ice by lake surface area compared to the recent thin-ice winter of 2018 (1.2 m). Together these results help place the cold, low-snow winter of 2020-21 in context of the long-term trend toward warmer, snowier winters that appear to becoming more common in arctic Alaska.

Objective Within areas of Alaska, Humpback Whitefish Coregonus pidschian are an important subsistence resource for many Alaska Native communities. Recently, Humpback Whitefish in the upper Tanana River drainage were reported to be smaller at a given age and reach smaller maximum sizes than fish sampled 20 years ago. The objective of this study was to identify the factors that influence annual growth of Humpback Whitefish within the upper Tanana River drainage based on an analysis of otolith increments. Methods A series of mixed‐effects models were used to determine the relative importance of biotic (i.e., age, age at capture) and abiotic (i.e., year, sampling time period) factors on the growth of Humpback Whitefish. Juvenile (<5 years of age) and mature (≥5 years of age) growth periods were examined separately due to the unique habitats occupied by each life stage. Climate variables were correlated with the mature Humpback Whitefish biochronology to assess environmental drivers of adult growth. Result Biochronologies spanning over three decades (1982–2018) revealed patterns of variation in Humpback Whitefish otolith growth across years. A negative temporal trend spanning the entire study period was evident for juvenile growth, while a mostly positive trend was observed for mature growth. Between time periods, otolith growth was significantly different from zero for juvenile (estimate: −0.087; 95% CI = −0.151 to −0.023) but not mature (estimate: −0.030; 95% CI: −0.092 to 0.032) growth periods. Several environmental factors were positively (i.e., mean monthly temperature, growth degree days) and negatively (e.g., snow depth) correlated with the mature Humpback Whitefish biochronology. However, the model with mean April snow depth was the best‐performing environmental model. Conclusion These results suggest years with elevated snow depths negatively impact mature Humpback Whitefish growth. Cumulatively, these results illustrate the importance of juvenile growth periods and how early‐in‐life declines in growth may not be offset by above average growth as adults and help further our understanding of how environmental conditions influence growth.

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