Frequency, timing, extent, and size of winter thaw-refreeze events in Alaska 2001–2008 detected by remotely sensed microwave backscatter data
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Creation of ice layers in snow due to thaw-refreeze events can lock away winter forage, preventing access by large mammals and causing population declines. Data are limited, however, on the frequency, timing, extent, and size of thaw-refreeze events in northern latitudes given the area’s remoteness and paucity of weather stations. We used a remote sensing approach to detect thaw-refreeze events in Alaska during winter between 2001 and 2008. We also compared these results to a regional climate reanalysis dataset that identified rain events (freezing and non-freezing rain). All areas of the state, except high elevation sites, had ≥1 thaw-refreeze event during the study period. Southwestern Alaska had the highest frequency of thaw-refreeze events with an average of >4 events each winter, whereas northern Alaska had the lowest frequency with an average of <2 events. We observed substantial inter-annual variation in the distribution and frequency of thaw-refreeze events. For most of the state, thaw-refreeze occurred at similar rates each winter month, except in northern Alaska where thaw-refreeze events were most frequent in early and later winter. The median extent of individual thaw-refreeze events was 469 km2, however, events in the interior of the state tended to be larger. Remotely sensed thaw-refreeze detections generally had low correspondence with observations from the climate reanalysis dataset. Our results support the use of remotely sensed data to identify thaw-refreeze events.
KeywordsAlaska Freezing rain Ice QuikSCAT Rain-on-snow Remote sensing ROS Scatterometer Snow characteristics
This study was funded by the Western Alaska Landscape Conservation Cooperative. We thank S. McAffee, M. Cornelison, J. Dau, and B. Griffith for providing valuable comments on an earlier version of this manuscript.
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