Frequency, timing, extent, and size of winter thaw-refreeze events in Alaska 2001–2008 detected by remotely sensed microwave backscatter data

Abstract

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.