Abstract
Abstract. Using thresholds of physical climate variables developed from community observations, together with two large-scale datasets, we have produced local indices directly relevant to the impacts of a reduced sea ice cover on Alaska coastal communities. The indices include the number of false freeze-ups defined by transient exceedances of ice concentration prior to a corresponding exceedance that persists, false break-ups, timing of freeze-up and break-up, length of the open water duration, number of days when the winds preclude hunting via boat (wind speed threshold exceedances), the number of wind events conducive to geomorphological work or damage to infrastructure from ocean waves, and the number of these wind events with on- and along-shore components promoting water setup along the coastline. We demonstrate how community observations can inform use of large-scale datasets to derive these locally relevant indices. The two primary large-scale datasets are the Historical Sea Ice Atlas for Alaska and the atmospheric output from a regional climate model used to downscale the ERA-Interim atmospheric reanalysis. We illustrate the variability and trends of these indices by application to the rural Alaska communities of Kotzebue, Shishmaref, and Utqiaġvik (previously Barrow), although the same procedure and metrics can be applied to other coastal communities. Over the 1979–2014 time period, there has been a marked increase in the number of combined false freeze-ups and false break-ups as well as the number of days too windy for hunting via boat for all three communities, especially Utqiaġvik. At Utqiaġvik, there has been an approximate tripling of the number of wind events conducive to coastline erosion from 1979 to 2014. We have also found a delay in freeze-up and earlier break-up, leading to a lengthened open water period for all of the communities examined.
Highlights
1.1 Identification of metrics useful for describing climate change-related impacts on Arctic coastal communitiesCommunity engagement and feedback are useful to identify the social relevance of climate system variables commonly used by scientists, as covered extensively by Krupnik and Jolly (2002)
While the definition of freeze-up and break-up timing can vary based on data source (Johnson and Eicken, 2016), it is useful to evaluate these metrics in a way that can be applied across communities, as done in this study
We describe the data and methods, which are separated into subsections describing the Historical Sea Ice Atlas (HSIA) and downscaled ERA-Interim datasets, sources of community observations, the rationale for the selection of the study areas, and descriptions of the locally relevant metrics of the changing sea ice conditions in these communities
Summary
1.1 Identification of metrics useful for describing climate change-related impacts on Arctic coastal communities. For indigenous Arctic coastal communities, the timing of local freeze-up and break-up is among the most important characteristics of sea ice (Berkes and Jolly, 2002; Berman and Kofinas, 2004; Laidler et al, 2009). Freeze-up day and break-up are defined by the dates when the ice passes a sea ice concentration threshold. The timing at which freeze-up and break-up concentration thresholds are passed does not necessarily imply a phase change, but can depend on advection of ice driven by winds or currents. Variations and trends in the number and timing of these events may give an indication of how climate change will impact coastal communities. In this study we present a time series of these indices from 1979 to 2014 (1953–2013 for freeze-up and break-up timing) for three coastal communities in Alaska
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