PREDICTING CLIMATE CHANGE DRIVEN EROSION ON THE ARCTIC COAST

Background: Post WW-II the US Air Force (USAF) built a number of early warning radar facilities along the coast of the Arctic Ocean at geologically stable sites. The Arctic warms at up to 5 times the rate of tropical areas as melting snow and ice results in 80-90% increase in retained solar energy, a shallower Arctic atmosphere is easier to warm, greater proportion of land vs. marine environment etc. This has raised Arctic temperatures that have resulted in a 75% reduction of Arctic Ocean ice volume since 1979 which in turn has destabilized the coastline leading to unprecedented rates of erosion. In the early 2000’s erosion began threatening landfills associated with radar sites. Over the next dozen years over $60 million was spent moving these threatened landfills. Now some radar facilities themselves are being threatened ($48 million sea wall planned for one site). In 2009 the US Army Corps of Engineers (COE) made the first effort at predicting coastal erosion in northern and western Alaska. At one site the coast eroded an alarming 480 feet in 8 years reaching a point in 2014 that was predicted for 2040 in the COE model! Clearly better understanding of erosion mechanisms and more accurate models were needed. Methods: To find the best existing coastal erosion model to make more accurate predictions, thirteen models were evaluated by assigning each a score of 0-3 in seven factors. These factors were: Arctic specific, data easily obtained, model is open source, ease of setup, account for climate change, adjustable for different scenarios and reliability. A sensitivity study with an existing Arctic coastal erosion model developed for Drew Point Alaska, found that coastal erosion rates were particularly sensitive to nearshore water temperature, the elevation of the beach before the coastal bluff, and the spatial and temporal extent of open water. Thus, in seeking appropriate coastal erosion models, we sought models that took account of these important variables. Results: The factors leading to unprecedented and accelerating erosion rates along the Arctic Coast include: 1. Shorefast ice no longer forming early enough to protect shoreline from fall storms. 2. Without significant offshore ice increased fetch results in larger waves. 3. Increasing air and water temperatures provided energy for more speedy movement of sediments. 4. As it melts permafrost dominated shorelines lose their boulder-like qualities. 5. At many sites “block erosion” was identified as a particularly rapid mechanism (large blocks of permafrost bluffs are undercut by large warm waves causing multi-ton blocks to break off into the ocean and wash away). After scoring each of the thirteen existing erosion models the winner with 15 points was the “Process-Based Semi-Empirical Model” developed by University of Alaska Anchorage and the US Geologic Survey. Conclusion: The USAF is considering a project to collect the field data necessary to run the Process-Based Semi-Empirical Model at selected sites and evaluating it for wider application to USAF Arctic facilities.