Title: Vulnerability of a subarctic barrier spit to global warming induced changes in
storm surge and wave runup: Shaktoolik, Alaska
Authors: Ohman, K.A., Michael Baker International; Erikson, L.H., United States
Geological Survey
Primary Author:
Karin Ohman, Coastal Scientist
Michael Baker International
3601 Eisenhower Ave.
Alexandria, VA 22304
703-317-3059
Karin.Ohman@mbakerintl.com
Presenter Bio:
Karin is a Coastal Scientist at Michael Baker Jr., Inc. She holds a M.S. in Earth
Science from the University of California, Santa Cruz and a B.S. in Geology from The
College of William & Mary. As a graduate student, Karin worked at the USGS Pacific
Coastal and Marine Science Center and after finishing her degree she continued working
there full-time for a year. At USGS, she supported coastal modeling projects in Alaska
and California. Karin started working for Michael Baker Jr., Inc. in November 2013. At
Baker, she has engaged in a sea level rise assessment for New York City area airports and
FEMA related work in California, Georgia and Florida.
Abstract:
The native Inupiaq community of Shaktoolik, in northwestern Alaska, is located
on a low-lying barrier spit located on Norton Sound. The inhabited portion of the spit is
7.1 m above MLLW at its highest and only ~200 m across. The community is vulnerable
to marine flooding on both the open ocean and lagoon sides of the spit during storms.
Storm events in this region typically occur during the fall and winter months, often when
the coastline is protected from flooding and erosion by shorefast ice. High latitudes are
experiencing the greatest increases in temperature due to global warming and the reduced
duration and extent of sea ice is affecting Alaskan coastal communities. Continued
reduction of sea ice protecting the coastline from exposure during large storm events may
result in the need to relocate many Native Alaskan coastal communities.
The goal of this study was to quantify changes in storm surge and wave runup
during ice-free months for the mid to late 21st century. An analytical approach was
developed to quantify storm surge in Alaskan coastal communities with historical
meteorological data from the North American Regional Reanalysis. This analytical
model was used to calculate projected storm surge inundation levels in Shaktoolik for the
mid and late 21st century for both a moderate and high greenhouse gas emissions scenario
(RCP 4.5 and RCP 8.5 respectively), with meteorological output from the MIROC5
global climate model as part of the Coupled Model Intercomparison Project Phase 5
(CMIP5). Additionally, projected wave runup heights during storm events were
calculated numerically using WAVEWATCH III to calculate wave height and period
from the projected MIROC5 meteorological data and SBEACH to model the maximum
runup heights along the Shaktoolik shoreline.
Total storm water levels (storm surge plus wave runup height) were calculated for
602 projected storm events in the Bering Sea and used to find the return periods of
inundation for each emissions scenario. When compared to historical total storm water
levels, the results show that the moderate emissions scenario has a higher storm
frequency and greatest change in return periods of inundation for storm surge. The high
emissions scenario produces lower storm frequency than the moderate emissions scenario
and the return periods of inundation for storm surge are similar to the historical values.
When wave setup and runup are included in the total inundation levels for the
moderate emissions scenario the results are similar to historical values, and when wave
setup and runup are included in the high emissions scenario the total inundation levels are
lower than historical values. The 100-yr flood level is +11.4 m above MLLW for the
moderate emissions scenario and +13.5 m for the high emissions scenario, compared to
+11.2 m historically. All three of these inundation levels overtop the highest ground
elevation in the community.