Meteorologic and oceanographic forcing were used to model
dynamic wave-driven water levels and inundation at Midway Atoll
and Laysan Island in the Northwestern Hawaiian Islands for five
different sea-level rise (SLR) scenarios and compare the
results to pa**ive inundation modeling of the same islands.
Key findings from these modeling efforts and subsequent an*lyses
include:
1. The modeled dynamic wave set-up, run-up, and total
wave-driven water levels for all SLR scenarios were greater for
North Pacific winter swell conditions than for the summer
tradewind waves. At higher SLR scenarios, less wave breaking
on the reef crests resulted in larger waves and longer
wavelengths on the islands' shorelines. Although wave-driven
set-up decreased at higher SLR scenarios, the increases in
wave height and wavelength at higher SLR scenarios resulted in
greater wave-driven run-up and thus higher total water levels
along the islands' shorelines.
2. Across all SLR scenarios (+0.00, + 0.50, + 1.00, + 1.50,
and + 2.00 m), the extent of inundation predicted under the
pa**ive modeling approach covered less area than the inundation
extent forecasted by the dynamic modeling approach. For the
higher SLR scenarios, the dynamic inundation patterns start to
diverge considerably from pa**ive inundation patterns, as
wavedriven water levels began to exceed existing coastal berms
and extend considerable distances inland over low-lying areas.
3. The changes in land cover cla**es follow similar patterns
to the overall patterns of inundation, with all islands
losing more of the existing land cover at lower values of
future SLR under the dynamic modeling than suggested by the
pa**ive modeling. Overall, the dynamic modeling predicts, on
average, almost one-half to a full order of magnitude
greater inundation of the different land cover cla**es for a
given SLR scenario than is predicted by the pa**ive modeling.
4. Assuming that sea level will continue to rise over the next
century, the dynamic model results that include wave-driven
processes presented here suggest that a given percentage of the
atoll islands and their a**ociated habitats will be
episodically inundated at lower values of SLR and thus sooner
in the future than predicted by the pa**ive “bathtub” models.
5. Observations and the modeling results presented here suggest
that cla**ic atolls with islands on the shallow atoll rim are
more susceptible to the combined effects of sea-level rise and
wave-driven inundation than atolls characterized by a deep
atoll rim.
The dynamics of SLR and wave-driven inundation on low-lying
atoll islands are complex in nature. The results presented
here can provide information to identify the areas of
vulnerability specific to each island. These models help
display the relative impacts expected to occur, given the
current knowledge of these complex systems, and may improve
understanding of potential effects on natural resources
needed for planning management of the atoll islands in
the face of changing climate and sea level.