U.S. Geological Survey - (Conclusion) Forecasting the Impact of Storm Waves and SeaLevel Rise on Midway Atoll and Laysan Island within the Papahānaumokuākea Marine National Monument—A Comparison of Pa**ive Versus Dynamic Inu lyrics

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.