Projected flood water depths on Roi-Namur, Kwajalein Atoll, Republic of the Marshall Islands

Projected future wave-driven flooding depths on Roi-Namur Island on Kwajalein Atoll in the Republic of the Marshall Islands for a range of climate-change scenarios.
This study utilized field data to calibrate oceanographic and hydrogeologic models, which were then used with climate-change and sea-level rise projections to explore the effects of sea-level rise and wave-driven flooding on atoll islands and their freshwater resources. The overall objective of this effort, due to the large uncertainty in future emissions (and thus climate change scenarios) that is largely irreducible, was to reduce risk and increase island resiliency by providing model simulations across a range of plausible future conditions. This effort focuses on Roi-Namur Island on Kwajalein Atoll in the Republic of the Marshall Islands (RMI). RMI is home to more than 1,100 low-lying islands on 29 atolls, yet the approach and findings presented in this study can serve as a proxy for atolls around the world, most of which have a similar morphology and structure, including on average, even lower land elevations, and are the home for numerous island nations and hundreds of thousands of people.
The primary goal of this investigation was to determine the influence of climate change and sea-level rise on wave-driven flooding and the resulting impacts to infrastructure and freshwater resources on atoll islands. First, we mapped the morphology and benthic habitats of the atoll to determine the influence of spatially-varying bathymetric structure and hydrodynamic roughness on wave propagation over the coral reefs that make up the atoll. Second, we analyzed historic meteorologic and oceanographic data to provide historical context for the limited in-situ data and comparison to previous seawater overwash and flooding events. These data were then used to calibrate and validate physics-based, dynamically-downscaled numerical models to project future atmospheric and oceanic forcing for a range of climate-change scenarios. Third, we made in-situ observations to better understand how changes in meteorologic and oceanographic forcing controlled wave-driven water levels, seawater flooding of the island, and the resulting hydrogeologic response. We then used those data to calibrate and validate a physics-based, numerical hydrodynamic model of the island. The hydrodynamic model was used to forecast future wave-driven island overwash and seawater flooding for a range of climate-change and SLR scenarios. The data provided here are the seawater flooding depths for three Intergovernmental Panel on Climate Change (IPCC) AR5 climate-change scenarios: Representative Concentration Pathways (RCP)4.5 and RCP8.5, representing medium and high greenhouse concentration trajectory scenarios, respectively, and RCP8.5 plus icesheet collapse (RCP8.5i). The climate-change scenarios were incorporated into the model by increasing mean sea level based on the future sea-level rise and wave projections. The modeled time frame ranged from 2035 to 2105 at 10-yr time steps.
These data accompany the following publication: Storlazzi, C.D., Gingerich, S.B., van Dongeren, A., Cheriton, O.M., Swarzenski, P.W., Quataert, E., Voss, C.I., Field D.W., Annamalai, H., Piniak G.A., McCall, R., 2018, Most atolls will be uninhabitable by the mid-21st century due to sea-level rise exacerbating wave-driven flooding, Science Advances, https://doi.org/10.1126/sciadv.aap9741.