Inundation Exposure Assessment for Majuro Atoll, Republic of the Marshall Islands

The Majuro Atoll inundation grids are useful for characterizing and quantifying inundation exposure and related vulnerability of the atoll's low-relief lands and their population, buildings, infrastructure, and natural resources. The grids represent various scenarios of inundation and different approaches to mapping the inundation levels. The inundation scenarios include static inundation (without wave action) at 15 inches (1.25 ft, or 0.381 m), 30 inches (2.5 ft, or 0.762 m), and 45 inches (3.75 ft, or 1.143 m) above mean higher high water. The areas subject to these inundation levels are mapped separately for marine inundation (areas with a direct overland hydrologic connection to the ocean) and disconnected low-lying areas (with no direct overland flowpath connection to the ocean). These areas are mapped with three different approaches: deterministic, modified deterministic, and probabilistic, the last two being the methods that incorporate consideration of vertical uncertainty, so results can be expressed at a specific confidence level or probability. The grids from the modified deterministic approach include results (minimum and maximum projected areas) presented at the 68% and 95% confidence levels. The grids from the probabilistic approach include results presented at 68% and 95% probability of inundation at the specified increased water levels. Additionally, an example episodic inundation event, in this case projected high wave run-up, has also been mapped using deterministic and probabilistic approaches. Collectively, all the grids help demonstrate the variable mapping of projected inundation zones across the three different methods, and the enhanced information from accounting for vertical uncertainty.