Inundation Exposure Assessment for Majuro Atoll, Republic of the Marshall Islands
Dates
Publication Date
2019-07-02
Time Period
2016
Citation
Gesch, D.B., Danielson, J.J., and Palaseanu-Lovejoy, M., 2019, Inundation Exposure Assessment for Majuro Atoll, Republic of the Marshall Islands: U.S. Geological Survey data release, https://doi.org/10.5066/P9K1GD9W.
Summary
Low-lying island environments, such as the Majuro Atoll in the Republic of the Marshall Islands, are particularly vulnerable to inundation (coastal flooding) whether the increased water levels are from episodic events (storm surge, wave run-up, king tides) or from chronic conditions (long term sea-level rise). Land elevation is the primary geophysical variable that determines exposure to inundation in coastal settings. Accordingly, coastal elevation data are a critical input for assessments of inundation exposure and vulnerability. Previous research has demonstrated that the quality of data used for elevation-based assessments must be well understood and applied to properly model potential impacts. The vertical uncertainty of the input [...]
Summary
Low-lying island environments, such as the Majuro Atoll in the Republic of the Marshall Islands, are particularly vulnerable to inundation (coastal flooding) whether the increased water levels are from episodic events (storm surge, wave run-up, king tides) or from chronic conditions (long term sea-level rise). Land elevation is the primary geophysical variable that determines exposure to inundation in coastal settings. Accordingly, coastal elevation data are a critical input for assessments of inundation exposure and vulnerability. Previous research has demonstrated that the quality of data used for elevation-based assessments must be well understood and applied to properly model potential impacts. The vertical uncertainty of the input elevation data controls to a large extent the increments of water level increase and planning horizons that can be effectively used in an assessment. Recent high-resolution elevation data along the coast exhibit high vertical accuracy, and thus have become indispensable for assessments, whether a simple inundation model is used, or a more sophisticated process-based or probabilistic model is employed. When properly characterized, the vertical accuracy of the high-resolution, high-accuracy elevation data can be used to generate maps and report assessment results with the uncertainty stated in terms of a specific confidence level. This data release includes the results of a quantitative assessment of inundation exposure for Majuro Atoll, including rigorous accounting for the cumulative vertical uncertainty in the input geospatial data (elevation model) and data processing (datum transformations). The project employed a recently produced and validated high-resolution, high-accuracy topobathymetric digital elevation model (TBDEM) covering Majuro Atoll. Areas subject to marine inundation (direct hydrologic connection to the ocean) and low-lying land (no direct hydrologic flowpath to the ocean) were mapped and characterized for different inundation levels.
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Inundation_Exposure_FGDC_Metadata_Final_Clean.xml Original FGDC Metadata
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Inundation_Exposure_Raster_Layers.zip
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Purpose
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.
