Inundation Exposure Assessment for Select Islands in the Republic of the Marshall Islands

As a low-lying island nation, the Republic of the Marshall Islands (RMI) is at the forefront of exposure to climate change impacts, including, primarily, inundation (coastal flooding). Increased water levels can stem 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, accurate 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, such as the digital elevation models (DEMs) used here, exhibit high vertical accuracy, and thus have become indispensable for inundation exposure assessments. 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, which is the approach employed here. This data release includes the results of a quantitative assessment of inundation exposure for five selected sites in RMI (Aur Island and Tobal Island in Aur Atoll, Ebon Island in Ebon Atoll, Likiep Island in Likiep Atoll, and Mejit Island), including rigorous accounting for the vertical uncertainty in the input elevation model data. 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.

作为低洼岛国，马绍尔群岛共和国（Republic of the Marshall Islands, RMI）是受气候变化影响最前沿的国家之一，其首要面临的威胁为淹没（海岸洪水）。水位上升可源于偶发事件（风暴潮、海浪上涌、天文大潮），也可由长期海平面上升这类慢性状况引发。陆地海拔是决定海岸区域淹没暴露风险的核心地球物理变量，因此精准的海岸海拔数据是淹没暴露与脆弱性评估的关键输入项。既往研究证实，开展基于海拔的评估时，必须充分明晰所用数据的质量，并将其应用于潜在影响的精准建模。输入海拔数据的垂直不确定性，在很大程度上控制着评估中可有效采用的水位上升增量与规划时限。近期发布的海岸高分辨率海拔数据，如本次研究所使用的数字高程模型（digital elevation models, DEMs），具备极高的垂直精度，现已成为淹没暴露评估不可或缺的工具。若对其垂直精度进行恰当表征，则可基于特定置信水平明确不确定性，生成相关地图并报告评估结果，本次研究即采用了这一方法。本次数据发布包含了马绍尔群岛共和国5个选定站点（奥罗环礁的奥罗岛与托巴尔岛、埃本环礁的埃本岛、利基普环礁的利基普岛，以及梅吉特岛）的淹没暴露定量评估结果，其中严格核算了输入高程模型数据的垂直不确定性。研究对受海洋淹没（与海洋存在直接水文连通）的区域以及低洼陆地（无直接水文入海路径的区域）进行了制图，并针对不同淹没等级开展了特征分析。