Coastal exposure of the Hawaiian Islands using GIS-based index modeling

Abstract

High energy wave environments intensify the impacts of sea level rise and create threats to island communities, which requires measures to prevent the loss of lives and assets. There is a need to identify hazard-prone sites in order to mitigate and reduce threats. In this study, the overall coastal exposure of Hawai‘i's shoreline, accounting for topography, bathymetry, wave, surge, and sea level rise is estimated along with interactions with natural habitats, coastal defense structures, and human activities. We quantify coastal exposure using the Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST) model, which provides relative comparisons between shoreline segments to identify the most hazardous locations in the state. The study includes estimates of the probability of erosion and calculates exposure index metrics for at-risk areas. Although the average exposure index of the islands at the low to medium vulnerability level, an alarming 34% of the state has moderate to high vulnerability. Geomorphology and wave exposure cause the high levels of risk. Maui, O‘ahu, and Kaua‘i are the top three most vulnerable islands. While geomorphology is most important in influencing vulnerability on O‘ahu, and Kaua‘i, sea level rise, and surge potential are the most influential factors on Maui and Kaho‘olawe, respectively. Although high wave energy affects all the Hawaiian Islands, Lana‘i and Kaua‘i are especially influenced by wave exposure while O‘ahu has the most eroded shorelines. Natural habitats serve as barriers to the adverse effects of exposure and reduce vulnerabilities. The observed probability distribution of the exposure and erosion indices for islands is also provided. By understanding which shorelines are most sensitive and the dominant factors affecting their vulnerability, policymakers can promote public awareness and support planning, design, and implementation of adaptation strategies.