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Resilient Coastal Sites for Hawaii

In this project, we assessed the coastal region of six Hawaiian Islands and estimated the relative resilience or vulnerability of sites containing tidal marsh, tidal flats, and anchialine pools. We identified the sites most likely to continue to support biological diversity and ecological functions under rising sea levels up to 6.5 feet due to their ability to migrate upslope and adapt. 

Hawaiian estuarine wetlands are characterized by swamps, salt- and mudflats, unique anchialine pools, and historic fishponds. As sea levels rise, the Hawaiian Islands are particularly vulnerable and are already experiencing increased rates of inundation and record coastal flooding. The characteristics of some coastal wetlands make them more likely to adapt to sea level rise and remain diverse and productive even as they adjust to climate-induced changes. In this project, we mapped these characteristics and estimated the relative resilience of coastal sites on six Hawaiian Islands. We assessed coastal sites comprised respectively, of tidal marsh, tidal flats, and anchialine pools on the islands of Hawai’i, Kaua’i, Lana’i, Maui, Moloka’i, and O’ahu. For each site, we estimated the amount of migration space available under twenty sea-level rise scenarios. We quantified physical properties of the tidal marsh and tidal flat complexes, and the amount of development potentially blocking migration of these habitats upslope as sea levels increase. While results are available for all twenty SLR scenarios, our final maps are based on the 6.5-foot scenario because this scenario reveals the sites with the greatest long-term potential for adaptive response, and this scenario is a worst-case, but plausible outcome by the end of the century. 

The six Hawaiian Islands in our analysis have approximately 4,000 acres of estuarine wetland sites but could lose up to 87% of these existing estuarine habitats under 6.5 feet of sea level rise. However, our analysis identifies many resilient sites where estuarine habitats could potentially increase in size through landward migration. Some islands and tidal habitats could fare better than others. For example, Hawai’i could have almost three times as much tidal marsh area under a 6.5-foot SLR scenario as it currently has, if marsh migration occurs. The amount of unconsolidated shore on Lana’i and on Maui could stay relatively similar if habitats are able to migrate. In contrast, O’ahu and Moloka’i could lose more than half of their current tidal marsh habitats to inundation, even with marsh migration. These results and others are summarized in the project report and are available for download in the accompanying data package linked below. 

A report describing the methods used to evaluate sites and the results for the six islands we examined.
Downloadable datasets including results for all 20 sea level rise scenarios