Study: We’ve been measuring the impacts of sea level rise in Hawaii all wrong

It’s worse than previously thought.
Previous studies underestimate the amount of land in the island vulnerable to rising sea...
Previous studies underestimate the amount of land in the island vulnerable to rising sea levels, new research concludes.(UH Sea Grant)
Updated: Oct. 11, 2018 at 12:41 PM HST
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HONOLULU (HawaiiNewsNow) - The land area in Hawaii vulnerable to sea level rise could be double previous estimates, a newly-published study concludes.

A team of University of Hawaii and state researchers partnered to produce the new estimates, based on improved understandings of how rising sea levels would affect Hawaii's geography.

Tiffany Anderson, a faculty member at UH-Manoa’s School of Ocean and Earth Science and Technology and lead researcher for the study, said previous estimates of the impacts of sea level rise were based on the so-called “bathtub model.” In other words, they imagined water simply creeping farther inland as sea levels rise.

That model offers an adequate look at how rising sea levels would affect low-lying, flood-prone areas.

But the “bathtub approach,” the study concludes, ignores a whopping 35 to 54 percent of the total land area exposed to the other ways that rising sea levels could inundate land, including storm drain back flow, groundwater inundation and rapidly escalating flooding from waves.

The bathtub model also ignores coastal erosion, even though the disappearance of beaches increases the risk of inundation from sea level rise.

The team also found that typical elevations of Hawaii's low-lying coastal plains create thresholds of flood levels, above which rapid increases in flooding occur.

"A large portion of lands at risk of flooding are not in direct proximity to the shoreline," Anderson said.

"Instead, they are low-lying areas where sea level rise causes the groundwater table to rise up to the surface. These areas can be located one to two miles inland from the coastline."

Chip Fletcher, co-author of the study published in the journal Scientific Reports, said it's vital that Hawaii begin to identify all land areas vulnerable to sea level-related hazards -- not the ones just onshore.

“Preparing for these effects will be very costly and take a long time to implement. With these results, stakeholders of all types are now able to establish empirically-based adaptation policies,” Fletcher said.

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