Rising sea level to take big bite from Hawaii beaches

Study projects increasing rate of coastal erosion

The Hawaiian Islands via NASA Earth Observatory.

Staff Report

FRISCO — As sea level rises, Hawaii’s beaches are on track to shrink by 20 to 40 feet during the next few decades, scientists announced in a new study.

“When we modeled future shoreline change with the increased rates of sea level rise projected under the IPCC’s “business as usual” scenario, we found that increased SLR causes an average 16 – 20 feet of additional shoreline retreat by 2050,” said lead author Tiffany Anderson, a post-doctoral researcher at the UHM School of Ocean and Earth Science and Technology.

Mapping historical shoreline change provides useful data for assessing exposure to future erosion hazards, even if the rate of sea level rise changes in the future. The predicted increase in erosion will threaten thousands of homes, many miles of roadway and other assets in Hawai’i. Globally the asset exposure to erosion is enormous.

Unless the rate of sea level rise slows, Hawaii’s beaches could retreat another 60 feet by 2100, Anderson said, explaining that the research team’s modeling projected a steep increase in the rate of shoreline erosion.

“Further, our results indicate that approximately 92 percent and 96 percent of the shorelines will be retreating by 2050 and 2100, respectively, except at Kailua, Oahu which is projected to begin retreating by mid-century.”

The research was done by scientists with  the University of Hawaii – Manoa and the Hawai’i Department of Land and Natural Resources and the findings were published this week in Natural Hazards.

The model accounts for accretion of sand onto beaches and long-term sediment processes in making projections of future shoreline position. As part of ongoing research, the resulting erosion hazard zones are overlain on aerial photos and other geographic layers in a geographic information system to provide a tool for identifying resources, infrastructure, and property exposed to future coastal erosion.

“This study demonstrates a methodology that can be used by many shoreline communities to assess their exposure to coastal erosion resulting from the climate crisis,” said Chip Fletcher, Associate Dean at the UHM School of Ocean and Earth Science and Technology and co-author on the paper.

“With these new results government agencies can begin to develop adaptation strategies, including new policies, for safely developing the shoreline,” said Anderson.

To further improve the estimates of climate impacts, the next step for the team of researchers will be to combine the new model with assessments of increased flooding by waves.


2 thoughts on “Rising sea level to take big bite from Hawaii beaches

  1. The tide gauges of Hawaii tell us the acceleration in the rate of sea level rise at:

    Hilo since 1927 is a minus -0.04 mm/yr²
    Kawaihae since 1992 is 0.9 mm/yr²
    Kahului Harbor since 1951 is a minus -0.02 mm/yr²
    Honolulu since 1905 is a minus -0.014 mm/yr²
    Mokuoloe Island since 1958 is a minus -0.003 mm/yr²
    Port Allen since 1990 is a minus -0.5 mm/yr² (Only five years)
    Nawiliwili Bay since 1955 is a minus -0.03 mm/yr²

    Six of the seven tide gauges in the islands say the rate of sea level rise is negative and has slowed down over the years.

    Data is from the Permanent Service for Mean Sea Level. Anyone can Google the PSMSL and download the data into an Excel spreadsheet and verify these numbers.

    Steve Case
    Milwaukee, WI

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