SANTA CRUZ, Calif. — A new study shows that the combined effect of storm-induced wave-driven flooding and sea level rise on island atolls may be more severe and happen sooner than previous estimates of inundation predicted by passive “bathtub” modeling for low-lying atoll islands, and especially at higher sea levels forecasted for the future due to climate change. More than half a million people live on atolls throughout the Pacific and Indian Oceans, and although the modeling was based on the Northwestern Hawaiian Islands, the results from the study apply to almost all atolls.

U.S. Geological Survey scientists and their colleagues at the Deltares Institute in the Netherlands, and the Hawaii Cooperative Studies Unit at University of Hawaii, Hilo report that numerical modeling reveals waves will synergistically interact with sea level rise, causing twice as much land forecast to be flooded for a given future sea level than currently predicted by models that do not take wave-driven water levels into account.

Observations show global sea level is rising due to climate change, with the highest rates in the tropical Pacific Ocean where many of the world’s low-lying atolls are located. Sea level rise is particularly critical for low-lying coral reef-lined atoll islands; these islands have limited land and water available for human habitation, limited food sources and ecosystems that are vulnerable to inundation from sea level rise. Sea level rise will result in larger waves and higher wave-driven water levels along atoll islands’ shorelines than at present.

“Many atoll islands will be flooded annually, contaminating the limited freshwater resources with saltwater, and likely forcing inhabitants to abandon their islands in decades, not centuries, as previously thought,” said USGS geologist and lead author of the study, Curt Storlazzi.

The study explored the combined effect of storm-induced wave-driven flooding and sea level rise on atoll islands within the Northwestern Hawaiian Islands, including Laysan and Midway Islands, which are home to many threatened and endangered endemic species. The same modeling approach is applicable to most populated atolls around the world.

The study, “Many Atolls May Be Uninhabitable Within Decades Due to Climate Change,” was recently published in Nature’s Scientific Reports journal, and is available online.

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