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High-tide flooding will rapidly increase along the U.S. coastline

In the mid-2030s, the frequency of coastal flooding will drastically increase across multiple regions in the United States, according to a new study from UH Mānoa. The projections show rapid increases in the number of high-tide flooding (HTF) days, as well as extreme months.

Study lead author Phil Thompson is the director of the UH Sea Level Center and assistant professor of Oceanography in the UH Mānoa School of Ocean and Earth Science and Technology (SOEST).

“We expect the most rapid increases to be along U.S. Pacific and Gulf of Mexico coastlines, which includes Hawaii and other Pacific Islands. This is important, because this is the point at which high-tide flooding transitions from being primarily a local or regional issue and becomes a national issue affecting a majority of our nation’s coastlines,” said Professor Thompson. 

The researchers analyzed tide gauge data from 89 coastal locations around the United States, including 10 locations from Hawaii and the Pacific Islands. To project future occurrences of high-tide flooding, the team developed a new statistical technique that combines changes in tidal range with NOAA sea level rise scenarios for the 21st century.

The study shows that in the coming decades, sea-level rise will exacerbate the issue where it is already a recurring problem, while many more locations will begin to experience recurrent high-tide flooding.

The researchers found that annual cycles in tides can coincide with oceanographic anomalies to produce many high-tide flooding episodes over a short amount of time, leading to extreme months with clustered events.

“Scientists, engineers and decision-makers are accustomed to thinking about rare high-impact events, for example, a 100-year storm, but we demonstrate that it is important to plan for extreme months or seasons during which the number of flooding episodes, rather than the magnitude, is exceptional,” said Professor Thompson.

The experts also determined that natural fluctuations in tidal range, which occur from one decade to the next, are responsible for alternately reducing and exacerbating the impacts of sea level rise.

“Understanding and communicating this phenomenon reduces the possibility of complacency and inaction during periods of reduced impacts and helps us be more prepared for periods when impacts will be heightened,” said Professor Thompson.

“As an island state with much of its infrastructure and economy vulnerable to sea level rise, these results are crucial to understanding how impacts from sea level rise will evolve in coming decades in Hawaii.”

The study is published in the journal Nature Climate Change.

By Chrissy Sexton, Staff Writer

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