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Projections of US high-tide flooding show rapid increases and extreme months

Regional sea-level change between 1992 and 2019, based on data collected from the TOPEX/Poseidon, Jason-1, Jason-2, and Jason-3 satellite altimeters. Blue regions are where sea level has gone down, and orange/red regions are where sea level has gone up. Since 1993, seas around the world have risen an average rate of 3.3 millimeters per year. Credit: NASA's Scientific Visualization Studio.

  • June 21, 2021
  • News

While recurrent flooding during high tides has become familiar to many U.S. communities, including the Atlantic and Gulf coasts, these high-tide flooding (HTF) events are projected to increase rapidly in the mid-2030s, according to a study published in . The team, led by the University of Hawai‘i at Mānoa, included Dr. Gary Mitchum, physical oceanography Professor and Associate Dean at the ±«Óătv College of Marine Science.

The team analyzed tide gauge data from 89 coastal locations around the US, including St. Petersburg, and developed a novel statistical technique that combined natural fluctuations in tidal ranges with NOAA sea level rise scenarios to produce the projections of high-tide flooding. The analyses show “tipping points” when the frequency of HTF events increase abruptly.

For example, the analyses indicate a tipping point for St. Petersburg may occur around 2033. The St. Petersburg area may see less than ten HTF events every year between 2023-2033, but that projection increases to nearly 70 per year in the following decade (2033-2043).

“Events we used to call extreme are likely to become routine, and the projected number of events is cause for concern,” said Mitchum. “We have to keep in mind that flooding events are highly localized in nature, but these estimates do provide a blueprint that we hope helps guide coastal planning efforts.”

The impact of seemingly minor occurrences of HTF adds up and can exceed the impact of rare extremes over time. These impacts are subtle—for example, the loss of revenue due to recurrent road and business closures—compared with the physical damage of property and infrastructure associated with extreme storm-driven events.

The most rapid increases are along the Gulf of Mexico and the US Pacific, which includes HawaiÊ»i 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 lead author Phil Thompson, director of the UH Sea Level Center and assistant professor