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NOAA says sunny-day flooding accelerates with sea level rise

National Oceanic and Atmospheric Administration
Streets in Charleston, S.C., flood frequently on storm-free days, including seven times over the past year above 1.75 feet.

Federal scientists say high-tide flooding is becoming more common on the East and Gulf coasts and the risk is accelerating as the ocean rises due to climate change.

High-tide or sunny day flooding now happens twice as often as it did in 2000, according to the National Oceanic and Atmospheric Administration, or NOAA. The agency defines it as 1¾ to 2 feet above daily average tides and water levels that can flood coastal downtowns and neighborhoods.

NOAA said in a new report out Tuesday that coastal communities could see three to seven days of high-tide flooding over the one year period between May 2021 and April 2022.

And with sea levels expected to rise another foot by 2050, that could grow to 45 to 70 days per year, said NOAA oceanographer William Sweet.

That suggests "high-tide flood days may become the new high tide in many locations," Sweet told reporters Tuesday.

Sweet said flooding brings risks and NOAA has produced these reports to help coastal communities prepare.

"This is the information needed to protect life, property, the economy and our environment for future generations," Sweet said. "For the first time in human history, the infrastructure we build must be designed and constructed with future conditions in mind. These data can help communities plan where to put their buildings and how to build them to keep people safe."

Sweet and his colleagues studied data from 97 tide gauges along the U.S. coast, including the Carolinas. They found that about 80% of the East Coast and Gulf Coast are seeing an acceleration in the number of annual high-tide flood days.

"The line is no longer a straight line. It's an upward curving line," Sweet said. "And that means that impact's sort of growing in leaps and bounds."

He said the impacts will go from occasional to chronic "rather quickly," such as "water coming out of stormwater drains when it's sunny outside."

Sweet said that higher tides are already affected by the weather patterns known as La Nina and El Nino. But those Pacific Ocean phenomena are also amplified by climate change, according to NOAA.

In the Carolinas, the study reported a mix of increases and decreases in high-tide flooding over the past year, and elevated projections for the current 12 months through April 2023. Some communities set records last year, including Springmaid Pier, near Myrtle Beach, S.C., which tied its 2021 record with 11 high tide flooding days over the past year. Other examples in the report:

  • Oregon Inlet Marina - High-tide flood days in 2000, 1; high-tide flood days in 2021, 5; next 12 months, 3 to 7; 2050, 110 to 155 days annually.
  • Beaufort, NC - High-tide flood days in 2000, none; high-tide flood days in 2021, 8; next 12 months, 3 to 5; 2050, 70 to 100 days annually. 
  • Wilmington - High-tide flood days in 2000, 1; high-tide flood days in 2021, 2; next 12 months, 2 to 6; 2050, 40 to 65 days annually. 
  • Springmaid Pier (near Myrtle Beach) - High-tide flood days in 2000, 2; high-tide flood days in 2021, 11; next 12 months, 5 to 10; 2050, 55 to 75 days annually. 
  • Charleston - High-tide flood days in 2000, 2; high-tide flood days in 2021, 7; next 12 months, 5 to 9; 2050, 70 to 90 days annually. 

NOTE: In this report, NOAA only counted the days where flooding exceeded the 1.75 to 2 foot level. In some areas, high-tide flooding occurs at lower levels more regularly.
You can see a map and this year's projections at https://tidesandcurrents.noaa.gov/HighTideFlooding_AnnualOutlook.html.

Corrected: August 3, 2022 at 9:58 AM EDT
This story has been updated to correct the full name of the National Oceanic and Atmospheric Administration.
David Boraks is a veteran journalist who covers climate change for WFAE. See more at www.wfae.org/climate-news. He also has covered housing and homelessness, energy and the environment, transportation and business.