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Boston could see up to 18 days of high-tide flooding next year, NOAA says

Even on sunny days, seawater creeps onto some streets in Boston.Adam Glanzman/The Washington Post

Boston this year could have more than three times the number of days with high-tide flooding than the city experienced in 2000, according to a new report by federal scientists.

The report, released this week by the National Oceanic and Atmospheric Administration, projects the city could have between 11 and 18 days of high-tide flooding by the end of the year. High-tide flooding, also known as sunny-day flooding, is when coastal waters rise 1.8 feet or more above the typical daily high tide.

“High tide flooding is becoming more common and damaging in many parts of the U.S.,” said Rick Spinrad, NOAA’s administrator, in a statement accompanying the report.

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The increase in high-tide flooding is mainly the result of rising sea levels, which have increased by about a foot over the past century. As rising temperatures as a result of climate change warm the oceans and melt glaciers around the world, sea levels are expected to rise at an accelerating rate over the coming years.

Seas are now rising on average about an inch every eight years, and the number of days that coastal areas are likely to experience high-tide flooding is projected to increase sharply in the coming years. NOAA projects that sea levels could rise between 2 feet and 7 feet by 2100 and as high as 12 feet by 2150.

The report projects that Boston could have between 50 and 70 days of high-tide flooding every year in 2050, which is down from as many as 95 days of such flooding that NOAA projected for 2050 in last year’s report.

“The updated 2050 numbers are based upon the updated science,” said William Sweet, a NOAA oceanographer and one of the authors of the report.

The city’s record for such flooding was set in 2017, when high tides inundated parts of Boston during 22 days, more than any other community on the East Coast.

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In addition to rising sea levels, high-tide flooding can be affected by changes in prevailing winds, shifts in ocean currents, and by the phase of the moon.

In the next few years, high tides in Boston may be lower than the highest projections, as the region is at the low end of an 18.6-year tidal cycle, Sweet said. In the mid 2030s, when the moon’s orbit changes slightly and the tidal cycle peaks, high-tide flooding will be that much greater.

Flooding may also be tempered by the impact of a complex weather phenomenon known as La Niña, which occurs when strong winds blow warm water away from South America and across the Pacific Ocean. The phenomenon can affect weather across the planet.

Last year, NOAA projected that Boston would have as many as 18 days of high-tide flooding; the city had just seven days of such floods.

Still, the rate of flooding in Boston has been accelerating. Between 2010 and 2020, Boston experienced 152 days of high-tide flooding — more than in the previous 45 years — and more than triple the national average, according to NOAA data. During the same period, NOAA’s tide gauges around the country registered an average of 49 days of high-tide flooding.

Boston has actually registered more high-tide flooding than any other city in the country, with a total of 371 days since NOAA began keeping records in 1920.

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Still, high-tide flooding is a growing problem that affects coastal communities everywhere.

Last year, three coastal communities in the United States experienced record high-tide flooding, according to the report. NOAA officials said they expect more records in the coming years.

Reedy Point, Del., experienced six high-tide flooding days, while Kwajalein Island in the Marshall Islands had four days and Springmaid Pier, S.C., near Myrtle Beach, tied its 2021 record with 11 high-tide flooding days.

The report projects that high-tide flooding between May 2022 and April 2023 will occur on average between three and seven days, the same as the previous year. That’s an increase from the two to six days expected between 2019 and 2020.

By 2050, high-tide flooding is expected to occur an average of between 45 and 70 days per year in coastal communities across the country, according to the report.

NOAA officials said coastal flood warnings for “significant potential risks to life and property” will become more common.

“The East and Gulf coasts already experience twice as many days of high tide flooding compared to the year 2000, flooding shorelines, streets and basements, and damaging critical infrastructure,” said Nicole LeBoeuf, director of NOAA’s National Ocean Service.


David Abel can be reached at david.abel@globe.com. Follow him on Twitter @davabel.