Boston could see as many as 18 high-tide flooding days in the coming year, the National Oceanic and Atmospheric Administration predicted, while renewing its forecast that the number could grow to as many as 35 by 2030 and 95 by 2050.
In the past meteorological year, which ran through April, Boston saw 11 high-tide flooding days, coming in on the low side of NOAA’s projection for both years of 11 to 18 such days. The past year’s number was still nearly twice as high as what was normal 20 years ago.
The record for such flooding was set in 2017, when high tides inundated parts of the city on 22 days, more than any other community on the East Coast.
The predictions came in a new annual report from NOAA, “2021 State of High Tide Flooding and Annual Outlook.”
NOAA defines high-tide flooding, also known as sunny-day flooding, as water rising about 2 feet above the typical daily high tide. As sea levels rise, damaging floods that used to occur only during storms now happen more regularly, such as during a full moon or with a change in winds or currents. Average sea levels have risen by about a foot over the past century.
Nationally, coastal communities saw twice as many high-tide flooding days last year than they did 20 years ago, NOAA said Wednesday in a statement.
“High-tide flooding is becoming common and damaging in many parts of the US,” William Sweet, an oceanographer for NOAA’s National Ocean Service and lead author of the report, said in the statement. “Many coastal communities are saddled with this problem, so NOAA is working to provide them with the kinds of information needed to anticipate, prepare for, and respond to increasingly frequent high-tide flooding.”
While high-tide flooding days in Boston have declined since the record year, Sweet said it was “just a little bit of a reprieve” and the scientists expected the trend of increases to resume.
“The trends are all going up and they’re all accelerating, even though any given year may be higher or lower. And that just happens to be the case with the Northeast,” Sweet said in a media briefing Wednesday.
Alison Brizius, director of climate and environmental planning for the city of Boston, said in an e-mail, “Climate change is here. And our most vulnerable residents are already bearing the burden. We need to act urgently.” She cited the city’s Climate Ready Boston program and said “we are working to build a more just and resilient city — and ensure all residents can thrive in the face of climate change.”
A study published last month in the journal Nature Climate Change predicted that in the mid-2030s, there might be an “onset of rapid increases in the frequency of [high-tide flooding] in multiple US coastal regions.”
The report by the NASA Sea Level Change Team at the University of Hawaii factored in sea level rise due to manmade climate change as well as the effect on tides of changes in the moon’s orbit over an 18.6-year cycle.
The rapid increase in the number of high-tide flooding days could begin a little later in Boston, in the mid-2040s, the study suggested.
Such flooding is much more than a minor inconvenience, said Phil Thompson, director of the University of Hawaii Sea Level Center, who was part of the study.
“You might have a situation where a business might have its parking lot flooded 10 or 15 times in a month — that’s not a nuisance any longer. That’s a significant economic impact on that person,” Thompson said. “It’s really the accumulated impact of many small, seemingly minor issues. But when a minor issue occurs chronically, it becomes a bigger problem.”
Ben Hamlington, the NASA Sea Level Change Team’s lead, told the Washington Post, “The goal needs to be to try to limit global warming and keep the sea-level rise that we see as low-level as possible — for instance, by reducing our emissions — to reduce some of these impacts.”
Gregory Dusek, chief scientist at NOAA’s Center for Operational Oceanographic Products and Services, said in an interview that the study was “digging into more of the details and getting into more of the why” regarding the expected increase in high-tide flooding in coming decades, while NOAA’s focus was on “providing reliable information” on what to expect to the public.
David Abel of the Globe staff contributed to this report. Material from Globe wire services was included.
Martin Finucane can be reached at firstname.lastname@example.org.