NOAA predicts up to 18 days of high tide flooding for Boston next year

National Oceanic and Atmospheric Administration (NOAA) scientists say they expect high tide flooding along the East Coast to accelerate as sea levels rise.

In most coastal areas of the United States, the number of high tide flood days per year is increasing. It’s actually accelerating along most of the eastern and Gulf coasts,” NOAA oceanographer William Sweet said at a press conference on Tuesday.

“Around two-thirds of sites experienced similar or more high-tide flood days than the previous year, and the flood rate is more than double what it was around 20 years ago.

NOAA predicts 11 to 18 days of flooding at high tide for Boston next year, although the city experienced fewer flood days than expected last year, according to an annual report released Tuesday. Boston only experienced seven days of high tide flooding from May 2021 to April 2022, instead of the predicted 11 to 18 days.

Forecasts for other New England cities for next year include 6-13 days for Portland, ME; 6-11 days to Providence, RI and 3-7 days to New London, CT.

Sometimes called “nuisance” or “sunny weather” flooding, high tide flooding occurs when water exceeds the average daily high tide for at least one hour, spilling onto streets and sidewalks.

Flooding at high tide endangers crucial infrastructure in Boston, including stormwater systems and public transportation, as well as low-lying areas like Long Wharf and Morrissey Boulevard.

Fewer high-tide flood days than expected last year are likely due — at least in part — to the moon’s natural cycle, Sweet said.

The Moon’s orbit around the Earth gradually shifts about five degrees every 18.6 years. This “lunar nodal cycle” – sometimes referred to as the “moon swing” – can either dampen or increase the overall height of the tides. We are currently in a “dampening” phase that will end around 2027. From 2028 to 2036, scientists expect the moon’s shifting orbit to lead to higher tides and a risk of flooding. amplified.

“In the northeast, there’s been a bit of a respite,” Sweet said. “The tides just aren’t as high as they were several years ago. But this swing will bottom out and start to rise again.”

A 2022 UMass report on climate change impacts for Greater Boston notes that eight of Boston’s top ten flood events — including the devastating Nor’easters of winter 2018 — occurred during a peak in that cycle. lunar.

Sandbags hold back water at the entrance to the MBTA Aquarium station during a 2018 northeast. (Robin Lubbock/WBUR)

According to the NOAA report, three coastal communities in the United States set or equaled records for high tide flood days last year. Reedy Point, DE saw six days of high tide flooding, one more than the previous year; Kwajalein Island in the Marshall Islands observed four days of high tide flooding, also one more than in 2021. The Springmaid Pier, SC water level station near Myrtle Beach matched its 2021 record with 11 days of flooding at high tide.

Boston’s record for high tide flooding was set in 2009 and 2017, with 22 days recorded each year.

According to the 2022 UMass report, sea level rise could lead to harmful flooding in Boston nearly 180 days per year by 2050. Boston has one of the highest rates of sea level rise in the world, in part because the earth is sinking about six inches every hundred years as it continues to adjust since the last Ice Age.

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