Here’s what you need to know about high tide flooding and its impact on Boston


Flooding at high tide can cause significant property damage and even force evacuations.

High tide flooding, like the one that inundated Long Wharf in Boston in January 2022, is expected to increase in frequency over time. (Craig F. Walker/Globe Staff)

Scientists from the National Oceanic and Atmospheric Administration predict that high tide flooding will occur with increasing frequency over the next few decades, which could have a huge impact on New Englanders.

According to NOAA, the northeast is particularly prone to tidal flooding, which means more flooded shorelines, streets and basements.

Last January, high tides flooded Long Wharf in downtown Boston.

According to NOAA, high tide flooding occurs when tides reach higher than normal levels and begin to dump ocean water onto streets or boil storm drains. It occurs when the tides reach between 1.75 and 2 feet above the daily mean high tide.

Boston had seven days of flooding at high tide last year, far less than the expected 11 to 18 days, but that trend is unlikely to continue.

As sea levels continue to rise, NOAA said, destructive flooding that only happened during a storm is now happening more regularly. They now occur during full moons or when there is a change in prevailing winds or currents.

NOAA predicts that by 2050, Boston could experience between 50 and 70 days of flooding at high tide.

“Coastal flood warnings for significant risks to life and property will become much more common as we approach mid-century,” the report said.

NOAA oceanographer William Sweet said Boston has fewer HTF days than expected because projections are based on what NOAA has recorded over the past few years, but certain circumstances can cause more or fewer HTF days. floods every year.

Last year, from May 2021 to April 2022, he said, we were still in a La Niña period, which is characterized by unusually cold ocean temperatures in the equatorial Pacific. During this time, winters are milder and storms tend to be further inland, meaning there is less opportunity for coastal flooding.

Additionally, Sweet said, we are in the slowing phase of the moon’s 18.6-year nodal cycle, which is causing the tides to drop. Sea levels in the northeast have also been lower, in general, in recent years, he said.

But experts predict sea levels in the northeast will rise again soon. After a few years of low sea levels, we should exit La Niña early next year, Sweet said.

That’s why NOAA still predicts 11 to 18 days of high tide flooding in Boston from May 2022 to April 2023, in its annual report.

The record number of high tide flood days ever recorded in Boston in a year was 22.

Elsewhere in New England, high tide flood days aren’t expected to be as many, but they’re still near record highs. Providence is expected to see six to 11 days, and the all-time high is 15. Newport, Rhode Island and Nantucket are expected to see three to seven days, and the all-time high is 11.

Sweet said sea levels are rising and causing more flood days at high tide due to some natural causes such as land subsidence, but largely due to climate change.

“Although the sea level continues to rise and fall every two years, the highs are increasing and the lows are not coming down as far,” Sweet said.

While minor flooding at high tide typically causes small disruptions such as road closures and stormwater backup, moderate flooding can damage homes and businesses, and major flooding can require evacuations, according to NOAA.

Massachusetts residents whose property is at risk from high tide flooding should consider getting more information about the risk for their specific property and researching ways to protect their property from flooding, Sweet said.

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