NOAA: Flood risk rising with high tides

RYAN HUTTON/Staff file photoVehicles navigate a partly flooded Bridge Street in Salem in March 2018. The national frequency of high-tide flooding in U.S. coastal communities escalated again in 2020 and researchers expect that trend to continue into 2022 and for decades beyond, according to NOAA’s annual report and outlook on high-tide flooding.

The national frequency of high-tide flooding in U.S. coastal communities escalated again in 2020 and researchers expect that trend to continue into 2022 and for decades beyond, according to NOAA’s annual report and outlook on high-tide flooding.

The report, released Wednesday, said the median national rate of high-tide flooding in the period between May 2020 and April 2021 rose to four days per year — a rate twice what it was 20 years ago.

The report’s conclusions are drawn from data culled from 97 tide gauges operated by the National Oceanic and Atmospheric Administration throughout the coastal U.S.

The data for the upper Northeast Atlantic region was not as dire as other regions, such as locations along the Southeast coastal U.S. and the coastlines of the Gulf of Mexico.

Data from the tidal gauge located in Boston indicated the area experienced 11 high-tide flood days between May 2020 and April 2021. That is well above the six high-tide flood days experienced in 2006, but well below the region’s record of 22.

William Sweet, an oceanographer with NOAA’s National Ocean Service and one of the authors of the report, conceded Boston’s data was lower than the national trends.

But, he said, the agency expects the “underlying acceleration” will continue.

“Sea levels are going up more than anticipated and high-tide flooding is following suit,” Sweet said.

NOAA’s outlook projects 11 to18 high-tide flood days for the Boston area in 2021, 30 to 35 high-tide flood days by 2030 and 45 to 95 high-tide flood days by 2050.

High-tide flooding largely is caused by unrelenting rises in sea levels that can create flooding — sometimes called sunny-day flooding or nuisance flooding — without the engine of a powerful storm. Instead, the flooding may occur fueled only by a combination of a full moon, tides and wind currents.

The high-tide flooding has a particularly onerous impact on surface and sub-surface infrastructure, such as roadways, storm- and wastewater systems and transportation systems.

NOAA said the southeast coastal U.S., and the coastlines of the Gulf of Mexico experienced the greatest 2020 increases — in some cases between 400% and 1,100% — in the frequency of high-tide flooding.

The agency said 14 locations in those regions tied or set records for the number of high-tide flooding days and attributed those increases to a record-breaking hurricane season and rising sea levels. 

Contact Sean Horgan at 978-675-2714, or shorgan@gloucestertimes.com. Follow him on Twitter at @SeanGDT.

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