New data shows 'extraordinary' rise in US high-tide flooding

WASHINGTON • Parts of the United States saw record levels of high-tide flooding last year as rising seas brought water farther into coastal homes and infrastructure, government scientists reported on Tuesday.

The increase in high-tide flooding along the Atlantic and Gulf coasts since 2000 has been "extraordinary", the National Oceanic and Atmospheric Administration (NOAA) reported, with the frequency of flooding in some cities growing five times in that period.

That shift is damaging homes, imperilling the safety of drinking water, inundating roads and otherwise hurting coastal communities, the agency said.

"Conditions are changing, and not just in a few locations," said Ms Nicole LeBoeuf, acting assistant administrator for NOAA's National Ocean Service, which compiled the report.

"Damaging floods that decades ago happened only during a storm now happen more regularly, even without severe weather."

NOAA defines high-tide flooding, also called sunny-day or nuisance flooding, as water rising more than half a metre above the normal daily high-tide mark.

The frequency of that flooding has increased because of rising sea levels, which were roughly 30cm higher nationally last year than in 1920.

The number of days with high-tide flooding set or tied records in 19 places around the country last year, including Corpus Christi, Texas, which recorded 18 days of flooding; Galveston, Texas (18 days); Annapolis, Maryland (18 days); and Charleston, South Carolina (13 days).

The place with the greatest number of recorded flood days was Eagle Point, Texas, in Galveston Bay - it reported high-tide flooding on 64 days, or almost one in every six days.

Those numbers represent huge jumps in a short period. In 2000, Corpus Christi had just three days of tidal flooding; Charleston had two. The report notes that Charleston recorded just 13 days of high-tide flooding in the more than 50 years that measurements were first kept - the same number that occurred last year alone.

That trend is likely to accelerate, the agency said.

By 2030, NOAA projected, the frequency of high-tide flooding could double or treble. By 2050, it said, that number could be five to 15 times as great, with the typical coastal community flooding between 25 and 75 days a year.

The new data comes as the Trump administration continues to play down the threat of global warming, which is the driving factor behind sea-level rise.

President Donald Trump is pulling the US out of the Paris climate accord, and his officials have cited the coronavirus pandemic in efforts to weaken crucial environmental provisions.

"Climate change and carbon emissions are a factor at play when we look at how tides are rising," said Ms LeBoeuf.

NYTIMES