Topping the list of locations that set high-tide flooding records were Boston and Atlantic City, which flooded on 22 days, and Sabine Pass and Galveston, Tex., which flooded on 23 and 18 days, respectively.
Boston observed its highest and third-highest tides on record in January and March when strong nor’easters battered southern New England.
Over the past year, NOAA said the combination of long-term sea level rise and the very active nor’easter and hurricane seasons made a number of flooding events “more impactful.” Four nor’easters hammered the Northeast in March and the 2017 Atlantic hurricane season was among the most active on record for landfalling storms.
It is not just during big storms that the ever-rising tides have profound effects on coastal communities. So-called “sunny day” or “nuisance” flooding is also dramatically increasing in frequency, which occurs during certain moon phases.
“As relative sea-level increases, it no longer takes a strong storm or a hurricane to cause coastal high tide flooding,” NOAA’s summary of the report said. “High tide flooding causes frequent road closures, overwhelmed storm drains, and compromised infrastructure.”
The record high-tide flooding seen in the 2017 meteorological year, spanning May 2017 to April 2018, fits into a long-term increase in water levels, which has shown acceleration in recent years. “The U.S. average high tide flood frequency is now 50 percent greater since 2000 and 100 percent greater than it was 30 years ago,” the NOAA report said.
Some of the fastest change has occurred along the Mid-Atlantic coast. In 15 years, the incidence of high-tide flooding in the Mid-Atlantic doubled, from an average of three days per year in 2000 to six in 2015, according to a separate NOAA report published in February.
Looking ahead to the next year, through April 2019, the report projects another year of intensified high-tide flooding.
“The projected increase in high tide flooding in 2018 may be as much as 60 percent higher across U.S. coastlines as compared to typical flooding about 20 years ago and 100 percent higher than 30 years ago,” the report’s summary said. “This is due to long-term sea-level rise trends and, in part, by El Niño conditions that may develop later this year.”
NOAA’s February report on high-tide flooding made even more dramatic projections for the middle and latter parts of this century, when high-tide flooding could occur every other day in many coastal locations.
The announcement on the past year’s record high-tide flooding was incorporated into the bottom of a report that declared it was the nation’s warmest May on record.
Neither the announcement of the high-tide flooding record, the accompanying summary nor the technical report mention the words “climate change,” which scientists widely believe is the underlying cause of sea-level rise and the increasing tides.