Break out the galoshes.
The projected increase in high tide flooding in 2018 may be as much as 60 percent higher across U.S. coastlines compared to typical flooding about 20 years ago, according to scientists at the National Oceanic and Atmospheric Administration.
Some flooding in the 2018 seasonal forecast can be credited to an El Nino scientists now believe may occur later this year, however, they believe sea level rise is the main culprit for an increase in recent years in coastal high tide flooding, which occurs when water levels measured at NOAA’s numerous tide gauges exceed heights based on national flooding thresholds.
These assertions were made by NOAA scientists in the 2017 State of U.S. High Tide Flooding and a 2018 Outlook, which shows more than a quarter of the coastal locations measured last year tied or broke their individual records for high tide flood days.
“I think the underlying trend is quite clear. Due to sea level rise, the national average trend in high tide flood frequency is now more than 50 percent higher than it was 20 years ago and 100 percent higher than it was 30 years ago,” William Sweet, a NOAA oceanographer and one of the authors of the report, said on a conference call with reporters.
Sweet noted that the sea level is rising globally up to 3 mm or more per year, or roughly 1 inch every eight years, one-third of which he attributes to thermal expansion of the ocean while two-thirds is from land-based ice melt.
These rising seas contributed to the number of days of high tide flooding last year reaching a historical record.
“2017 was a record breaker,” Sweet said.
Expect more records to fall this meteorological year, which is measured between May 2018 and April 2019.
“For 2018, records are expected to continue to be broken,” Sweet said.
However, this year’s expected record coastal flooding can’t be placed entirely on the shoulders of sea level rise.
“An El Nino is possible in late 2018 into early 2019,” Sweet said.
El Ninos typically bring warmer ocean water and higher sea levels along the West Coast, and along the East Coast, the phenomenon tends to drive more frequent wind events, or nor’easters. NOAA is forecasting higher than expected flood frequencies at 48 West and East Coast locations.
Fellow report author Gregory Dusek, a chief scientist at NOAA’s Center for Operational Oceanographic Products and Services, said they were able to use data at an increased number of NOAA tide gauges in this report, providing them more data than before.
NOAA’s 210 tide gauges around the U.S. provide a long-run tidal history. Many of the gauges have been in operation since the early 1900s, according to Dusek.
“Several of them have data records exceeding 100 years of data,” he added.
Dusek used a NOAA gauge first installed around Charleston, S.C., in 1921 as an example of what the data in the report shows.
By the time the infamous 1928 Okeechobee hurricane rolled in to Charleston, it was a Category 1 that caused significant damage and flooding in the area. The gauge there measured an elevation of .75 meters above the mean high tide value – the highest that was observed from 1921 to 1934.
“Now fast forward to last year, where we exceeded that value four times in Charleston, and we’re expected to exceed it at least four times this year,” Dusek said.
Such coastal flooding is increasing in “frequency, depth and extent” in numerous U.S. areas due to ongoing increases in local relative sea level, according to the report.
The top five cities that saw the highest number of flood days across the U.S. and broke records include Boston; Atlantic City, N.J.; Sandy Hook, N.J.; Sabine Pass, Texas; and Galveston, Texas.
“These cities faced the brunt of an active nor’easter and hurricane seasons and sea level rise, which has made these and other less extreme events more impactful,” the report states.
The report finds, for example, that the Southeast Atlantic coast is experiencing the fastest rate of increase in annual high tide flood days, with more than a 150 percent increase since 2000 predicted in this year at most locations.
According to the report, we can expect the breaking of annual flood records next year and for decades to come as sea levels rise, and likely at an accelerated rate.
“Already, high tide flooding that occurs from a combination of high astronomical tides, typical winter storms and episodic tropical storms has entered a sustained period of rapidly increasing trends within about two-thirds of the coastal U.S. locations,” the report states. “Though year-to-year and regional variability exist, the underlying trend is quite clear: due to sea level rise, the national average frequency of high tide flooding is double what it was 30 years ago.”
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