Rapid Growth, Record-Breaking Rise
Assessed over several decades, the national trend in high tide flooding frequency is accelerating, and is more than twice as likely now as it was in 2000. The rapid growth is in response to relative sea level rise, which is occurring along most U.S. coastlines. In 2019, relative sea level along coastlines reached an all-time record of 0.34 meters (1.1 feet) relative to 1920 levels—which is about four centimeters (1.5 inches) higher than it was in 2018.
The national annual high tide flooding frequency reached four days (median value) in 2019, just shy of the record of five days set in 2018. High tide flooding is now accelerating at 75 percent of NOAA tide gauge locations along the East and Gulf Coasts, with nearly all other locations rising, but not yet accelerating.
Compared to high tide flooding frequencies typical in 2000, 2019 was extraordinary. Flood days occurred 100 to 150 percent more frequently than in 2000 along the Northeast Atlantic and Eastern Gulf coastlines. Even higher percentage increases (more than 300 percent) occurred along the Southeast Atlantic (for example, more than a 500 percent increase in Charleston, South Carolina, with 13 days in 2019, compared to about two days in 2000). Percentage increases compared to 2000 were the greatest in the Western Gulf (more than 500 percent), followed by the Northeast and Southeast Atlantic coastlines and the Eastern Gulf.
During the 2019 season, water reached the flooding threshold a record-breaking number of times at 19 NOAA tide gauges along the Northeast Atlantic (nine days), Southeast Atlantic (seven days), the Eastern Gulf (three days), and the Western Gulf of Mexico (18 days) coastlines.
The New Normal
Next year (May 2020 to April 2021), acceleration in high tide flooding and its impacts are expected to continue. Nationally, the likely median outlook is two to six days. Regionally, the 2020 outlook is
- Six to 11 days along the Northeast Atlantic
- Five to 11 days along the Western Gulf
- Three to six days along the Southeast Atlantic
- Two to five days along the Eastern Gulf
By 2030, high tide flooding is likely to accelerate to a range of seven to 15 days. Frequent high tide flooding will continue to accelerate—with major impacts to infrastructure and the economy—unless coastal flood mitigation strategies are implemented or enhanced.