El Niño & rising seas bring record nuisance flooding

Southeast, Gulf Coast hit especially hard

Nuisance flooding set new records during the past year, according to a new NOAA report. @bberwyn photo.
Nuisance flooding set new records during the past year, according to a new NOAA report. @bberwyn photo.

Staff Report

There’s no question that nuisance flooding is increasing along U.S. coasts due to sea level rise, and some coastal residents got their feet frequently during the past year, according to a new report from the National Oceanic and Atmospheric Administration.

In some cities, the days of nuisance flooding during the past meteorological year (May 2015 to April 2016) flooding exceeded trends and broke records, especially in the southeastern U.S and Gulf Coast. For those areas, the strong El Niño may have exacerbated the effects of rising sea level.

Wilmington, North Carolina, saw an all-time high of 90 days of nuisance flooding, nearly one quarter of the year. Other cities with record numbers of flooding days are Charleston, South Carolina; Port Isabel, Texas; Mayport, Virginia Key, Key West, and Fernandina Beach, Florida, the report said.

Some cities in the Mid-Atlantic and West Coast also experienced greater tidal flooding frequencies above normal trends, including Norfolk, Virginia; Baltimore, Maryland; and San Francisco and La Jolla, California.

Nuisance flooding, which causes such public inconveniences as frequent road closures, overwhelmed storm drains and compromised infrastructure, now occurs with high tides in many locations due to climate-related sea level rise, land subsidence, and the loss of natural barriers.

The new tally is part of an ongoing effort to track nuisance flooding led by  NOAA scientists William Sweet, Ph.D., and John Marra, Ph.D.

“Sea level rise is continuing and flooding impacts are happening now,” said Sweet, an oceanographer with NOAA’s Center for Operational Oceanographic Products and Services. “The upward trend in nuisance flooding is an ongoing issue. Last year we broke several records, and trends show that we’ll likely continue to do so in the future. Coastal communities should expect a new normal in nuisance tidal flooding and prepare for potential impacts.”

The new report also provides a new outlook for the 2016 meteorological year, taking into account the La Niña conditions anticipated to develop in the coming months. La Niña typically has less effect on tidal flood frequencies compared to El Niño, however the nuisance flooding trend is still increasing.

The outlook for 2016 shows that the cities with the highest frequency of nuisance flooding will likely be:

  • Annapolis, Maryland, with 47 days
  • Wilmington, North Carolina, with 42 days
  • Washington, D.C., with 30 days
  • Charleston, South Carolina, with 27 days
  • Atlantic City and Sandy Hook, New Jersey, with 26 days

Along the California coast, less than 10 days are expected at La Jolla and San Francisco, a decrease from 13 and 20 days observed in 2015, respectively.

Nuisance flooding is increasing along U.S. coasts due to sea level rise. The extent of nuisance flooding depends on multiple factors, including topography and land cover. The study defines nuisance flooding as a daily rise in water level above minor flooding thresholds set locally by NOAA weather forecasters and emergency managers for coastal areas prone to flooding.

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