Tidal ‘Nuisance Flooding’ On The Rise In Coastal Cities As Sea Level Inches Upward

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Climate change isn’t always just catastrophic. It can also be a nuisance.

A new report from the National Oceanic and Atmospheric Administration (NOAA) this week found that nuisance flooding, or minor flooding, has increased on all three U.S. coasts between 300 and 925 percent since the 1960s. The report, Sea Level Rise and Nuisance Flood Frequency Changes around the United States, identified eight of the top ten U.S. cities to experience this increase in flooding, which is due to rising sea levels, as being on the East Coast.

Nuisance flooding can cause road closures, overwhelm storm drains, and damage infrastructure. While extreme storms like Hurricane Sandy wreak havoc for days and leave detrimental damage in their wake, nuisance flooding is less headline-inducing but far more common. So-called “nuisance days” increased in Annapolis and Baltimore, Maryland by more than 920 percent according to the study. Philadelphia saw an increase of 650 percent and both Washington, D.C. and San Francisco increased around 375 percent. The study looked at 45 tide gauges along the shoreline, finding that 41 locations increased in frequency with the highest being along the mid-Atlantic coast.




“As relative sea level increases, it no longer takes a strong storm or a hurricane to cause flooding,” William Sweet, an oceanographer at NOAA and the report’s lead author, said in a statement. “The effects of rising sea levels along most of the continental U.S. coastline are only going to become more noticeable and much more severe in the coming decades, probably more so than any other climate-change related factor.”

Sweet said that flooding is now occurring along with high tides in many locations due to climate-related sea level rise, land subsidence, and the loss of natural barriers. The study defines nuisance flooding as a daily rise in water level above the minor flooding threshold set locally by NOAA’s National Weather Service.

The study warns that coastal infrastructure will become increasingly compromised by tidal flooding, and faces a “time horizon” depending on how fast sea level rises. “When that day comes, these impacts are going to be accelerated,” Sweet said, “and that’s going to spell all sorts of issues for communities when it comes to adaptation and resilience.”

Global mean sea level continued to rise during 2013 on pace with a trend of 3.2 ± 0.4 mm per year over the past two decades. Since 1870, global sea level has jumped by about 8 inches. According to the EPA, a two-foot rise in global sea levels by 2100 would result in a rise of 2.3 feet in New York City, 2.9 feet at Hampton Roads, Virginia, 3.5 feet at Galveston, Texas, and one foot at Neah Bay in Washington state. Warming of the oceans and loss of glaciers and ice sheets both contribute to sea level rise. The IPCC predicts a global sea level rise between 1.7 and 3.2 feet by the year 2100.

Another recent analysis by Reuters found that that number of days per year that tidal waters reached or exceeded NOAA thresholds more than tripled in many places along the East Coast over the last four decades. The review of 25 tidal gauges found that since 2001 water has reached flood levels an average of 20 days or more a year in a number of cities, including Wilmington, North Carolina; Atlantic City, New Jersey; and Charleston, South Carolina.