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Flooding tipping points earlier than expected for U.S. coasts

By 2050, most of the U.S. coast is likely to see 30 or more days of flooding a year due to dramatically accelerating impacts from sea level rise, says a new study.

A man walks along cars on a flooded Croft Pl as Staten Island suffers flooding and damage by Hurricane Irene that pass through the New York City area.  Image Credit: Mark Bonifacio  New York Daily News

A man walks along cars on Staten Island after Hurricane Irene passed through the New York City area in 1999. Image Credit: Mark Bonifacio New York Daily News

By 2050, a majority of U.S. coastal areas – including dozens of cities – are likely to be threatened by 30 or more days of flooding each year due to dramatically accelerating impacts from sea level rise. That’s according to a study published December 18 in Earth’s Future, a journal of the American Geophysical Union.

The new study establishes a benchmark for what the authors call “tipping points” for when so-called nuisance flooding — flooding between 0.3 to 0.6 meters (one to two feet) above local high tide — occurs 30 or more times a year.

The study suggests that that these tipping points will be met or exceeded by 2050 at most of the U.S. coastal areas studied, regardless of sea level rise likely to occur this century. According to the study authors, these regional tipping points will be surpassed in the coming decades in areas with more frequent storms, or areas where local sea levels rise more than the standard global projection of 0.5 to 1.2 meters (1.5 to four feet). This also includes coastal areas like Louisiana where subsidence is causing land to sink below sea level.

The new study, used data from NOAA tide gauges to show the annual rate of daily nuisance floods has drastically increased, even accelerating in recent years. This type of flooding is now five to 10 times more likely today than 50 years ago.

NOAA oceanographer William Sweet is lead author on the study. He said:

Coastal communities are beginning to experience sunny-day nuisance or urban flooding, much more so than in decades past. This is sea level rise. Unfortunately, once impacts are noticed, they will become commonplace rather quickly.

The scientists base the projections on NOAA tidal stations where there is a 50-year or greater continuous record. The study does not include the Miami area, as the NOAA tide stations in the area were destroyed by Hurricane Andrew in 1992 and a continuous 50-year data set for the area does not exist.

Based on that criteria, the NOAA team is projecting that Boston, New York City, Philadelphia, Baltimore, Washington, D.C.as well as Norfolk, Virginia, Wilmington, North Carolina, and areas all along the Mid-Atlantic coast, will soon make, or are already being forced to make, decisions on how to mitigate these nuisance floods earlier than planned. In the Gulf, NOAA forecasts earlier than anticipated floods for Galveston Bay and Port Isabel, Texas. Along the Pacific coast the earlier impacts will be most visible in the San Diego/La Jolla and San Francisco Bay areas.

Mitigation decisions could range from retreating further inland to coastal fortification or to a combination of “green” infrastructure using both natural resources such as dunes and wetland, along with “gray” man-made infrastructure such as sea walls and redesigned storm water systems.

Bottom line: According to a December 18, 2014 study in Earth’s Future, a majority of U.S. coastal areas – including dozens of cities – are likely to be threatened by 30 or more days of flooding each year due to dramatically accelerating impacts from sea level rise by 2050.

Read more from the AGU

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