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U.S. approaching ‘tipping points’ for sea level rise-related flooding earlier than expected


Most of U.S. coast may see 30 or more days a year of floods up to two feet above high tides

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

Annapolis, Maryland, pictured here in 2012, is one of three major East Coast urban areas already being faced with nuisance flooding in excess of 30 days per year. Credit: Amy McGovern

The new study establishes a frequency-based 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 used a 0.5 to 1.2 meters (1.5 to four foot) set of recent projections for global sea level rise by year 2100 similar to the rise projections of the Intergovernmental Panel for Climate Change, but also accounting for local factors such as the settlement of land, known as subsidence.

Based on that standard, the team found 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, presented at a press conference today at the AGU Fall Meeting in San Francisco, 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.

“Coastal communities are beginning to experience sunny-day nuisance or urban flooding, much more so than in decades past,” said William Sweet, oceanographer at NOAA’s Center for Operational Oceanographic Products and Services (CO-OPS) in Silver Spring, Maryland, and lead author on the study.

“This is sea level rise. Unfortunately, once impacts are noticed, they will become commonplace rather quickly. We find that in 30-40 years even modest projections of global sea level rise – 1.5 feet by 2100 – will increase instances of daily high tide flooding to a point requiring an active, and potentially costly, response and by the end of this century, our projections show that there will be near-daily nuisance flooding in most of the locations that we reviewed.”

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.; Norfolk, Virginia; and Wilmington, North Carolina; 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.

“As communities across the country become increasingly vulnerable to water inundation and flooding, effective risk management is going to become more heavily reliant on environmental data and analysis,” noted Holly Bamford, NOAA acting assistant secretary for conservation and management.

“Businesses, coastal managers, federal, state, and local governments, and non-governmental organizations can use research such as this as another tool as they develop plans to reduce vulnerabilities, adapt to change, and ensure they’re resilient against future events.”

“The importance of this research is that it draws attention to the largely neglected part of the frequency of these events. This frequency distribution includes a hazard level referred to as ‘nuisance’: occasionally costly to clean up, but never catastrophic or perhaps newsworthy,” said Earth’s Future editor Michael Ellis, Head of Climate Change Science at the British Geological Survey in Nottingham, United Kingdom, in accepting the paper for the online journal.

Ellis also observed that “the authors use observational data to drive home the important point that nuisance floods (from inundating seas) will cross a tipping point over the next several decades and significantly earlier than the 2100 date that is generally regarded as a target date for damaging levels of sea-level. The paper also raises the interesting question of what frequency of ‘nuisance’ corresponds to a perception of ‘this is no longer a nuisance but a serious hazard due to its rapidly growing and cumulative impacts’.”

Notes for Journalists

Journalists and public information officers (PIOs) of educational and scientific institutions who have registered with AGU can download a PDF copy of this article by clicking on this link:

Or, you may order a copy of the final paper by emailing your request to Kate Wheeling at Please provide your name, the name of your publication, and your phone number.

Neither the paper nor this press release is under embargo.
“From the Extreme to the Mean: Acceleration and Tipping Points of Coastal Inundation from Sea Level Rise”

William Sweet: NOAA National Ocean Service, Center for Operational Oceanographic Products and Services, Silver Spring, MD, USA;

Joseph Park: NOAA National Ocean Service, Center for Operational Oceanographic Products and Services, Silver Spring, MD, USA.

Contact information for the authors:
William Sweet: +1 (301) 713-2890 x218,

AGU Contact:
Kate Wheeling
+1 (202) 531-3729

NOAA Contact:

Keeley Belva
+1 (301) 713-3066

Peter Weiss | American Geophysical Union
Further information:

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