NOAA warns of flood risk

ELLSWORTH — A majority of coastal areas in the United States are likely to be threatened by flooding 30 or more days each year by 2050 because of accelerating impacts from sea level rise, according to a National Oceanic and Atmospheric Administration report released last week.

The findings of the study by a pair of NOAA scientists were presented at a meeting of the American Geophysical Union last week in San Francisco.

NOAA scientists William Sweet and Joseph Park established a frequency-based benchmark for what they call “tipping points,” when so-called nuisance flooding occurs more than 30 or more times a year.

Nuisance flooding, defined by NOAA’s National Weather Service as between 1 to 2 feet above local high tide, is already a problem in some places.

Washington, D.C., is one of three major East Coast urban areas – Annapolis and Wilmington, N.C., are the others – already being faced with nuisance flooding more than 30 days a year.

The NOAA team found that by 2050 this tipping point will be met or exceeded in most of the coastal areas studied, regardless of sea level rise likely to occur this century. Sweet and Park used a 1.5-to-4-foot set of recent projections for global sea level rise by the year 2100 similar to those of the Intergovernmental Panel for Climate Change, but also accounting for local factors such as the subsidence of land.

According to the report, regional tipping points will be surpassed in the coming decades in areas with more frequent storms and where local sea levels rise more than the global projections.

This includes coastal areas such as Louisiana, where subsidence that is not a result of by climate change is causing land to sink below sea level.

NOAA tide gauges show the annual rate of daily floods reaching these levels has increased drastically – often accelerating – and floods are now five to ten times more likely today than they were 50 years ago.

“Coastal communities are beginning to experience sunny-day nuisance or urban flooding, much more so than in decades past,” Sweet said in an announcement of his findings. “This is due to sea level rise.

“Unfortunately, once impacts are noticed, they will become commonplace rather quickly. We find that in 30 to 40 years, even modest projections of global sea level rise – 1.5 feet by the year 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.”

If the NOAA findings are correct, communities across the country will become increasingly vulnerable to flooding. Effective risk management will become more heavily reliant on environmental data and analysis, according to Holly Bamford, NOAA’s 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,” Bamford said.

The scientists based 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.

The NOAA team is projecting that in addition to the nation’s capital and Wilmington, Boston, New York City, Philadelphia, Baltimore and Norfolk, Va., will soon be, or are already being forced to, make decisions on how to mitigate these nuisance floods earlier than planned.

In the Gulf of Mexico, 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.

All of those decisions are likely to be both expensive and controversial.

Stephen Rappaport

Stephen Rappaport

Waterfront Editor at The Ellsworth American
Stephen Rappaport has lived in Maine for nearly 30 years. A lifelong sailor, he spends as much time as possible messing about in boats. [email protected]

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