East Cost "nuisance" flooding already increasing

By 2050, much of U.S. coastal areas are likely to be threatened by 30 or more days of flooding annually because of dramatically accelerating impacts from sea-level rise, according to a new National Oceanic and Atmospheric Administration (NOAA) study.

The findings appear in a paper entitled “From the Extreme to the Mean: Acceleration and Tipping Points for Coastal Inundation due to Sea Level Rise” and follows an earlier study by the report’s co-author, William Sweet, Ph.D., a NOAAA oceanographer.

Sweet and fellow NOAA scientist Joseph Park established a frequency-based benchmark for what they call “tipping points,” when so-called “nuisance flooding,” defined by NOAA as between 1 and 2 feet above local high tide, occurs 30 or more times a year.

“Coastal communities are beginning to experience sunny-day nuisance or urban flooding, much more so than in decades past,” Sweet said. “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 will increase instances of daily high-tide flooding to a point requiring an active, and potentially costly, response.”

Based on that standard, the NOAA 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. In their study, Sweet and Park used a 1.5- to 4-foot set of recent projections for global sea-level rise by 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.

Chart shows that Boston could start experiencing nuisance flooding by 2021, and Providence and New London, Conn., a decade later. (NOAA)

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