Sea Level Rise and Nuisance Flood Frequency Changes Around the U.S.

This technical report from National Oceanic and Atmospheric Administration (NOAA) describes the increased rate and severity of recurrent coastal flooding events as related to sea level rise. It also addresses what climatic patterns are associated with year-to-year differences in flooding, and during what season nuisance floods typically occur and why. 

NOAA water level gauges have been measuring water levels around the U.S. for over a century. Their observations clearly show that much of the U.S. is experiencing long-term relative sea level rise (https://tidesandcurrents.noaa.gov/). Not only are extreme flooding events reaching higher grounds and covering larger areas, the frequency and duration of these extreme flood events are increasing.

There are approximately 75 NOAA gauges around the U.S. with empirically defined flood level thresholds, and of those, 45 gauge records were analyzed. The report describes the findings of how water levels above the elevation threshold for “minor” coastal flooding (nuisance level) impacts established locally by the National Weather Service have been increasing in time. Event frequencies are accelerating at many U.S. East and Gulf Coast gauges, and many other locations will soon follow regardless of whether there is an acceleration of sea level rise. Additionally, they found a regional pattern of increasingly greater event-rate acceleration as the height between mean sea level and a location’s nuisance flood threshold elevation decreases.

The report concludes that there is a time horizon, largely dependent upon the local rate of sea level rise, when critical elevation thresholds for various public/private/commercial serving systems will become increasingly compromised by tidal flooding. It is stressed that in many areas, the frequency of nuisance flooding is already on an accelerating trajectory, and many other locations will soon follow even with a continuation of current linear sea level rise rates.

 

Publication Date: June 2014

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