Multiple U.S. coastal regions may see rapid increases in the number of high-tide flooding days in the mid-2030s, according to a new study funded in part by CPO’s Modeling, Analysis, Predictions, and Projections (MAPP) program and co-authored by NOAA Satellites and NOAA's National Ocean Service. The combined effects of sea-level rise and natural fluctuations in tidal range are anticipated to cause tipping points in the frequency of high-tide flooding. These tipping points can produce acute impacts in underserved communities, who are often unprepared to deal with the consequences. 

The study is led by the University of Hawaiʻi at Mānoa and published in Nature Climate Change.

Coastal locations around the U.S., particularly along the Atlantic coast, are experiencing recurrent flooding at high tide. The impact of high-tide flooding accumulates over numerous, seemingly minor occurrences, which can exceed the impact of rare extremes over time. These impacts are subtle—for example, the loss of revenue due to recurrent road and business closures—compared with the physical damage of property and infrastructure associated with extreme storm-driven events. 

The research team analyzed tide gauge data from 89 coastal locations around the U.S., including 10 locations from Hawaiʻi and U.S.-Affiliated Pacific Islands, and developed a novel statistical technique that combined changes in tidal range with NOAA sea-level rise scenarios for the 21st century to produce the projections of high-tide flooding. 

Continued sea-level rise will exacerbate the issue where present, and many more locations will begin to experience recurrent high-tide flooding in the coming decades. The authors expect the most rapid increases to be along the U.S. Pacific and Gulf of Mexico coastlines, which includes Hawaiʻi and other Pacific Islands. Additionally, the research team found that annual cycles in tides and sea level can combine with oceanographic anomalies to produce many high-tide flooding episodes over a short amount of time—creating extreme months with clustered events.

The authors believe that the mid-2030s will mark the onset of an expected transition in high-tide flooding from a regional issue to a national issue, with the majority of U.S. coastlines being affected.

The study demonstrates that it is important to plan for extreme months or seasons during which the number of flooding episodes, rather than the magnitude, is exceptional.

Read the paper »