| 2018 State of U.S. High Tide Flooding with a 2019 Outlook - :20691 | National Ocean Service (NOS)
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2018 State of U.S. High Tide Flooding with a 2019 Outlook
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2018 State of U.S. High Tide Flooding with a 2019 Outlook
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    Tide gauges of the U.S. National Oceanic and Atmospheric Administration (NOAA) are measuring rapid increases in coastal flood risk along U.S. coastlines due to relative sea level (RSL) rise. The most noticeable impact of RSL rise is the increasing frequency of high tide flooding (HTF) that in 2018 was 1) disrupting vehicular traffic along the U.S. East Coast due to flooded roadways, 2) inhibiting parking and thus slowing commerce at stores in downtown Annapolis, Maryland, 3) raising groundwater elevations and degrading septic system functionalities in South Florida, and 4) salting farmlands within coastal Delaware and Maryland. In 2018, the national annual HTF frequency reached 5 days (median value) and tied the historical record set in 2015. HTF was most prevalent along the Northeast Atlantic Coasts (median of 10 days) and broke records within the Chesapeake Bay (e.g., 22 days in Washington D.C. and 12 days in Annapolis and Baltimore) and along the Eastern Gulf of Mexico Coasts with some major flooding from several hurricanes. In all, 12 individual (out of 98 U.S. tide gauge) locations broke or tied their HTF records. There are now over 40 locations whose HTF decadal trends reveal significant acceleration (nonlinear increase) and 25 locations whose HTF trends are linearly increasing, implying that impacts will soon become chronic without adaptation. HTF in 2019 is projected to be higher than normal at about 40 locations along the U.S. West and East Coasts in part due to a minor El Niño that is predicted to persist until early next year. The national median HTF frequency is projected to be more than 100% greater than it typically was in 2000. Regionally in 2019, the Northeast Atlantic is projected to experience a median of 8 days of flooding, which is a 140% increase since 2000. Flooding along the Southeast (5 days—190% increase over 2000), Eastern Gulf (3 days—100% increase since 2000) and Western Gulf (6 days—130% increase since 2000) Coasts continues to rapidly increase as well. The U.S. Southwest and Northwest Pacific Coasts are projected to see a median 2 and 6 days of flooding (80% and 20% increase since 2000), respectively. Annual flood records are expected to be broken again next year and for years and decades to come from RSL rise. Projecting out to 2030 and 2050 provides vital information for communities that are already taking adaptation steps to address coastal flooding impacts and those that are beginning to assess future flood risk in their communities. Bounded by a range of RSL rise under a lower and continued-high emission rate, today’s national HTF frequency of 5 days (national median) is likely to increase to about 7–15 days by 2030 and 25–75 days by 2050 (HTF range: low emission–high emission values), with much higher rates in many locations.

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