2018 State of U.S. High Tide Flooding with a 2019 Outlook

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.