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2020 Outlook from NOAA: Sea Level Rise to Drive Chronic High Tide Flooding

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U.S. Soldiers from the 59th Aviation Troop Command, South Carolina Army National Guard, provide airborne support during flood relief operations in Columbia, S.C., Oct. 5, 2015. Photo by Staff Sgt. Roberto Di Giovine

By Marc Kodack

The National Oceanic and Atmospheric Administration recently published their 2018 State of High Tide Flooding and 2019 Outlook. The 2019 outlook covers the meteorological year which runs from May 2019-to-April 2020. High tide flooding (HTF), also known as nuisance or sunny-day flooding (both euphemisms these days), occurs in the absence of any storms, such as when there is a strong wind coming off the ocean at the same time as a high tide. High tide flooding is a direct result of rising sea levels. Nuisance flooding and sea level rise are already affecting multiple, coastal Department of Defense installations, as highlighted by the Pentagon this past January, and the Center for Climate and Security’s Military Expert Panel report “Sea Level Rise and the U.S. Military’s Mission.” Thus, NOAA’s projection that nuisance flooding trends will continue to linearly increase resulting in chronic flooding rather than sporadic flooding will increase disruptions of portions of some installations more frequently, e.g., flooded roads, clogged stormwater drains that may flood facilities.

For 2019 meteorological year, NOAA projects that 42 locations on the west and east coasts, may experience higher flooding frequencies than the average. Two of these locations San Diego and Norfolk, have large Navy shore installations and facilities. The Northeast Atlantic region is expected to experience the highest median number of high tide flood events of either coast with 8 days, although specific locations, such as Norfolk, may experience, 10-15 days. For the southwest Pacific coast, 2 days of high flood events are expected, with San Diego possibly experiencing 5-9 days. In general, “the 2019 HTF outlook is expected to be over 100% greater (median value) than would have been typical in year 2000.” For example, since May 2019, in Norfolk, local newspaper stories have reported on two separate tidal related flooding events at the beginning and middle of October 2019. A king tide occurred at the end of October, which caused low lying areas to flood. In and around San Diego, king tides also regularly flood low lying areas. The most recent king tide was in January 2019. The next king tides will occur in mid-January and mid-February 2020. It is unknown what the threshold is for reporting of nuisance flooding by local newspapers and television stations in both Norfolk and San Diego. Thus, lower-then-the-reporting-level-threshold nuisance flooding may occur more frequently, but is not reported by the media.

NOAA also modelled regional median values for HTF on both the west and east coasts for 2030 and 2050. For example, the Northeast Atlantic region will experience 15-20 days of HTF at 2030 and 40-130 days of HTF at 2050. Under the intermediate climate scenario used, Norfolk may experience 170 days a year of HTF.

With the increasing occurrence of HTF, DoD’s coastal installations need to determine how these events will affect their infrastructure, facilities, and the operations that are performed in these facilities to minimize disruptions. Infrastructure planning will be even more complicated when HTF is combined with forecasts for the occurrence and intensity of tropical storms or hurricane events that may strike.

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