A Multi-decadal Coastal Water Level Model Reanalysis for Coastal Inundation and Flood Risk Assessment

With losses mounting from coastal flooding and associated impacts, better information on
present and future coastal flood risk is needed by stakeholders ranging from the military to state
and local governments who collectively oversee trillions of dollars of coastal infrastructure;
small to large businesses in coastal economies; and roughly half of the US population who live in
coastal areas. Available flood risk information is largely limited to present day 1% and 0.2%
annual chance flood levels from the FEMA National Flood Insurance Program, does not take
into account ongoing Sea Level Rise (SLR), and is insufficient for future planning. For example,
due to SLR the national rate of minor, but disruptive, high tide flooding has doubled since about
2000 and is accelerating in over 40 coastal locations (Sweet et al, 2020). An authoritative source
of coastal flood likelihood information is needed that will support assessments of contemporary
(baseline) risk of various coastal ocean and flood hazard levels (e.g., 10%, 20%, 99% annual
chance events; NOAA NWS minor, moderate and major coastal flood thresholds) along U.S.
coastlines sufficient to inform a variety of decisions. The basis for such an assessment requires a
multi-decadal reanalysis of coastal water levels that is well validated to NOAA tide gauge
records.
This project will compute a sequence of multi-decade (1979-2019) coastal water reanalyses
using the ADCIRC storm surge, tide, and wind-wave model, driven by long-term meteorological
reanalyses from NOAA and ECMWF. Predicted coastal water levels along the US eastern and
Gulf of Mexico coasts will be compared to NOAA NWLON tide gauge observations and used in
a recently developed data assimilation scheme for ADCIRC that corrects for unmodeled, low
frequency contributions to the total coastal water level. To account for missing tropical cyclone
energetics in the global meteorological reanalysis products, we will use a blending approach to
insert tropical cyclones into the background meteorology using ADCIRC’s Generalized
Asymmetric Holland Model on a moving, nested, high resolution grid. The ADCIRC-based
coastal water level reanalysis will form the basis for examining future water level statistics that
factor in sea level rise and future meteorological conditions. The water level reanalysis results
will be made publicly available on THREDDS Data Servers for access and dissemination to the
broader research community.