Assessment of water levels from 43 years of NOAA's Coastal Ocean Reanalysis (CORA) for the Gulf of Mexico and East Coasts Provisionally Accepted

Linta Rose^1* Matthew J. Widlansky^1* Xue Feng¹ Philip Thompson² Taylor G. Asher³ Gregory Dusek⁴ Brian Blanton⁵ Richard A. Luettich³ John Callahan^{4, 6} William Brooks⁴ Analise Keeney⁴ Jana Haddad^{4, 6} William Sweet⁴ Ayesha Genz⁷ Paige Hovenga⁸ John Marra⁷ Jeffrey Tilson⁵

• ¹Cooperative Institute for Marine and Atmospheric Research, University of Hawaii at Manoa, United States
• ²Department of Oceanography, School of Ocean and Earth Science and Technology, University of Hawaii at Manoa, United States
• ³Coastal Resilience Center, University of North Carolina at Chapel Hill, United States
• ⁴National Ocean Service (NOAA), United States
• ⁵Renaissance Computing Institute, United States
• ⁶Ocean Associates, Inc., United States
• ⁷National Centers for Environmental Information, NOAA, United States
• ⁸NOAA Physical Sciences Laboratory, United States

Coastal water level information is crucial for understanding flood occurrences and changing risks. Here, we validate the preliminary version (0.9) of NOAA's Coastal Ocean Reanalysis (CORA), which is a 43-year reanalysis of hourly coastal water levels for the Gulf of Mexico and Atlantic Ocean (i.e., the Gulf and East Coast region, or GEC). CORA-GEC v0.9 was conducted by the Renaissance Computing Institute using the coupled ADCIRC+SWAN coastal circulation and wave model. The model uses an unstructured mesh of nodes with varying spatial resolution that averages 400 m near the coast and is much coarser in the open ocean. Water level variations associated with tides and meteorological forcing are explicitly modeled, while lower-frequency water level variations are included by dynamically assimilating observations from NOAA's National Water Level Observation Network. We compare CORA to water level observations that were either assimilated or not, and find that the reanalysis generally performs better than a state-of-the-art global ocean reanalysis (GLORYS12) in capturing the variability on monthly, seasonal, and interannual timescales as well as the long-term trend. The variability of hourly non-tidal residuals is also shown to be well resolved in CORA when compared to water level observations. Lastly, we present a case study of extreme water levels and coastal inundations around Miami, Florida to demonstrate an application of CORA for studying flood risks. Our assessment suggests that NOAA's CORA-GEC v0.9 provides valuable information on water levels and flooding occurrence from 1979-2021 in areas that are experiencing changes across multiple time scales. CORA potentially can enhance flood risk assessment along parts of the U.S. Coast that do not have historical water level observations.