Escalating High Tide Flooding Along the Atlantic and Gulf Coast of the United States Due To Sea Level Rise

High tide flooding (HTF) occurs when astronomically driven water levels rise above flooding thresholds in coastal areas, which can happen on sunny days. In a warming climate, sea-level rise (SLR) is expected to change the frequency of HTF via a direct non-linear change in the mean water level. In this study, we investigate the impacts of SLR on HTF along the Gulf and Atlantic Coasts of the United States. We quantify the extent to which SLR is expected to exacerbate the HTF regime in the coming decades if no more flood protection is implemented. We estimate SLR at 10 km intervals using regression models, add it to numerically simulated tidal levels, and compare the results with estimated HTF thresholds. Our results provide continuous spatial coverage along the Atlantic and Gulf Coasts, showing a projected average rise of 0.35 ± 0.10 m in tidal levels above the mean higher high water (MHHW) by 2050, whereas Chesapeake Bay is projected to experience a greater rise of 0.39 ± 0.05 m, and Maine is expected to see a lower increase of 0.27 ± 0.08 m. This yields an increase of 10 days/year and 110 days/year in HTF hours in the years 2050 and 2100, respectively. Moreover, Pamlico Sound and Chesapeake Bay are expected to experience the most significant changes in HTF frequency, with more than 90 days of HTF by 2050s. Our results show that HTF regime in mesotidal semidiurnal systems are, on average, more sensitive to the projected SLR than the rest.