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

   https://doi.org/10.1029/2024EF005328  

   Mahmoudi, Sadaf; Moftakhari, Hamed; Muñoz, David F; Radfar, Soheil; Sweet, William; Moradkhani, Hamid (September 2025, Earth's Future)

   Abstract 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. 

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2. Profound Changes in the Seasonal Cycle of Sea Level Along the United States Mid‐Atlantic Coast

   https://doi.org/10.1029/2024GL112273  

   Yang, Jiayan; Chen, Ke (January 2025, Geophysical Research Letters)

   Abstract The monthly mean sea level along the U.S. Mid‐Atlantic Coast varies seasonally, reaching a minimum in January and a maximum in September during the 1960–2020 period. However, this seasonal cycle has changed significantly on multi‐decadal timescales. In the last two decades, the annual minimum has shifted from January to February. The amplitude of seasonal changes increased by 65% from 14.16 cm in 1980–1999 to 23.16 cm in 2000–2020. Even more concerning, the maximum sea level in September rose by 82%, from 6.81 to 12.38 cm, potentially exacerbating coastal flooding over the past 20 years. A two‐layer ocean model effectively replicates both the phase and magnitude of the observed changes and attributes these shifts to changes in wind stress near the coast, with relatively minor influence from deep ocean forcing. Both alongshore and cross‐shore wind stress changes are found to contribute to changes in the sea level's seasonal cycle. 

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3. The Influence of Future Changes in Tidal Range, Storm Surge, and Mean Sea Level on the Emergence of Chronic Flooding

   https://doi.org/10.1029/2023EF003993  

   Hague, Ben S; Talke, Stefan A (February 2024, Earth's Future)

   Abstract Sea‐level rise is leading to increasingly frequent coastal floods globally. Recent research shows that changes in tidal properties and storm surge magnitudes can further exacerbate sea‐level rise‐related increases in flood frequencies. However, such non‐stationarity in tide and storm surge statistics are largely neglected in existing coastal flood projection methodologies. Here we develop a framework to explore the effect that different realizations of various sources of uncertainty have on projections of coastal flood frequencies, including changes in tidal range and storminess. Our projection methodology captures how observed flood rates depend on how storm surges coincide with tidal extremes. We show that higher flood rates and earlier emergence of chronic flooding are associated with larger sea‐level rise rates, lower flood thresholds, and increases in tidal range and skew surge magnitudes. Smaller sea‐level rise rates, higher flood thresholds and decreases in sea level variability lead to commensurately lower flood rates. Percentagewise, changes in tidal amplitudes generally have a much larger impact on flood frequencies than equivalent percentagewise changes in storm surge magnitudes. We explore several implications of these findings. Firstly, understanding future local changes in storm surges and tides is required to fully quantify future flood hazards. Secondly, existing hazard assessments may underestimate future flood rates as changes in tides are not considered. Finally, identifying the flood frequencies and severities relevant to local coastal managers is imperative to develop useable and policy‐relevant projections for decisionmakers. 

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4. Quantifying Historic Storm Surge and Risk Reduction Costs: A Case Study for Lafitte, Louisiana

   https://doi.org/10.1007/s10584-019-02636-x  

   Siverd, C.G. (January 2020, Climatic change)

   Rising sea levels have increased flood risk in coastal communities on both the east and west coasts of the USA. The goal of this analysis is to approximate flood defense costs from cyclonic flooding as a partial means to evaluate the resilience of coastal communities. Storm surge models were previously constructed via an established approach to represent historical and future coastal Louisiana landscapes and associated flood patterns. Coastal flooding was also previously simulated via a suite of 14 hurricanes. Approximate levee heights surrounding Lafitte, Louisiana, are calculated from the surge and wave output of Hurricane Isaac, the predominated hurricane in the Lafitte area for all years examined (NAVD88, m): 1.68 (1930), 2.92 (1970), 3.30 (1990), 4.82 (2010), 5.93 (2030), 6.57 (2050), 7.16 (2070), 7.70 (2090), and 8.22 (2110). Approximate costs per person are also calculated (2010 USD): $49,500 (1930), $41,400 (1970), $37,500 (1990), $181,600 (2010), $223,600 (2030), $247,800 (2050), $269,900 (2070), $290,100 (2090), and $309,800 (2110). The Gulf of Mexico (GOM) migrated 7.4 km inland within the Louisiana Barataria coastal basin between 1973 and 2010. For each person in Lafitte, flood defense costs increased approximately (2010 USD) $19,000 per person per kilometer inland migration of the GOM from 1973 to 2010. The methodology developed in this case study effectively connects wetland loss with increased flood defense costs and can be applied to communities with similar challenges. 

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5. Atlantic meridional overturning circulation increases flood risk along the United States southeast coast

   https://doi.org/10.1038/s41467-023-40848-z  

   Volkov, Denis L.; Zhang, Kate; Johns, William E.; Willis, Joshua K.; Hobbs, Will; Goes, Marlos; Zhang, Hong; Menemenlis, Dimitris (December 2023, Nature Communications)

   Abstract The system of oceanic flows constituting the Atlantic Meridional Overturning Circulation (AMOC) moves heat and other properties to the subpolar North Atlantic, controlling regional climate, weather, sea levels, and ecosystems. Climate models suggest a potential AMOC slowdown towards the end of this century due to anthropogenic forcing, accelerating coastal sea level rise along the western boundary and dramatically increasing flood risk. While direct observations of the AMOC are still too short to infer long-term trends, we show here that the AMOC-induced changes in gyre-scale heat content, superimposed on the global mean sea level rise, are already influencing the frequency of floods along the United States southeastern seaboard. We find that ocean heat convergence, being the primary driver for interannual sea level changes in the subtropical North Atlantic, has led to an exceptional gyre-scale warming and associated dynamic sea level rise since 2010, accounting for 30-50% of flood days in 2015-2020. 

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