Global assessment of coastal storm hazards on coastal barriers in a changing climate using process-based indicators

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Improved estimates of extreme wave conditions in coastal areas from calibrated global reanalyses

Publication . Fanti, Valeria; Ferreira, Oscar; Kümmerer, Vincent; Loureiro, Carlos

The analysis of extreme wave conditions is crucial for understanding and mitigating coastal hazards. As global wave reanalyses allow to extend the evaluation of wave conditions to periods and locations not covered by in-situ measurements, their direct use is common. However, in coastal areas, the accuracy of global reanalyses is lower, particularly for extreme waves. Here we compare two leading global wave reanalyses against 326 coastal buoys, demonstrating that both reanalyses consistently underestimate significant wave height, 50-year return period and mean wave period in most coastal locations around the world. Different calibration methods applied to improve the modelled extreme waves, resulting in a 53% reduction in the underestimation of extreme wave heights. Importantly, the 50-year return period for significant wave height is improved on average by 55%. Extreme wave statistics determined for coastal areas directly from global wave reanalyses require careful consideration, with calibration largely reducing uncertainty and improving confidence. Leading global wave reanalyses greatly underestimate extreme wave heights in coastal regions but this can be reduced with the use of individual or global calibration equations, according to an evaluation of wave height reanalyses validated against data from 326 coastal buoys.

2023Journal article

Open access

Global assessment of coastal storm hazards on Barrier islands

Publication . Fanti, Valeria; Ferreira, Óscar; Loureiro, Carlos

The vulnerability of barrier islands to coastal storm hazards is a growing challenge, exacerbated by climate change. Local high-resolution information on storm forcing and geomorphology has allowed the development of early warning systems to predict hazards and implement preparedness strategies. However, collecting high-resolution pre- and post-storm data can be costly, challenging and unfeasible at many coastal locations. The use of global low-resolution topo-bathymetry and wave reanalysis datasets presents an unprecedented opportunity to expand coastal hazard assessments, even if at the cost of introducing errors and uncertainties. Aiming to evaluate the response of wave-dominated barrier islands to extreme storms at a global scale, this study validated the latest global wave reanalyses and digital elevation models against high resolution data. The validation confirmed biases associated with the resolution of global datasets and their inability to resolve complex features of wave propagation and morphology at local scales. Underestimation of extreme wave conditions in coastal areas was observed, and calibration equations were developed to reduce this negative bias. For the topo-bathymetry of barrier islands, an underestimation of the dune crest was identified, and gaps at the land-ocean interface were filled by merging the topo-bathymetry datasets using an equilibrium profile. The best performing global datasets were selected for the first global assessment of erosion and flooding hazards of natural barrier islands. This was achieved simulating the impact of a coastal storm with 50-year return period wave heights using the XBeach process-based model. Based on the implementation of process-based indicators, the strong control that storm hydrodynamics exert on the erosional response was highlighted, allowing the identification of erosion and flooding hotspots that coincided with areas of extra-tropical and tropical cyclone impact. These findings highlight the global patterns of barrier island vulnerability and provide a framework for prioritizing risk mitigation efforts in the face of intensifying coastal hazards.

2025-06-05Doctoral thesis

Open access