Storm processes and impacts in geologically controlled barrier islands

Funder

Organizational Unit

Publications

Storm identification for high-energy wave climates as a tool to improve long-term analysis

Publication . Kümmerer, Vincent; Ferreira, Óscar; Fanti, Valeria; Loureiro, C.

Coastal storms can cause erosion and flooding of coastal areas, often accompanied by significant social-economic disruption. As such, storm characterisation is crucial for an improved understanding of storm impacts and thus for coastal management. However, storm definitions are commonly different between authors, and storm thresholds are often selected arbitrarily, with the statistical and meteorological independence between storm events frequently being neglected. In this work, a storm identification algorithm based on statistically defined criteria was developed to identify independent storms in time series of significant wave height for high wave energy environments. This approach proposes a minimum duration between storms determined using the extremal index. The performance of the storm identification algorithm was tested against the commonly used peak-over-threshold. Both approaches were applied to 40 and 70-year-long calibrated wave reanalyses datasets for Western Scotland, where the intense and rapid succession of extratropical storms during the winter makes the identification of independent storm events notably challenging. The storm identification algorithm provides results that are consistent with regional meteorological processes and timescales, allowing to separate independent storms during periods of rapid storm succession, enabling an objective and robust storm characterisation. Identifying storms and their characteristics using the proposed algorithm allowed to determine a statistically significant increasing long-term trend in storm duration, which contributes to the increase in storm wave power in the west of Scotland. The coastal storm identification algorithm is found to be particularly suitable for high-energy, storm-dominated coastal environments, such as those located along the main global extratropical storm tracks.

2023-12Journal article

Open access

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

Distinct shoreline behaviour along storm‐dominated and geologically controlled coastal barriers

Publication . Kümmerer, Vincent; Ferreira, Óscar; Loureiro, Carlos

Contemporary shoreline change is driven by a complex combination of factors, and as such is often highly variable along the coast. While differences in beach morphology can explain some of the variability in shoreline change, the geological constraints imposed by coastal geology are often overlooked. This work examines the influence of foreshore configurations with varying degrees of non-dynamic geological control, which are analysed in combination with hydrodynamic forcing to investigate seasonal to multiannual shoreline evolution along five coastal barriers in the Outer Hebrides, Western Scotland. These barriers are characterised by strongly geologically constrained evolution and are exposed to a storm-dominated wave climate. Due to the variable temporal interval between available cloud-free Planet Scope images, monthly averaged vegetation lines from 2016 to 2023 were derived from satellite imagery as a shoreline position indicator using an automated approach validated by visual inspection. The satellite-derived vegetation lines have a sub-pixel accuracy with a root mean square error of 3 m. Changes in monthly averaged shoreline position are statistically correlated with monthly extreme storm conditions, characterised by both extreme water levels and wave conditions. However, the control exerted by the variable geological configuration along the barriers results in distinct inter- and intra-site shoreline change behaviour, with lower shoreline variability observed in barrier sectors fronted by rocky foreshores, compared to sediment-rich foreshores. The observed multiannual shoreline change from 2016 to 2023 is characterised by a small but statistically significant accreting trend (mean 0.4 m/yr), likely representing the recovery of the barriers from extreme winter storms that impacted northern European coasts from 2013 to 2015. The results demonstrate that considering variable geological controls in shoreline change assessments improves the understanding of shoreline variability along coastal barriers, allowing to identify distinct storm-driven shoreline behaviour according to the degree of geological control.

2025-03-25Journal article

Restricted access