Long-duration storm surges due to 2023 successive UK storms Ciarán and Domingos: Generation, field surveys, and numerical modelling

We model the long-duration storm surges generated by October–November 2023 storm chain in the English Channel employing a hybrid method including numerical modelling, field surveys and analysis of oceanic and atmospheric data. The event consisted of three successive storms: a weaker unnamed storm (27–30 October), Storm Ciarán (2–3 November with minimum pressure 948 hPa) and Storm Domingos (4–5 November with minimum pressure 958 hPa). The average surge duration produced by this storm chain was 10.5 days. The average maximum air pressure drop was 42 hPa during Ciarán and 23 hPa during Domingos. These pressure drops, combined with onshore wind stresses, led to average maximum storm surge amplitudes of 92 cm for Ciarán and 74 cm for Domingos. We accurately modelled storm surges using a three-level nested grid system and validated the results with tide gauge data. Sensitivity analysis showed a spatially-dependant impacts from tides and waves on maximum surge amplitudes. To correlate our modelling and data analysis with actual conditions on the ground, field surveys were conducted where we measured a runup heights of 4.1 m in Chesil Beach and 2.1 m in West Bay. These values were successfully reproduced by two independent empirical runup models enabling adaption of suitable models for storm hazard mitigation and resilience. A meteotsunami with an amplitude of 17–23 cm and a period of 11–40 min was identified during Ciarán. The innovative hybrid framework developed in this study is recommended for building robust systems for storm warnings and coastal resilience.