Unprecedented storm surges across European coastlines

Recent research has considerably advanced our ability to model extreme storm surges. Nevertheless, simulating unprecedented events remains a challenge. Current large-scale storm surge studies often rely on conventional statistical approaches to extrapolate data beyond historical records. However, these approaches entail large uncertainties and lack the capacity to physically characterise individual events. Furthermore, research on unprecedented events primarily focuses on hazard magnitude, often overlooking other dimensions relevant for risk management decisions.This study addresses these gaps by examining unprecedented storm surges at a European scale across multiple dimensions. We follow a large-ensemble approach to generate numerous alternative pathways of reality, capturing a broader range of climate variability than the observational records. By pooling ensembles from the ECMWF SEAS5 seasonal forecast and forcing the Global Tide and Surge Model (GTSM), we obtain a 525-year dataset of unbiased, independent storm surge events. This synthetic dataset enables the identification of physically plausible events beyond those found in historical records. We evaluate the dataset against reanalysis-based storm surges to uncover and characterise unprecedented events across three dimensions: magnitude, spatial extent and temporal occurrence. Understanding these different dimensions of unprecedence provides a significant advance in our knowledge of coastal flood risk in Europe and supports improved coastal flood risk management decisions.