DEcadal predictability of coastal exTremE sea levels under ClimaTe change

[Cod. PID2021-124085OB-I00 DETECT]

Coastal areas are among the most exposed and vulnerable regions to natural hazards and, in particular, those related to sea-level rise and storminess represent a serious and increasing threat of human-induced climate change. The greatest coastal impacts are expected to be caused by extreme episodes. Coastal extreme sea levels (CESL) arise from the interplay between mean sea-level changes, tides, atmospheric pressure and surface winds. Despite temporal variability in CESL being largely driven by mean sea-level changes, it has been shown that CESL unrelated to mean sea level display substantial temporal variability at interannual, decadal and longer time scales. DETECT project focuses on CESL changes (in both mean and variability) along the European (Atlantic and Mediterranean) coasts that are
linked to storminess at decadal and multi-decadal time scales. The project uses simulated atmospheric mean sea level pressure and surface wind fields from atmospheric reanalyses and from a large ensemble of initialised decadal runs of coupled atmosphere-ocean models. Since these models do not provide sea level as a diagnosis variable, a combination of hydrodynamic and statistical approaches, together with in-situ high-frequency sea-level observations from tide gauges, is used to infer CESL time series at the coastal regions. Based on this large ensemble of extreme data, DETECT aims at quantifying decadal variations in CESL along the European coasts since 1960. Relying on the
fact that there are predictable components of the climate system, especially for the winter regional climate of the North Atlantic, the final goal is to understand, and eventually disentangle, the natural variability from the climate-induced forced signal in CESL and to ultimately predict their behaviour in the forthcoming years. DETECT addresses the questions on whether there have been shifts in the probability distribution of CESL during the most recent decades in Europe and whether these changes can be linked to an external forcing. The responses to these questions are explored using a complete suite of extreme value theory approaches for non-stationary processes. In addition, initialised decadal forecasts are used to determine the time horizons for which the changes in the probability distribution of CESL can be anticipated along different European coastal regions. The project capitalises on the synergies of a team with experts in ocean sciences and sea level variability, atmospheric sciences and statistical methods to improve the current knowledge on the mechanisms of changes of CESL and their relationship with climate change.