Abstract
In the present work, a methodological framework, based on nonstationary extreme value analysis of nearshore sea-state parameters, is proposed for the identification of climate change impacts on coastal zone and port defense structures. The applications refer to the estimation of coastal hazards on characteristic Mediterranean microtidal littoral zones and the calculation of failure probabilities of typical rubble mound breakwaters in Greek ports. The proposed methodology hinges on the extraction of extreme wave characteristics and sea levels due to storm events affecting the coast, a nonstationary extreme value analysis of sea-state parameters and coastal responses using moving time windows, a fitting of parametric trends to nonstationary parameter estimates of the extreme value models, and an assessment of nonstationary failure probabilities on engineered port protection. The analysis includes estimation of extreme total water level (TWL) on several Greek coasts to approximate the projected coastal flooding hazard under climate change conditions in the 21st century. The TWL calculation considers the wave characteristics, sea level height due to storm surges, mean sea level (MSL) rise, and astronomical tidal ranges of the study areas. Moreover, the failure probabilities of a typical coastal defense structure are assessed for several failure mechanisms, considering variations in MSL, extreme wave climates, and storm surges in the vicinity of ports, within the framework of reliability analysis based on the nonstationary generalized extreme value (GEV) distribution. The methodology supports the investigation of future safety levels and possible periods of increased vulnerability of the studied structure to different ultimate limit states under extreme marine weather conditions associated with climate change, aiming at the development of appropriate upgrading solutions. The analysis suggests that the assumption of stationarity might underestimate the total failure probability of coastal structures under future extreme marine conditions.
Highlights
Variability of most likely 100-years total water level (TWL) estimates in all study areas exceeds 20% in the 21st century, while it increases to more than 35% when upper 95% confidence intervals are considered
Multivariate extreme sea states at selected areas of the Greek coastal zone, representing a possible realization of the future marine climate, are statistically treated via extreme value theory (EVT), considering nonstationarity on time scales longer than the seasonal or interannual scale, possibly attributed to climate change. They are combined with other sources of the coastal flooding hazard allowing for a robust derivation of extreme values, which is mainly focused on the associated response function of the TWL in coastal areas of the Aegean Sea
This hopefully allows for safer estimations of the coastal flooding hazards, more reliable design values for coastal protection works, and more efficient management of the coastal zone
Summary
The projected increase of future hydraulic loading conditions, combined with the limited residual service lifetime of many of the existing coastal defenses, creates an urgent need for a reliable estimation of future extreme sea conditions in nearshore areas, as well as of failure probabilities for port structures and harbor defenses under such extremes. This is a very important issue for integrated coastal zone management in the 21st century, as coastal areas worldwide are densely populated and assemble many significant economic activities
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