Italian seas wave extremes: a preliminary assessment

Occasional damages occurring to offshore structures and routing ships have brought attention on whether conventional analyses of stormy seas are adequate to represent wave extremes. Indeed, field and laboratory data showed that in short-crested seas (typical of stormy conditions) the maximum wave elevation is rarely retrieved by a single-point observation (a buoy, for example), which tends to underestimate the actual extreme that occurs over an area surrounding the point. Recently, stochastic models for the prediction of maxima of multidimensional Gaussian random fields (e.g. the Piterbarg's theorem and the Adler and Taylor's Euler Characteristics approach) have been successfully applied to ocean wave statistics, thus permitting to extend the extreme value analysis from the time to the space-time domain. Results from space-time models are here firstly compared to observations gathered by an optical stereo system, and then used to preliminarily assess wave extremes over the Italian Seas, by using a numerical model analysis covering the period 2007-2013. In particular, space-time maxima are estimated as affecting a fishing boat and a cruise ship, showing that, locally, space-time extremes may exceed time-based values up to about 50 %.