Ocean Science www.ocean-sci.net 1812-0784 1812-0792 6 2 2010 10.5194/os-6-525-2010 http://www.ocean-sci.net/6/525/2010/ http://www.ocean-sci.net/6/525/2010/os-6-525-2010.html http://www.ocean-sci.net/6/525/2010/os-6-525-2010.pdf 525 538 2010-06-04 Statistical trend analysis and extreme distribution of significant wave height from 1958 to 1999 – an application to the Italian Seas G. Martucci S. Carniel sandro.carniel@ismar.cnr.it J. Chiggiato M. Sclavo P. Lionello M. B. Galati Consorzio Venezia Ricerche, Marghera, Venice, Italy CNR-ISMAR, Castello 1364/A, 30122 Venice, Italy University of Lecce, Department of Material Sciences, Via Arnesano, 73100 Lecce, Italy now at: School of Physics, and Centre for Climate and Air Pollution Studies, Environmental Change Institute, National University of Ireland, Galway, Ireland The study is a statistical analysis of sea states timeseries derived using the wave model WAM forced by the ERA-40 dataset in selected areas near the Italian coasts. For the period 1 January 1958 to 31 December 1999 the analysis yields: (i) the existence of a negative trend in the annual- and winter-averaged sea state heights; (ii) the existence of a turning-point in late 80's in the annual-averaged trend of sea state heights at a site in the Northern Adriatic Sea; (iii) the overall absence of a significant trend in the annual-averaged mean durations of sea states over thresholds; (iv) the assessment of the extreme values on a time-scale of thousand years. The analysis uses two methods to obtain samples of extremes from the independent sea states: the <i>r-largest annual maxima</i> and the <i>peak-over-threshold</i>. The two methods show statistical differences in retrieving the return values and more generally in describing the significant wave field. The <i>r-largest annual maxima</i> method provides more reliable predictions of the extreme values especially for small return periods (&lt;100 years). 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