Detection and quantification of trends in time series of significant wave heights: An application in the Mediterranean Sea

The analysis of long-term trends in time series of wave parameters has an high engineering relevance. These trends may affect the estimates of parameters with high return period that are used for the design of several engineering projects. This work analyses the use of linear regressions for detecting and quantifying long-term trends in time series of data. In particular, the reliability of a linear trend slope, modified in order to minimize the weight of possible outliers, is evaluated. To this end, this slope is compared against the outcomes of two methods that do not imply the hypothesis of linear trend: the Mann–Kendall test and the Innovative Trend Analysis. An application to significant wave height time series over the Mediterranean Sea is presented. Time series of 40 years of numerical hindcast of sea states over the whole basin were analysed, and the methods taken into account were applied to the annual maxima, the annual 98th percentile and the annual mean significant wave height. The results show that the use of the investigated linear slope is meaningful, therefore this was used to assess the spatial distribution of trends in the Mediterranean Sea. Results are presented and discussed for all the statistics investigated.