*3.1. Wave Storm Concept and Definition*

Wave storm is a concept that is intuitively easy to understand but difficult to formally define. To a large extent, this is because a storm is a relative term referring to a period of time during which the severity of wave conditions is significantly intense with respect to the conditions normally observed at that location. In this context, wave storms represent extreme events with low frequency of occurrence but potentially severe impacts.

In terms of the above, there is no universally accepted procedure for the identification of wave storms. However, from a practical perspective, a wave storm is commonly considered a sequence of sea states with significant wave height exceeding a given threshold (*Ht*) for a specified minimum time period selected, known as the minimum storm duration (*Dmin*), so that when the duration (*D*) of an exceedance of *Hm0* is smaller than *Dmin*, the event is not considered a storm. In addition, it is assumed that two consecutive events must be considered a single storm if the significant wave height in the time between these events does not drop below *Ht* during a period larger than a certain minimum time interval, usually named the minimum inter-storm duration (*ISDmin*), where the time interval between the end of one storm and the beginning of the next is called the inter-storm period, or duration (*ISD*) (e.g., [17]). These parameters are schematically illustrated in Figure 3.

The above definition is not completely rigorous and free of drawbacks. The main problem is the selection of a threshold level that satisfies the criterion of independence of events and at the same time allows the identification of a sufficiently large number of events for the sample to be statistically representative. For this reason, there is great variability in criteria to establish this parameter, depending mainly on the geographic location and the local average wave climate [18].

**Figure 3.** Illustrative sketch of parameters used to define and select independent wave storms.
