## 2 Data and Methods
### Methods
#### 2.3.4 Assessment of Future Wave Energy Resource
Similarly as previously done for wind, the C\({}_{\text{mure}}\) index was calculated considering seven indices that evaluated the wave resource richness, variability, environmental risk, and cost parameters: wave energy resource (WP), downtime (DWNT), coefficient of variation index (\(C_{v}\)), monthly variability index (\(M_{\text{p}}\)), risk of extreme wave heights (Risk), water depth (WD), and distance to coast (DC). The richness of the wave resource parameter (WP) includes the potential wave energy resource available in the area under study, and is independent of the wave energy converter. Like for wind energy converters, wave converters also operate on a particular range of \(T_{p}\) and \(H_{s}\). In this context, and following [64], the DWNT index was defined with upper and lower thresholds set to \(H_{s}\) = 8 m and \(H_{s}\) = 1 m, which represent the level of \"power outages\" due to extreme wave conditions, and the time of calms, respectively. The temporal variability of the wave energy was also considered for the wave energy exploitation by means of the \(C_{v}\) and \(M_{\text{p}}\) indices that were calculated as for the wind resource, but changing the WPD for WP. Similar to EWS, a risk factor that takes into account extreme wave heights (EWH) was also considered. This index was calculated by means of the maximum \(H_{s}\) over a 50-year period, calculated based on the Gumbel curve method. The calculation of the cost factors (WD and DC) was performed for every grid pixel, using the same method applied for the wind resource, and the same normalization process described in Table 3.  
The other indices were also subjected to the same normalization process applied in the wind energy classification. The normalization criterion is described in Table 5.  
The weight coefficients for wave energy indices based on the Delphi classification method are described in Table 6. In particular, experts were selected from the steering committee and participants in the COST Action WECANet: A pan-European Network for Marine Renewable Energy ([[https://www.cost.eu/actions/CA17105/](https://www.cost.eu/actions/CA17105/)]([https://www.cost.eu/actions/CA17105/](https://www.cost.eu/actions/CA17105/))). As a first step, experts were questioned about the factors that they considered to be influential for wave energy converters. Experts were consulted only about general factors that did not depend on the particular features of a particular type of device. These factors, which include drivers that depend on the resource (mainly the amount of wave energy and its variability), on the environmental risk, and on cost constraints, were proposed and agreed \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Normalized** & **WP (kWm\({}^{-1}\))** & **DWNT (\%)** & \(C_{v}\) & \(M_{v}\) & **EWH (m)** \\ \hline
0/9 & \(<\)10 & \(<\)10 & \(>\)1.9 & \(>\)2.5 & \(>\)21 \\
1/9 & 10–20 & 10–20 & 1.7–0.9 & 2.25–2.5 & 20–21 \\
2/9 & 20–30 & 20–30 & 1.5–1.7 & 2.0–2.25 & 19–20 \\
3/9 & 30–40 & 30–40 & 1.3–1.5 & 1.75–2.0 & 18–19 \\
4/9 & 40–50 & 40–50 & 1.1–1.3 & 1.5–1.75 & 17–18 \\
5/9 & 50–60 & 50–60 & 0.9–1.1 & 1.25–1.5 & 16–17 \\
6/9 & 60–70 & 60–70 & 0.7–0.9 & 1.0–1.25 & 15–16 \\
7/9 & 70–80 & 70–80 & 0.5–0.7 & 0.75–1.0 & 14–15 \\
8/9 & 80–90 & 80–90 & 0.3–0.5 & 0.5–0.75 & 13–14 \\
9/9 & \(>\)90 & \(>\)90 & \(<\)0.3 & \(<\)0.5 & \(<\)13 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Normalization criterion used for wave energy resource (WP), DWNT, \(C_{v}\), \(M_{v}\), and extreme wave heights (EWH) indices related to richness factors, variability factors, environmental risk factors, and cost factors. by the experts. In a second step, a normalization method was adopted to compare different factors. Finally, in the last step, experts were consulted again to determine the weight of each factor following the protocol previously described. In this case, the indices that account for the wave resource richness are only two, compared to the three for the wind resource.