## 3 Results and Discussion  
Model system simulations have been performed for the entire year 2017. The emphasis was given to the analysis of the high, but not extreme, wintertime conditions, where wintertime was considered the six-month period from January to March and from October to December. The wind fields considered are those provided by the US National Centres for Environmental Prediction (NCEP). The spatial resolution of the wind data is 0.325 degrees in both latitude and longitude while the temporal resolution is 3 h.  
Some of the most relevant results of the simulations performed with the SWAN model for the year 2017 are analyzed and discussed next. These consider the eight computational domains (corresponding to four different levels) defined before. Also, for each domain the physical parameterizations presented in Table 4 have been activated in the model setting. The discussion focuses on the high wave energy conditions. From this perspective, Figure 4 illustrates high wave conditions in the entire basin of the Black Sea (computational domain Sph1). These model results correspond to the time frame 8 January 2017. Figure 4a presents the significant wave height scalar fields (_H_s) and the wave vectors and Figure 4b the wave power scalar fields (_P_w) and the energy transport vectors. The maximum values of the significant wave height and wave power are also indicated, they are: _Hsmax_ = 5.2 m and _Pwmax_ = 70 kW/m. These correspond to two different locations offshore the Danube Delta, which are very close. At this point, it has to be highlighted that the case study presented in Figure 4 corresponds to one of the most common patterns concerning the spatial distribution of the wave energy in the basin of the Black Sea. Figure 3: _H_s scatter diagrams: **a)** SWAN without DA and **b)** SWAN with DA (**right**), results corresponding to the 15-year time interval 1999–2013. According to this pattern, the tendency of the wave energy is to concentrate in the western part of the basin in the Black Sea. This is also related to the characteristics of the atmospheric circulation, according to which the strongest winds blowing over the Black Sea are usually from the northeast. Going to the second level (corresponding to the spherical computational domain Sph2), Figure 5 presents high, but not extreme, wave conditions in the western Black Sea. The model results correspond in this case to the time frame 4 February 2017. Figure 5a illustrates the significant wave height scalar fields and wave vectors while Figure 5b the wave power scalar fields and energy transport vectors. The maximum values of the significant wave height and wave power are _Hsmax_ = 4.9 m and _Pwmax_ = 57 kW/m. As shown in the figure, these maximums are located in two different points, both close the eastern boundary approximately in the center of the computational domain. Figure 4: High wave conditions in the Black Sea (computational domain Sph1), model results corresponding to the time frame 8 January 2017. **(a)** Significant wave height scalar fields and wave vectors (represented by black arrows); **(b)** wave power scalar fields and energy transport vectors (represented by red arrows). The maximum values of the significant wave height and wave power are also indicated. Regarding now level 3, Figure 6 presents high wave conditions at the mouths of the Danube River (computational domain Sph3). The model results correspond to the time frame 22 March 2017. Figure 6a illustrates the significant wave height scalar fields and wave vectors while Figure 6b the wave power scalar fields and energy transport vectors. The maximum values of the significant wave height and wave power are _Hsmax_ = 5.2 m and _Pwmax_ = 58 kW/m. Although they are both located in the southern side of the domain, their positions are different this time. Thus, the significant wave height has the highest value at the mouth of the Saint George arm while the point with the maximum wave power is located about 0.35 degrees offshore, close to the southern boundary of the SWAN domain.