## 3 Results and Discussion
### Synthetic Wind Surge Epizodes  
In order to assess the impact of the potential increase in the speed of strong storm winds during extreme events that can be expected in the future on the increase in maximum water levels in the Elblag city area, five numerical simulations of synthetic storms were performed. In these hypothetical events, it was assumed that initially the water in the Vistula Lagoon would be in a hydrostatic state, with the water surface at 0 m above sea level. Then, the only factor forcing the water movement was the wind blowing from a constant NE direction and with a constant speed. The synthetic wind data were assumed to be 12, 20, 25, 30 and 35 ms\({}^{-1}\). The duration of the phenomenon was assumed to be equal to 48 h, which  
Figure 8: Scatter plots of observed vs. modeled water stage elevation at Nowakowo.  
Figure 9: Scatter plot of WSE at Nowakowo calculated with own model and HEC-RAS.  
resulted in the almost complete stabilization of the maximum water level in the lagoon in each of the calculation scenarios. All other physical and computational parameters were assumed as in the previously described simulation of the historical episode. The evolution of water stage elevation at Nowakowo gauging station for all five hypothetical scenarios is shown in Figure 10.  
The graph illustrates the changes in water level elevation at the southwest end of Vistula Lagoon, due to wind-driven water accumulation. The wind, coming from the north-east (NE), maintains a constant speed for 48 h, leading to a progressive rise in water levels. Higher wind speeds, particularly in the range of 30-35 ms\({}^{-1}\), result in more significant and rapid water level increases. The system approaches equilibrium after approximately 48 h, indicating the stabilization of storm surge effects. The response is non-linear, meaning that stronger winds lead to disproportionately higher water accumulation. This analysis highlights the potential impacts of storm surges under climate change conditions, demonstrating how increasing wind intensities could exacerbate coastal flooding risks in the future.  
The maximum water levels in the vicinity of Nowakowo for each scenario are presented in Table 2. The results indicate a significant flood hazard for Elblag due to wind-driven water accumulation in the Vistula Lagoon. In scenarios with wind speeds of 20 ms\({}^{-1}\) and higher, the warning level of 0.82 m asl and alarm level of 1.22 m asl are exceeded. With wind speeds of 25 ms\({}^{-1}\) or more, water levels reach or exceed 2 m, posing a severe threat of flooding along the Elblag River, which connects the city to the Vistula Lagoon. Such water levels could result in the overtopping of riverbanks, backflow into urban drainage systems, and increased inundation risks for low-lying areas of Elblag, Zulawy Elblaskie and Zulawy Wielkie. The trend highlights the growing flood hazard in the context of climate change, where more frequent and intense storms could lead to more severe storm surges. Measures such as reinforced flood defenses, improved drainage infrastructure, and early warning systems would be crucial to mitigating the impacts of these extreme events.  
\begin{table}
\begin{tabular}{l l l l l l} \hline \hline
**Speed of NE Wind (ms\({}^{-1}\))** & **12** & **20** & **25** & **30** & **35** \\ \hline Water stage elevation (m asl) & 0.55 & 1.40 & 2.19 & 3.12 & 3.69 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Water accumulation in the SW part of the Vistula Lagoon depending on the wind speed.  
Figure 10: Calculated water stage elevation at Nowakowo for synthetic wind scenarios.