## 6 Conclusions  
This study utilized the FFISS with four categories (encompassing the built environment, natural environment, mobile objects, and population) with 10 severity classes to evaluate two flood events occurring in 2009 and 2020 within the same catchment area. The data collection and analysis were conducted using advanced technology, including drones for capturing high-resolution videos and photographs of extensive portions of the affected area, complemented by ground-based observations. The application of the FFISS enabled a comprehensive comparison of the severity of the two events, yielding reliable results for both the highest and lowest severity classes and identifying areas with the most significant impacts. The findings reveal that the severity scale for both flood events ranged from Classes II to VIII. However, the 2009 flood exhibited higher severity classes near the delta of the Lilas River, while the 2020 flood affected a broader spectrum of areas, including locations near the Vassiliko bridge, upstream regions, and areas extending toward Pissonas. Notably, the 2020 flood was of greater intensity, characterized by higher flow velocities, increased discharge, and elevated water levels, compared to the 2009 flood. Consequently, more pronounced phenomena were observed, such as sediment deposition in the Lilas River bed, bank erosion, bridge collapses, and the displacement of mobile objects--impacts of high severity that were not present during the 2009 flood. It is also critical to highlight that in 2009, the widening of the riverbed near its delta substantially affected the built environment, destroying buildings. This increased the severity classification for the built environment, as the absence of these structures in 2020 precluded further impacts. Regarding the practical application of the severity scale, it demonstrated utility even in scenarios where georeferenced impact data were unavailable, as evidenced in the case of the 2009 flood for the movable objects and population sectors. Based on the available information, it is inferred that the severity classes for these sectors did not exceed Class IV, thereby not altering the overall severity profile for all the sectors in 2009. By contrast, the 2020 flood witnessed the displacement of large vehicles, including trucks and bulldozers, and fatalities, reflecting the heightened risks associated with increased discharge. Through the application of the FFISS, it is observed that the maximum severity in 2020 has decreased in proximity to the delta of the Lilas River. This phenomenon is likely attributed to the widening of the streambed, which led to a reduction in water levels and a diminished presence of water within the floodplain. This hypothesis is consistent with the findings from previous studies that have examined risk mitigation strategies in the aftermath of flooding events [63]. In addition, the current infrastructure and condition of the riverbed are inadequate to withstand high-intensity hydrometeorological events. Consequently, the widening and delineation of the riverbed are essential to accommodate increased water flow, alongside the construction of appropriate artificial hydraulic structures. Furthermore, upstream areas require the implementation of suitable retention measures to mitigate water velocity and regulate downstream flow. Lastly, it is demonstrated that targeted artificial interventions are highly desirable to effectively reduce the flood risk. The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app15031100/s1](https://www.mdpi.com/article/10.3390/app15031100/s1)]([https://www.mdpi.com/article/10.3390/app15031100/s1](https://www.mdpi.com/article/10.3390/app15031100/s1)). File S1: Comprehensive overview of the scale's categories and the corresponding severity classes of impacts resulting from flood events [18]. **Author Contributions:** Conceptualization, N.I.S. and M.D. ; methodology, M.D., G.D., Z.A., M.M., K.-N.K., E.A., N.I.S. and M.G. ; software, N.I.S., M.D. and S.M.