## 2 Materials and Methods
### Methodology
It should be noted that initial tests assuming a constant water surface elevation in the flooded polygons indicated that neglecting the slope of the water surface along the river leads to large errors. The flood depth map is obtained by subtracting the DEM from the flood surface elevation model (Figure 6b). Based on the flood depth map a fine tuning of the inundated areas delineation was also attempted. To this end, pixels with flood depth lower than 0.05 m were considered as not flooded. This threshold was used in order to avoid the characterization of pixels having very small differences between the land surface and the water surface as flooded areas, which may be the result of very small inaccuracies. The chosen threshold (0.05 m) is a round number and at the same time a reasonable amount that could be normally applied as irrigation water, so it is assumed that may not cause problems to the crops. In any case, other depth thresholds can be easily considered for specific purposes (e.g., for specific crops) based on the flood depth map. Additionally, the obtained flood surface elevation model was extended outside the boundaries of flooded polygons in order to further improve the inundated areas delineation by considering areas near the flooded polygons with lower ground elevation than the water elevation. As an additional step in this analysis, topographic depressions in the affected area were also identified based on the DEM. Topographic depressions are areas with lower ground elevation than their surrounding areas (local elevation minima) that have no direct connection to the downslope flow paths [78]. Accordingly, topographic depressions are susceptible to flooding in the absence of artificial drainage systems or in case that drainage systems cannot outflow the excessive water to the natural streams (e.g., due to high water levels). Normally, depressions are filled prior to hydrologic analyses requiring hydrologically connected flow networks [79]. However, in this analysis the topographic depressions are identified and analyzed as a means to assess areas prone to flooding. For this purpose, the method developed by [PERSON] and [PERSON] [78] was used to fill the topographic depressions in the affected area. In this approach, the presence of artificial drainage systems in the affected area was not considered. Then the original DEM was subtracted from the filled DEM in order to obtain the depth of the topographical depressions. The resulted output was classified with equal intervals to provide a measure of flood risk. Figure 6: Flood water depth calculation example. **(a)** Sampling points at the RS polygons boundaries; **(b)** flood water depth model. The obtained flood depth and flood risk raster datasets were clipped using the crop parcel polygons obtained by the Integrated Administration and Control System OPEKEPE [68]. This dataset contains detailed information on the exact boundaries and the crops cultivated in each farm and it is updated on a yearly basis [80]. It was thus made possible to assess in great detail the UAA affected as well the specific crops cultivated in the affected farms, neglecting for example uncultivable trails and ditches. Accordingly, the obtained results were able to provide a clearer picture of the flood impact and were directly comparable with the information provided by the Greek Agricultural Insurance Organization (ELGA) [81] on the compensations paid for this flood event.