## 4 Results  
Flood hazard probabilistic maps for Zamora city were derived from the MC analysis. The first time, the improved and extended maximum annual peak flow record for gs2121 gauge station at Zamora city was used for FFA by using GEV probability distribution with a Maximum Likelihood (ML) estimator for parameters (Figure 3b). This FFA gave us the GEV parameter values, which were used further in the MC analysis. The values of the GEV parameters were then used to transform the 500 series of probability values (according to a uniform distribution) into series of instantaneous maximum annual flow values. For each of these 500 series of peak flows, a GEV distribution function was fitted again to obtain the maximum instantaneous peak flow values associated with the different return periods considered in the study, as well as the confidence intervals of this estimated value. The results of the MC analysis for Zamora city are shown in Figure 3c and Table 1.  
Using the 500-year return period values as an example for flood hazard analysis, 2D hydrodynamic models were computed at the study site for the quantile value and some of the upper side confidence intervals (50%, 80%, 90%, and 99%). From hydrodynamic computing some flooding variables were defined as the flood-prone area, flow depth, and flow velocity. The results about flood-prone areas allow us to define the extension and probability of flooding areas in Zamora city, and at the same time, to identify the urban areas where, with a probabilistic confidence of 99%, there is an absence of flood hazards related to the 500-year return period. Figure 4 shows the probability map of flood-prone areas, where the left bank of the Douro River denotes a higher uncertainty due to its flatter shape. A clear example of this uncertainty is observed at the urban development of Zamora city on the left bank of the Douro River, which is partially affected by flooding when the quantile peak flow value is used but is fully affected when considering the 99% confidence interval. Flow depth and velocity are the main flood variables used to define hazards due to human loss of stability and direct economic damages. For the first one, the models proposed by [PERSON] et al. [5], and [PERSON] et al. [30] were computed for Zamora city, using both the quantile and confidence interval values. For the 500-year return period flood, both models show (Figure 5) a predominance of the highest hazard level, from the results associated with the hydrodynamic modelling of the quantile value associated with that return period (extending this maximum hazard zone as we consider the different confidence intervals). Differences between the two models considered can be observed, so the [PERSON] et al. [5] \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Return Period** & **Initial FFA** & **MC Analysis** & **50\% CI** & **67\% CI** & **80\% CI** & **90\% CI** & **95\% CI** & **99\% CI** \\ \hline T\({}_{2}\) & 595.3 & 609.1 & 615.1 & 617.7 & 620.4 & 623.7 & 626.4 & 631.9 \\ T\({}_{5}\) & 1016.3 & 1040.8 & 1064.0 & 1074.2 & 1084.8 & 1097.3 & 1108.1 & 1129.2 \\ T\({}_{10}\) & 1351.7 & 1375.1 & 1410.7 & 1426.5 & 1442.7 & 1461.9 & 1478.6 & 1511.0 \\ T\({}_{25}\) & 1840.0 & 1862.9 & 1930.9 & 1961.1 & 1992.2 & 2028.8 & 2060.6 & 2122.6 \\ T\({}_{50}\) & 2255.4 & 2279.2 & 2379.9 & 2424.7 & 2470.6 & 2524.8 & 2571.9 & 2663.7 \\ T\({}_{100}\) & 2718.9 & 2745.4 & 2898.1 & 2965.9 & 3035.4 & 3117.6 & 3189.0 & 3328.1 \\ T\({}_{200}\) & 3245.1 & 3269.6 & 3533.5 & 3650.8 & 3771.1 & 3913.3 & 4036.6 & 4277.3 \\ T\({}_{500}\) & 4020.4 & 4066.1 & 4437.6 & 4602.6 & 4771.9 & 4972.0 & 5145.6 & 5484.3 \\ T\({}_{1000}\) & 4696.8 & 4759.5 & 5288.9 & 5524.0 & 5765.3 & 6050.4 & 6297.7 & 6780.4 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: T\({}_{\text{year}}\) peak flow values (m\({}^{3}\) s\({}^{-1}\)) from initial FFA and further MC analysis (including upper confidence intervals—CI) in Zamora city. model shows a greater extension of mid-hazard levels than the [PERSON] et al. (2020) model.