# Hydrological Analysis of Extreme Rain Events in a Medium-Sized Basin
## 3 Results
The Nash-Sutcliffe index was also implemented on the HBV-light hydrological model. For the events of 28-30 May 2013 and 4-10 July 2013, that had high precipitation intensity, the detailed results of the Nash-Sutcliffe index per sub-basin and per hydrological model, due to the calibrated model parameters, are shown in Tables 9 and 10. As shown in Table 9, regarding the HEC-HMS hydrological model, for ratio \(R\)/(\(T_{c}\)+\(R\)), the selected values in relation to the reference values of Table 4 produced the following results: the ratio was risen by 2%, 4.6%, and 9.8% in the sub-basins W1460, W790 and W1030, respectively; on the other hand, it was decreased by 8.3%, 6.5% and 5.6% in the sub-basins W800, W900 and W1020. Concerning the _CN_ parameter, the chosen value after calibration was increased in the sub-basin W900 by 10%, while it was reduced by 10% in the sub-basins W1030 and W1020, after comparison to the reference values. In the rest of the sub-basins, the reference values of dry conditions were the ones that fit better to verify the observed hydrographs. Regarding the other parameter of the loss method, the % imperviousness of the sub-basins, except for the sub-basins W1030 and W1020 (in which there was the smallest difference with the reference values, specifically reduced by 9.5%), \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline
**Outlet of** & \(T_{c}\)**(b)** & \(\frac{R}{T_{c}\)**+\(R\)} & \(R\)**(b)** & \(\infty\)** & **Initial** & **Decsidering per Area (m\({}^{\circ}\)/s/km\({}^{\circ}\))** & **Recession** & **Ratio to** & **28-30 May 2013** & **4-10 July 2013** \\ \cline{1-1}
**Sub-Basin** & \(T_{c}\)**(b)** & \(\frac{R}{T_{c}\)**+\(R\)} & **R (b)** & **CN (b)** & **Impervious** & **Area** & **Con-** & **Ratio to** & **Nash-Sutcliffe** & **Existence** & **NSE** \\ \cline{1-1}
**W1460** & 14.07 & 0.65 & 26.13 & 38 & 11 & 0.005 & 0.8 & 0.475 & 0.604 & 0.919 \\
**W790** & 8.67 & 0.65 & 16.09 & 63 & 12 & 0.0035 & 0.8 & 0.1 & 0.569 & 0.858 \\
**W800** & 14.15 & 0.5 & 14.15 & 61 & 14 & 0.003 & 0.8 & 0.3 & 0.624 & 0.858 \\
**W900** & 11.77 & 0.525 & 13.01 & 70 & 42 & 0.001 & 0.8 & 0.1 & 0.774 & 0.781 \\
**W1030** & 4.03 & 0.125 & 0.58 & 73 & 66 & 0.012 & 0.3 & 0.1 & 0.843 & 0.765 \\
**W1020** & 18.04 & 0.35 & 9.72 & 63 & 38 & 0.01 & 0.8 & 0.025 & 0.713 & 0.897 \\ \hline \hline \end{tabular}
\end{table} 
Table 9: HEC-HMS (Hydrologic Engineering Center’s Hydrologic Modeling System) model verification via parameter calibration for the events of 28–30 May 2013 and 4–10 July 2013.  
in the rest of the sub-basins, the differentiation from the initial values was more noticeable in order to better verify the model. Indicatively, concerning the sub-basin W900, the modeled % imperviousness was high, which was explained by the fact that the sub-basin received an increased amount of precipitated water with very high intensity (25.2 mm/h), which caused the soil to saturate quickly and therefore the % imperviousness increased in relation to the reference value (16%). The efficiency of the Nash-Sutcliffe index ranged from satisfactory to very good for the sub-basins of the 28-30 May 2013 precipitation event, and for the 4-10 July 2013 severe rain event, it was very good for all the gauged sub-basins. According to Table 10, referring to the HBV-light hydrological model, the _FC_ parameter was higher in the rural sub-basins and significantly smaller in the urban and semi-urban sub-basins. As for the rural sub-basins with sufficiently urbanized regions, W800 and W900, differences were observed in the calibrated parameters of the soil moisture routine. In particular, W800 was better approached for high values of _FC_ and _BETA_, whereas low values of _LP_ were closer to its lower limit. On the contrary, the modeled hydrograph of W900 fitted better for lower values of _FC_ and _BETA_, and higher values of _LP_, closer to its higher potential limit.