# Hydrological Analysis of Extreme Rain Events in a Medium-Sized Basin
## 3 Results
Specifically, the decrease was about 9.1% in the sub-basin W1460, having a reference value for wet conditions equal to 77, and about 15%, 10.1%, 4.9%, 24.7%, and 5% in the corresponding sub-basins W790, W800, W900, W1030 and W1020. Regarding the % imperviousness, the reference value of the sub-basin W900 fit better to verify the observed hydrograph. On the other hand, the applied value in the sub-basin W790 rose by 20%; in contrast, the calibrated values in the sub-basins W1460, W800, W1030, and W1020 were reduced by 18.8%, 15.8%, 30.1%, and 20.2%, respectively, in relation to the reference values. For the 26-30 June 2010 precipitation event, the Nash-Sutcliffe efficiency was very good for the sub-basins W1460 and W900, satisfactory for W790, good for W800 and W1030, whereas it was almost satisfactory for the sub-basin W1020. The particular coefficient was very good for the sub-basins W1460, W800, and W900 of the 22-25 June 2017 rain event, satisfactory for W790, and almost satisfactory for the sub-basins W1030 and W1020. As shown in Table 15, referring to the HBV-light hydrological model, the \(FC\) parameter followed the same trend as in the previous events of high precipitation intensity and double hydrological peak. Fewer differences were noticed in the calibrated parameters of the soil moisture routine at the W800 and W900 rural sub-basins with enough urbanized regions. Again, \(FC\) was distinctly greater in W800 than in W900. \(LP\) was similar in both sub-basins except the urban regions in which \(LP\) was slightly higher in W800. The \(BETA\) values were higher in W800 regarding the croplands and urban zones, but not in the forest areas in which the value was higher in W900. The \(BETA\) parameter was higher in the semi-urban sub-basin than in the urban one, mainly in cropland and urban areas, whereas in forest zones, \(BETA\) was the same in both sub-watersheds. The \(PERC\) rate was greater in most rural sub-basins and lower in the semi-urban and urban ones, except for the rural sub-basin W790 where it was particularly small. In the same sub-basin, especially small was also the \(UZL\) value. Concerning the rest of the sub-basins, the \(UZL\) value was greater in the W1460 and W1030, whereas it was smaller in the semi-urban and rural with quite urbanized regions sub-basins. The \(K0\) recession coefficient was notably higher and quite higher than \(KI\) and \(K2\) in the sub-basins W790 and W1030, respectively, displaying greater recession in the upper groundwater box. On the other hand, \(K0\) was particularly small in W1020. \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline
**Outlet of** & & & & _CN (III)_ & & **Initial** & & & **26–30 June** & **22–25 June** \\
**Sub-Basin** & & \(T_{c}^{B}\)**(h)** & \(\tau_{C}^{+R}\) & \(R\) **(h)** & **or CN** & **\%** & **Discharge** & **Pex Area** & **Constant** & **Ratio to** & **2010** & **2017** \\  & & & & & _CN (0)_ & & **(m3/s/km2)** & & & & **NSE** & **NSE** \\ \hline W1460 & 9.26 & 0.65 & 17.20 & 70 & 6.5 & 0.0125 & 0.8 & 0.35 & 0.810 & 0.897 \\ W790 & 8.08 & 0.575 & 10.94 & 68 & 12 & 0.001 & 0.8 & 0.275 & 0.570 & 0.613 \\ W800 & 14.15 & 0.575 & 19.14 & 71 & 16 & 0.005 & 0.8 & 0.275 & 0.722 & 0.869 \\ W900 & 11.77 & 0.525 & 13.01 & 77 & 16 & 0.0005 & 0.8 & 0.1 & 0.795 & 0.768 \\ W1030 & 2.82 & 0.15 & 0.50 & 61 & 51 & 0.0005 & 0.3 & 0.2 & 0.734 & 0.404 \\ W1020 & 18.04 & 0.425 & 13.34 & 66.5 & 33.5 & 0.0275 & 0.8 & 0.15 & 0.481 & 0.461 \\ \hline \hline \end{tabular}
\end{table} 
Table 14: HEC-HMS model verification via parameter calibration for the events of 26–30 June 2010 and 22–25 June 2017. The volume error index was also used in the calibration process of the aforementioned studied events per hydrological model, and is given by the following equation:  
\[diff(V)[\%]=\frac{V_{sim}-V_{obs}}{V_{obs}}\times 100\% \tag{7}\]  
where \(V_{sim}\) (m\({}^{3}\)) and \(V_{obs}\) (m\({}^{3}\)) are the total modeled and observed discharge volume, respectively.