## 4 Results
### Resolution Effects of the Grid Cell Size with Fixed Parameter Sets  
Figure 8 shows the hydrographs in the Dongkok watershed, which varied depending on the grid cell size with fixed input parameter sets. Fixed parameter sets were used to investigate the resolution effects of the grid cell size. This study chose a fixed parameter set that displayed the best fit in a 5 m grid cell size based on the Rainfall-runoff events in Table 4. Figure 8 shows that the estimated hydrographs with a smaller grid cell size were closer to the observed hydrograph. In contrast, when the grid cell size was larger, the simulated hydrograph was larger than the observed one because the grid cell size and contributing area were larger. The larger contributing area resulted in more runoffs. In particular, Figure 8b,d show that the peak rainfall matched with the estimated peak hydrographs under different grid cell sizes, which indicated that the larger the grid cell size, the larger the contributing area and the more sensitive the runoff to peak rainfall. Figure 9 shows the hydrographs whose DEM grid size varied with the application of fixed parameter sets in each hydrological event in the leemokjung watershed. Similarly, the input parameter set used the best fitting parameter set for the 5-m grid size in Table 5. Similar to the Dongkok watershed, the estimated runoffs well matched with the observed hydrographs because the DEM grid size was smaller in the leemokjung watershed. In Figures 8 and 9, the hydrographs for coarser DEM resolution provided greater surface runoffs. It is because the depth \(z_{i}\) of the groundwater decreases as the topographic index increases, from Equation (6) [16; 35]. Particularly, negative \(z_{i}\) means the unsaturated zone in the DEM grid is saturated. Decreasing depth of the groundwater leads to decreasing infiltration rate and increasing surface runoff in the constant rainfall condition. In other words, the infiltration rate decreases as a topographic index increases or the DEM grid cell resolution is coarser [38; 39].  
Figure 7: Change in the ratio of the contributing area based on the DEM grid cell size. (**a**) Dongkok watershed. (**b**) leemokjung watershed.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Hydroologic**} & \multicolumn{5}{c}{**Input Parameters**} \\ \cline{2-6}  & \(m\) & \(ln(T_{0})\) & \(T_{d}\) & \(SR_{max}\) & \(SR_{0}\) \\ \hline DK960616 & 0.025 & 5.0 & 49.0 & 0.1 & 0.01 \\ DK960826 & 0.019 & 2.0 & 17.0 & 0.1 & 0.01 \\ DK970715 & 0.016 & 8.0 & 15.0 & 0.1 & 0.01 \\ DK980815 & 0.032 & 1.0 & 14.0 & 0.1 & 0.01 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Applied fixed input parameter sets in the Dongkok watershed.  
Figure 8: Rainfall–runoff events by applying a constant parameter set depending on different DEM resolution values in the Dongkok watershed. (**a**) 16 June 1996. (**b**) 26 August 1996. (**c**) 26 July 1997. (**d**) 15 August 1998.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Hydroologic**} & \multicolumn{5}{c}{**Input Parameters**} \\ \cline{2-6}  & \(m\) & \(ln(T_{0})\) & \(T_{d}\) & \(SR_{max}\) & \(SR_{0}\) \\ \hline IM910525 & 0.024 & 3.0 & 6.0 & 0.1 & 0.01 \\ IM920924 & 0.027 & 1.0 & 1.0 & 0.1 & 0.01 \\ IM940801 & 0.028 & 1.0 & 14.0 & 0.1 & 0.01 \\ IM960704 & 0.016 & 3.0 & 23.0 & 1.0 & 0.01 \\ IM960825 & 0.047 & 1.0 & 10.0 & 1.0 & 0.01 \\ IM990728 & 0.016 & 3.0 & 40.0 & 1.0 & 0.01 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Applied fixed input parameter sets in the leemokjung watershed.