## 3 Results
### Simulation Results of the Daily FTOP Model
Figure 4: Comparison diagram of observed flow and simulated flow of FTOP, NTOP, and ITOP models. (**a**–**c**) respectively compare the simulated daily flow of FTOP, NTOP, and ITOP models with the measured flow. The daily average flow of the Chengcun Basin from 1989 to 1996 was divided into the high flow section, medium flow section, and low flow section according to the flow frequency curve in order to illustrate the simulation effect of the FTOP model on different flow levels. The high flow section was below 10% of the flow frequency curve. The medium flow section was the segment between 10% and 50%. The low flow section was the part that was higher than 50%. It can be seen from Table 4 that in the high flow section, the simulation effects of the three TOPMODEL models were comparable without showing unique advantages. However, in the medium and low flow sections, the simulation effect of the FTOP model was better than the other two kinds of TOPMODEL models. In the medium flow section, the NSE, RE, and RMSE of the FTOP model were only 0.72, \(-\)20.34%, and 7.61 m\({}^{3}\)/s, respectively, being significantly better than the NTOP model and ITOP model. In the low-flow section, although the simulation effect of the FTOP model was worse than that of the high-flow and medium-flow sections, the NSE was even more harmful. However, compared with the NTOP model and ITOP model, the simulation effect was still better. Figure 6 depicts the comparison of flow accumulation curves of three TOPMDEL models simulating different levels of flow. When the curve shown in Figure 6 was closer to the diagonal (that is, the dotted line in Figure 6), it indicated that the simulation was preferable, and vice versa. As seen from Figure 6, no matter the TOPMODEL model in question, the distance between the curve and the diagonal became larger from left to right. This shows that the simulation effect of the TOPMODEL model was better in the high-flow section, and the simulation effect worsened with the decrease in flow. In the high-flow part, it can be seen from Figure 6a,d,g that the distance between the simulated data and the diagonal line was not much different, indicating that the simulation effect of the FTOP model was similar to that of NTOP model and ITOP model. In the middle-flow section, the distance between the black line and the diagonal was smaller than that between the blue line and the red line, indicating that the simulation of the FTOP model was slightly better than that of the NTOP model and the ITOP model. The FTOP model performed similarly in the low-flow section, and the improvement was pronounced. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline  & \multicolumn{3}{c}{**NSE**} & \multicolumn{3}{c}{**RE**} & \multicolumn{3}{c}{**RMSE**} \\ \cline{2-10}  & **FTOP** & **NTOP** & **ITOP** & **FTOP** & **NTOP** & **ITOP** & **FTOP** & **NTOP** & **ITOP** \\ \hline High flow section & 0.86 & 0.85 & 0.89 & 2.91\% & 7.26\% & 7.46\% & 45.33 & 46.80 & 39.64 \\ Medium flow section & 0.72 & 0.42 & 0.20 & \(-\)20.34\% & \(-\)49.58\% & \(-\)30.23\% & 7.61 & 10.97 & 12.91 \\ Low flow section & \(-\)0.68 & \(-\)3.60 & \(-\)3.82 & \(-\)91.96\% & \(-\)207.41\% & \(-\)127.56\% & 2.83 & 4.68 & 4.79 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Statistical index comparison table of three TOPMODEL models. Figure 5: Scatter plots of observed flow and simulated flow of FTOP, NTOP, and ITOP models.