## 3 Results  
### Calibration and Validation of the Eco-Hydrological Model  
#### 3.1.1 Calibration and Validation of Runoff Component  
To validate the model's simulation performance, the well-established hydrological model SWAT (Soil and Water Assessment Tool) was also used for comparison of runoff simulations (Table 1, Figure 2). The calibration period covered the monthly runoff simulation results from 1990 to 2000, which yielded the best simulation performance, while the validation period used monthly runoff simulations from 2001-2012, consistent with the RHESys time series. The results indicate that both the RHESys and SWAT models achieved Nash-Sutcliffe Efficiency (NSE) values greater than 0.5 and Percent Bias (PBIAS) values between 25% and 25% during both the calibration and validation periods, with RHESys demonstrating superior simulation performance compared to SWAT. This suggests that the RHESys eco-hydrological model is also applicable for simulating the runoff processes in this region. However, the overall effectiveness of RHESys runoff simulations in this basin is relatively low compared to other watersheds where it has been applied [14, 52, 53]. This is attributed to the semi-arid plains in the basin's western region and the location of the watershed outlet, where most rivers are seasonal, leading to low runoff volumes and increased flow-direction uncertainty in the plains. The NSE values obtained by [PERSON] et al. [15] at the same study area also ranged between 0.5 and 0.6.  
As shown in Figure 1 and Table 1, PBIAS values during the calibration and validation periods were 18.01% and 7.22%, respectively. Thus, RHESys demonstrates poorer runoff simulation performance during the flood season, with a tendency toward.  
Understanding; in contrast, SWAT performs better during the growing (flood) season, likely because RHESys's unique vegetation growth module overestimates the negative impact of vegetation (such as infiltration and vegetation interception) on runoff production during the flood season. For the non-flood season, RHESys achieved LogNSE values of 0.70 and 0.68 for the calibration and validation periods, respectively, which were significantly higher than the SWAT model's 0.54 and 0.50 and its own NSE values of 0.61 and 0.60. Therefore, RHESys provides better simulation performance in the non-flood (non-growing) season, while SWAT performs less effectively, possibly due to the limited influence of vegetation dynamics in the non-growing season and RHESys's inclusion of deep soil water feedback processes during infiltration, which are not considered in SWAT. For this study, the ecological water demand within the river channel mainly depends on the multi-year minimum average flow. Thus, RHESys is more suitable than SWAT for studying instream EHRs in this basin.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{Parameter} & \multirow{2}{*}{**Definition**} & \multirow{2}{*}{**Initial Range**} & \multirow{2}{*}{**Evaluation**} & \multicolumn{2}{c}{**Calibration Period**} & \multicolumn{2}{c}{**Validation Period**} \\ \cline{5-8}  & & & & **Index** & & **RHESys** & **SWAT** & **RHESys** & **SWAT** \\ \hline m & The decay of vertical K with depth & 0.01–20 & NSE & 0.61 & 0.58 & 0.60 & 0.53 \\ K & Saturated hydraulic conductivity & 0–600 & PBIAS & 18.01\% & 11.28\% & 7.22\% & 23.41\% \\ po & Soil pore size index & 0.5–2.0 & LogNSE & 0.70 & 0.54 & 0.68 & 0.50 \\ pa & Soil inlet pressure & 0.5–2.0 & & & & & \\ gw1 & Percentage of infiltrated water bypass to & 0.15–0.4 & & & & \\  & the deeper groundwater store & 0.37–1.0 & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 1: Calibrated RHESys model parameters and evaluation of model performance of RHESys and SWAT.  
Figure 2: The precipitation, observed and simulated monthly runoff depth for the calibration period (January 1982–December 2000) and for the validation period (January 2001–December 2012) in the Hailar River Basin. (**a**) RHESys model; (**b**) SWAT model.