## 3 Results
### Intream and Off-Stream EWRs  
#### 3.2.1. Instream EWRs and Their Impact Factors  
We obtained the calculated multi-year monthly instream EWRs in the Hailar River Basin, along with the instream EWRs under scenarios without vegetation dynamics and without lateral flow redistribution (Figure 6). Between April and October, the instream EWRs are relatively high, with each month contributing over 9% of the total, summing to 94.50% of the annual EWRs. In contrast, the instream EWRs in January, February, and March are exceedingly low, at 8, 9, and 5 million m\({}^{3}\), respectively, with a marked decline compared to April to October and lower than in November and December. This seasonal gap highlights the substantial drop in precipitation after the rainy season, resulting in very low average monthly runoff within the channel. Therefore, water allocation strategies in  
Figure 4: Spatial comparison of ET results from different sources: (a) MODIS; (b) modeling RHESSys.  
Figure 5: Comparison between RHESSys simulated GPP and MODIS GPP.  
the basin should prioritize the conservation of instream water resources from January to March to maintain ecological balance. Previous studies have shown that the competitive relationship between evapotranspiration and runoff can result in an approximately 20% decrease in runoff [33; 50].  
Under the assumption of no vegetation dynamics, the multi-year average instream EWRs are 951 million m\({}^{3}\), exceeding the observed multi-year average of 711 million m\({}^{3}\). This increased demand reflects a scenario where the basin's vegetation is unaffected by current climate and hydrological conditions, resulting in increased runoff in the channel from 1982 to 2012. Consequently, climate conditions and vegetation dynamics between 1982 and 2012 acted together to restrict the increase of water volume within the channel. These vegetation dynamics imply that precipitation redistribution supports vegetation growth and prevents vegetation mortality. Research has shown that bare land has significantly lower infiltration capacity compared to vegetated land [54; 55; 56; 57; 58]. The RHESys model incorporates the return flow of infiltrated water, resulting in higher runoff under constant parameters. This effect is especially notable in the Hailar River Basin, where the predominance of deciduous and herbaceous vegetation, with relatively short life cycles, leads to significant cumulative mortality of vegetation over time.  
In the scenario without lateral flow redistribution, the basin's instream EWRs decrease to 281 million m\({}^{3}\), a reduction of 60.50%, indicating that lateral flow redistribution plays a substantial role in contributing to instream EWRs, while vertical water redistribution contributes only 39.50%. Furthermore, Figure 7 illustrates the impact of temperature and precipitation on instream EWRs. For temperature, a strong linear relationship is observed between monthly average temperature and monthly average instream EWRs under observed conditions, with an R\({}^{2}\) of 0.93 (\(p<0.01\)). This demonstrates that the method used in this study effectively captures instream EWR conditions, as higher temperatures increase surface water evaporation and biological activity, thereby elevating water demand. Conversely, precipitation and instream EWRs exhibit a logarithmic relationship, with an R\({}^{2}\) of 0.95 (\(p<0.01\)), explaining the variation in instream EWRs. When precipitation is high, instream EWRs reach a relatively stable value without further increase.  
In the scenario without vegetation dynamics, the correlation between temperature and instream EWRs significantly weakens (R\({}^{2}\) = 0.79, \(p<0.05\)). This may be due to the lack of vegetation mortality during the non-growing season, as vegetation in this scenario remains unaffected by current climatic and hydrological conditions.  
Figure 6: Variation of monthly instream EWRs in different scenarios.