# An Estimation Method of River Dry Runoff Alteration after Upper New Reservoirs Storage
## 4 Conclusions  
Previous studies have primarily focused on the practical impacts of cascade reservoirs on downstream river hydrological characteristics, with limited attention given to the prediction of these impacts when dams are built in the future. Particularly, the estimation of runoff, a crucial factor for future engineering design, has received little attention. This paper addresses this gap by proposing an estimation method for predicting river runoff during the dry period based on the correlation between hydrological alterations and reservoir  
Figure 7: The increase in downstream river flow caused by hydropower development in the Jinsha River and Min River basins. operations. The method is validated and applied using relevant datasets from the Jinsha River and Min River basins. The developed method takes into account the differences in the increment distribution of monthly average runoff during the dry period and the bias between theoretical and practical results. By considering these factors, the method provides a comprehensive approach for predicting the impacts of dam construction on river runoff. Due to the primary objectives of reservoir operation, including flood control, water supply, electricity generation, and ecological conservation, downstream river runoff exhibited a decrease during the flood period and an increase during the dry period. The M-K trend tests and catastrophic analysis conducted on the Jinsha River and Min River demonstrated that the mutation times of monthly average discharge during the dry period corresponded to the construction of dams in the river basins. In both the Jinsha River and Min River basins, over 90% of the runoff increment was concentrated between January and May, resulting in respective runoff increments of 234-1253 m\({}^{3}\)/s and 157-541 m\({}^{3}\)/s. The proposed method was validated with deviations of 26% for the Jinsha River and 13% for the Min River, which are relatively common in studies concerning climate variations and hydrological alterations. Considering the recent construction of Baihetan and Wudongde dams in 2021, the predicted values for the average runoff during the driest month and the 95% navigation assurance runoff were 2866 m\({}^{3}\)/s and 2174 m\({}^{3}\)/s, respectively. The developed method presented in this paper offers a practical and efficient tool for researchers in the field, ensuring the avoidance of engineering invalidation and unnecessary resource costs in the future. The method requires careful consideration of the characteristics of the studied river section and the operation of the reservoir group in the application process. It relies on measured data to determine the differences between theoretical and actual runoff, rather than simply generalizing to all basins. Further research could utilize coupling models and similar approaches to refining the correlation between hydrological changes and reservoir operations, expanding the temporal scale to daily or ten-day intervals. Additionally, investigating the proportion of dry months among the total runoff increments based on the long-term impact of dams using methods such as trend analysis will provide valuable insights. This will contribute to a more comprehensive understanding of the effects of reservoir operation on hydrological patterns and enable better predictions and management strategies for water resource systems. Conceptualization, Z.C. ; Methodology, Y.D. ; Software, L.L. ; Validation, A.M.; Formal analysis, L.L. ; Investigation, Z.C. ; Resources, J.L. ; Writing--original draft, Z.C. ; Writing--review & editing, Y.H. All authors have read and agreed to the published version of the manuscript.