# An Estimation Method of River Dry Runoff Alteration after Upper New Reservoirs Storage
## 2 Background and Methodology
### Hydrological Characteristics Alteration
#### 2.2.2 Min River  
Based on the hydrologic data analysis during 1980-2020, the muti-annual average runoff discharge of Min River was 2697 m\({}^{3}\)/s; the maximum annual averaged runoff was 3430 m\({}^{3}\)/s in 2020; and the minimum one was 2010 m\({}^{3}\)/s in 2006. The total tendency of the annual averaged runoff of the Min River was more moderate than that of the Jinsha River, and the maximum was only 733 m\({}^{3}\)/s of negligible fluctuation. Because of the vicnage of the basins of the Min River and Jinsha River, the variable character of monthly average runoff alteration was basically similar in a year, namely, the flood period from June to October and the dry period from December to April of the next year. The percentage of the whole-year water volume of the flood period and dry period was 60.4% and 14.0%, respectively.  
The dry discharge variation trend of the Min River was also further analyzed by the Theil-Sen median trend method combined with the Mann-Kendall test. Through the trend test analysis of monthly average discharge of Min River in January and March. during 2006-2020, the Theil-Sen median value was calculated as 28.3, with a normalized test statistic \(Z\) of 4.48, exceeding the 95% confidence level of 1.96, which indicted that the monthly average discharge increased significantly in the dry, as seen in Figure 4a. And the M-K mutation shows that UF has always been positive since 2010, namely that dry discharge has still increased. The curves of UF and UB intersected in 2010, which was  
Figure 3: Variations in the monthly average runoff of the Jinsha River during different periods. (**a**) Monthly average runoff at different periods. (**b**) Monthly average runoff variation values.  
located in the confidence zone. Therefore, the mutation time was preliminarily determined to be 2010.  
Further, combined with the Pettitt change point test and cumulative anomaly method, it could be seen that the main inflection points emerged in 2010, consistent with the Pettitt test results. Therefore, the catastrophic time of the dry discharge was in 2010, which was just the construction time of Pubugou in the Dadu River. Hence, the construction of the dam in the Min River Basin had a significant impact on the dry discharge. Monthly average discharge in the first stage during 2006-2010 was 918 m\({}^{3}\)/s, and after the completion of the reservoir of Pubugou, the discharge in the second stage during 2011-2020 was incremented to 1223 m\({}^{3}\)/s, as seen in Figure 4b.  
Similar to the above mentioned, when the cascade reservoir conduction, Zipingpu, in Min River was built in 2006, some increment of monthly average runoff during the dry period occurred by 51-128 m\({}^{3}\)/s, and attenuation of average runoff during the flood period was 607-1676 m\({}^{3}\)/s monthly. Subsequently, when a series of dams along the Dadu River were built from 2010 to 2018 in Pubugou, Houziyan, and Changheba, the monthly average runoff variation became more obvious. The increment during the dry period was 157-541 m\({}^{3}\)/s compared with the situation of no dam construction before 2006; accordingly, the attenuation during the flood period was 441-856 m\({}^{3}\)/s, as seen in Figure 5b.  
Figure 4: Variation tendencies and catastrophic analysis of the monthly average discharged change of the Min River in the dry. (**a**) Runoff situation at different periods. (**b**) The MK test and cumulative anomaly values.  
Figure 5: Monthly average runoff and alteration during different periods of the Min River. (**a**) Monthly average runoff at different periods. (**b**) Monthly average runoff variation values.