## 2 Materials and Methods  
### Characteristics of Changes in Extreme Precipitation Events in the Lower Jinshajiang River Basin  
Four reservoir areas in the lower reaches of the Jinshajiang River (Xiangjiaba, Xiluodu, Baihetan, Wudongde) and thirty national meteorological observation stations (Wudongde: 6; White Crane Beach: 9; Xiluodu: 6; Xiangjiaba: 9) were selected for our study. Rainfall data from 1961 to 2020 were compiled for spatiotemporal analysis using representative extreme climate indexes defined by climate change detection and index experts (ETCCDI) following procedures jointly established by the World Meteorological Organization (WMO) and the World Climate Research Program (WCRP). Nine extreme precipitation index were finally selected for analysis as detailed in Table 1.  
The time series and trend characteristics of extreme precipitation indices in the last 60 years in 9 typical regions of the lower Jinshajiang River Basin were studied in which the trend characteristics of several extreme precipitation events are not significant (Figure 1). However, the number of heavy rain days, extreme heavy rain days and rainstorm days from 1961 to 2020 can reach 40, 20 and 4 days, respectively, and the total and extreme heavy precipitation totals reach 400 mm and 150 mm, respectively, as shown in Figure 1 and Table 2. An increase in the CDD indicates an increase in drought in the lower Jinshajiang River Basin. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Index** & **Definition** & **Unit** \\ \hline Maximum Continuous Drought Days & Maximum consecutive days without & \\ (CDD) & precipitation per year & day \\ Maximum Continuous Rainfall Days & Maximum continuous effective & \\ (CVD) & precipitation days per year & year \\ Maximum one-day precipitation & & \\ (RX1 day) & Maximum one-day precipitation per year & Mm \\ Maximum five-day precipitation & Maximum annual precipitation for five & \\ (RX5 days) & consecutive days & Mm \\ Heavy precipitation (R95P) & Total daily precipitation greater than 95\% & Mm \\  & of the sub-sites in the base period per year & \\ Extreme Heavy Precipitation (R99P) & Total daily precipitation greater than 99\% & Mm \\  & of sub-sites in the base period per year & \\ Rainstorm days & Number of days with daily precipitation of & day \\ (R50 mm) & 50 mm or more per year & day \\ Number of days with moderate rain & Number of days with daily precipitation of & day \\ (R10 mm) & 10 mm or more per year & day \\ Heavy rain days & Number of days with daily precipitation of & day \\ (R20 mm) & 20 mm or more per year & day \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Definition of extreme precipitation classifications. Figure 2 shows the time series characteristics of the extreme precipitation events for the nine lower Jinshajiang River hydropower reservoirs, with four reservoirs showing a consistent overall change in the extreme precipitation events. Here, r10 mm and r20 mm show that the four reservoirs have similar extreme precipitation day characteristics, with a maximum of 40 and 20 days, respectively, while r50 mm shows that the number of extreme rainstorm days in the Xiangjiaba reservoir is significantly higher than the other reservoirs at 6 days. The same extreme precipitation characteristics can be seen in Rx1 day, Rx5 day, R95p and R99p, i.e., the extreme precipitation is higher in the Xiangjiaba reservoir area. CDD indicates that the number of dry days is higher in the Wudongde reservoir area, which is related to the relatively low extreme precipitation in the Wudongde compared to the other reservoirs at Rx1 day, Rx5 day, R95p and R99p. In summary, extreme precipitation in the lower Jinshajiang River hydropower reservoir area is more prominent in the Xiangjiaba reservoir area, and persistent dryness is more prominent in the Wudongde reservoir area, indicating overall aridity in Wudongde in the lower Jinshajiang River reservoir area.