## 4 Conclusions  
In this paper, the DT algorithm was applied to formulate reservoir flood control operation rules that fully consider the influence of reservoir management experience, climate factors, and subsurface conditions of the watershed on discharge, realizing a fast and effective operating scheme that responds to various inflow scenarios under different hydrological periods. The following conclusions were obtained from this study:  
1. The C4.5 algorithm was used to construct DT-based flood control operation rules for a reservoir. This algorithm has the advantages of easy implementation and strong operability and fully considers the influence of the climate and underlying surface conditions of the watershed as well as the operating experience of management in the process of constructing an operating scheme.
2. As can be seen from the results of the four verification samples, the maximum discharges of the operating schemes formulated using the DT-based rules with the flood number 22 July 2020, 13 Aug 2021, and 26 Aug 2021 are the smallest; the maximum discharge with the flood number 12 Aug 2019 is smaller than that of the operating scheme formulated using the conventional operation rules and only 5% larger than the measured maximum discharge. The maximum water levels of the operating schemes formulated using the DT-based rules with the flood numbers 12 Aug 2019 and 26 Aug 2021 are between those of the measured values and the operating scheme formulated using the conventional operation rules; the maximum water level with the flood number 22 July 2020 is the smallest; the maximum water level with the flood number 13 Aug 2021 is only 0.02% larger than the measured maximum value. To sum up, the operating scheme formulated using the DT-based rules was feasible and, in some cases, superior to the actual operating scheme and an operating scheme based on conventional operation rules. Among optimization algorithms, DT-based rules have the advantages of strong and convenient adaptability, allowing decision makers to guide real-time reservoir operation. Therefore, the DT-based method for constructing reservoir flood control operation rules proposed in this paper can provide practical guidance for the real-time operation of reservoirs.  
* In this paper, only one reservoir is taken as an example, and future research should be popularized and applied in more reservoirs and reservoir group systems to verify the feasibility and effectiveness of this method.  
Conceptualization, Y.D. and Y.L.; methodology, Y.D. and H.W.; investigation, Y.D. and C.W.; data curation, C.W.; writing--original draft preparation, Y.D. and H.W.; writing--review and editing, Y.L.; funding acquisition, Y.D. and Y.L. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Key Technology Research and Development Program of Shandong Province, grant number 2019 GSF111043; the National Key Research and Development Program of China, grant number 2018 YFC1508104; the National Natural Science Foundation of China, grant number 52079079; and the Natural Science Foundation of Jiangsu Province, grant number BK20191129.  
Not applicable.  
The datasets used and/or analyzed during the current study are available from the corresponding author upon reasonable request.  
We express our deepest gratitude to the Rizhao Reservoir Management and Operation Center for their help in data support.  
The authors declare no conflict of interest.