System Dynamics Model for Assessing the Water Dynamics and the Capacity of Large Reservoirs to Supply Multiple Uses

Abstract Large reservoirs play a crucial role in regulating global water availability, with a storage capacity equivalent to 2% of the world’s surface freshwater, while covering only 0.33% of the Earth’s land surface. These hydraulic infrastructures supply 42% of global irrigation and are vital for domestic, industrial, and energy production purposes. In Brazil, the water demand of large reservoirs in the São Francisco River Basin is expected to increase substantially by 2050. This study aimed to evaluate the water dynamics of a large reservoir and its capacity to meet multiple uses over time. The study was conducted at the Três Marias Hydropower Plant (HPP) reservoir, located in the São Francisco River Basin, Brazil. For this purpose, a System Dynamics model was developed to quantify all inflows and outflows of the reservoir and simulate different operational scenarios, including the application of hedging strategies and the reduction of evaporation rates. Daily inflow and withdrawal data from January 2004 to June 2024 were used. The developed model was calibrated and validated using historical data on water level variations. Overall, the results highlight that the proposed System Dynamics model is a valuable tool to support strategic planning and decision-making in the management of large reservoirs. In the case of the Três Marias HPP, the application of the model revealed the need for adaptive operational strategies capable of reconciling hydropower generation with increasing consumptive uses and the maintenance of environmental flows. This study contributes to strengthening the scientific and practical foundation for integrated water resources management through the implementation of more sustainable operational rules. Finally, it is emphasized that the combination of trigger and cut-off rules, associated with minor evaporation control, can improve the balance between energy generation and meeting multiple water uses.