Robust water resources management: How optimization approaches influence robust policy and operational decisions under uncertainty

It is crucial to identify robust operational policies and decisions that ensure water resources systems perform consistently well under uncertain future conditions. However, developing robust operational policies and decisions is complex due to the variety of robustness metrics that can be used to evaluate potential solutions and the variety of scenarios that are available to represent future conditions. While past optimization studies have investigated how different robustness metrics and scenarios influence operational policies and decisions, these investigations have been typically based on an optimization approach known as postoptimization robustness analysis. This approach involves optimizing policies under individual scenarios and then evaluating their robustness across all scenarios. Recently, an alternative approach - robust optimization - has been developed to integrate robustness metrics explicitly into the optimization process. However, it is unclear how robust policies and decisions obtained from robust optimization vary in response to the robustness metrics and scenarios used and how they compare to those from post-optimization robustness analysis. Therefore, in this study, we investigate how the optimization approach influences robust policy and operational decisions obtained in response to different robustness metrics and scenarios. Results based on a reservoir system in Australia show that the selection of the optimization approach can affect the resulting robust operational policies, especially under scenarios with large uncertainty. Although robust optimization generally leads to more robust operational policies, the effectiveness of these policies depends on the robustness metrics used. These findings offer valuable insights for choosing both an optimization approach and suitable robustness metrics based on future uncertainty levels, informing robust and practical operational policies and decisions.