What is controlling our control rules? Time-varying sensitivity analysis reveals the importance of adaptive and coordinated information use for multi-reservoir operations

Multi-reservoir systems must serve multiple conflicting demands over varying time scales that may be out of phase with the system's hydroclimatic inputs. Furthermore, both the reservoir supplies and demands may be nonstationary, necessitating the use of adaptive reservoir control policies. Yet while river basin objectives and inputs are dynamic, traditional operating rules are static, ignoring the potential for adaptive and coordinated information use to reduce conflicts between the system's multisectoral demands. In this study, we use time-varying sensitivity analysis to show how recent advances in multi-objective control enable the design of coordinated multi-reservoir operating policies that continuously adapt their release prescriptions as a function of evolving hydrologic inputs. Interestingly, these information sensitivities vary significantly across policies depending on how they negotiate tradeoffs between conflicting objectives. We illustrate this analysis in the Red River basin of Vietnam, where four major reservoirs serve to protect the capital of Hanoi from flooding while also supplying farmers with irrigable water supply and the surrounding region with electric power. Utilizing Evolutionary Multi-Objective Direct Policy Search (EMODPS), we are able to design policies that, using the same information as sequential if/then/else-based operating guidelines developed by the government, outperform the prescribed operational rules with respect to every objective. Policy diagnostics using time-varying sensitivity analysis illustrate how the EMODPS operations better adapt and coordinate information use to reduce food-energy-water conflicts in the basin. These findings accentuate the need to transition from static rule curves to dynamic operating policies in order to manage evolving hydroclimatic variability and socioeconomic demands.