Operationalizing equity in multipurpose water systems control

Participatory decision-making is a well-established approach to address the increasing pressure on water systems induced by growing multi-sectoral demands and increased competition among different water users. Yet, most existing approaches search for system-wise efficient solutions and do not quantify their distributional effect among the stakeholders. In this work, we investigate how to operationalize equity principles to design improved water systems control policies that better balance efficiency and justice. More specifically, we analyze alternative problem formulations with different number of objectives, i.e., shifting from a traditional multi-objective to a many-objective control, and with/without the inclusion of an equity index among the objective functions. The multi-purpose operations of Lake Como in Italy, accounting for flood control and water supply along with so far marginalized services such as prevention of low levels and ecosystem preservation downstream of the lake, is used as a case study. Our results show how incorporating equity considerations into the design of optimal control policies enriches the solution space by generating more compromise solutions than those obtained using a traditional multi-objective approach. Moreover, we find that including equity in the control policy design can indirectly improve the performance of marginalized sectors, such as recreation and ecosystem, which are not explicitly considered by the current lake operation. Lastly, we illustrate how the aggregation of multi- sectoral interests into an equity index strongly shapes our results. The adoption of participatory approaches for eliciting the preference structure of stakeholders and policymakers thus becomes paramount for the operationalization of equity principles to re-scale the objectives and represent a fair balance across competing interests. This work bridges the gap between multi-objective optimal control approaches and equity-informed decision-making for real-world water resources planning and management, providing an effective tool to promote efficient and equitable policies.