Collaborative modeling for groundwater sustainability evaluation in coastal aquifers using simulation optimization

Abstract Sustainable groundwater management of coastal aquifers is challenging due to saltwater intrusion, climate change, and diverse societal preferences. This requires approaches that are both scientifically rigorous and socially legitimate. This study introduces a stakeholder-informed simulation–optimization framework, which directly integrates collaborative modeling with stakeholders into the core formulation of the simulation optimization problem, unlike traditional approaches that treat participation as a separate or post hoc step. Applied to the Pearl Harbor aquifer in Hawai‘i, the modeling team and water managers co-designed the simulation optimization decision variables, objectives, constraints, and scenario analysis, ensuring that research outputs would inform real-world decision-making. More specifically, the integration embedded management settings and goals, societal values, and ecological thresholds in the simulation optimization to co-define feasible solutions, thereby enhancing model credibility, legitimacy, and salience. Results show that projected climate change under a dry scenario with sea-level rise could reduce sustainable groundwater withdrawal by up to 46% by mid-century due to saltwater intrusion. The stakeholder-informed simulation optimization mitigates these impacts, improving freshwater availability by up to 30% compared to non-optimized approaches. Combining optimization with nature-based solutions like watershed restoration through forest protection and corridor development provides synergistic benefits, adding up to 10% more sustainable yield. The framework also quantifies key policy trade-offs, such as the balance between maximizing withdrawal and maintaining spring discharge for ecological and cultural uses. By operationalizing stakeholder knowledge within the simulation optimization framework, this work offers a transferable collaborative modeling framework for advancing groundwater sustainability in coastal regions worldwide.