Optimizing regional water resources management considering ecological water demand priority for Mahaweli River watershed, Sri Lanka

This study develops an Interval Minimax Relative Regret Analysis (IMRA) method that combines interval linear programming (ILP) with minimax relative regret analysis (MRA) techniques to address growing challenges in water resources management under climate change. The proposed IMRA framework minimizes maximum potential regret among stakeholders while integrating multidimensional considerations of climate projections, risk management, and ecosystem protection, with particular emphasis on prioritizing ecological water requirements in allocation decisions. Applied to Sri Lanka's Mahaweli River Basin, the methodology employs multi-objective optimization to reconcile competing water demands across sectors and resolve disparities among diverse water users, systematically evaluating irrigation benefits and associated economic losses across 23 regions with varying crop patterns. The investigation reveals critical interactions between water resources and key socioeconomic and ecological determinants, enabling scientifically-grounded regulation and efficient utilization of water sources. Through absolute and relative regret criteria, the IMRA model identifies optimal solutions, determining an ideal irrigation water supply range of [174.09, 216.62] 10⁶ m³. Results demonstrate substantial ecological water demands in Matale and Pussellawa, constituting 36 and 40% of total regional water needs respectively under varying supply conditions, while maintaining allocation efficiency and ecosystem integrity. This study provides a robust framework for sustainable water management amidst environmental uncertainties.