Developing Robust Management Pathways for Nutrient Pollution in Watersheds Under Climate Uncertainty

Abstract Nutrient management represents an enduring effort toward sustainability. However, long‐term management planning faces notable challenges, mainly due to substantial investments required under uncertainty of forthcoming climate. To address these challenges, this paper proposes and tests a Multi‐climate‐scenario (MCS) Multi‐epoch Multi‐objective Planning (MEMOP) framework (in combination MCS‐MEMOP). This framework divides the long‐term planning horizon into multiple epochs, allowing nutrient mitigation measures (e.g., fertilization management, filter strip) to be initiated at any epoch, each with its own water quality and investment constraints. To tackle climate uncertainty, it incorporates principles of Robust Decision‐Making. MCS‐MEMOP generates solution pathways outlining the timeline and progression of management measures, tested here for a case of a small, agriculture‐dominated watershed. Considering a single climate scenario, the MEMOP method was compared with Multi‐objective Planning (MOP) and Stepwise MOP (SMOP) for a 25‐year nutrient management horizon, using the SWAT model to evaluate the test case water quality effects of solution pathways. Results show that MEMOP's multi‐epoch approach generates a larger and more diverse set of solutions than MOP and SMOP, offering greater flexibility to select optimal trade‐offs among objectives. Additionally, MEMOP solutions exhibit superior cost‐effectiveness compared to MOP and SMOP solutions. Applied separately to different climate scenarios, the MEMOP results show that changed climate conditions may significantly alter the Pareto front. In contrast, MCS‐MEMOP yields robust solutions that can consistently satisfy 72%∼89% of epoch‐specific constraints under new climate conditions in the test case, with a cost increase of 12% that reflects the price of addressing climate uncertainty in this case.