Nature-based solutions for coastal protection based on intuitionistic fuzzy group decision making

Nature-based Solutions (NbS) use natural processes to address social, economic, and environmental challenges, including climate change, and this study explores their application for coastal protection. Before the actual implementation of NbS structures, co-creation with stakeholders to identify and assess potential NbS solutions for the selected local site is essential. However, existing frameworks for selecting NbS measures in coastal protection remain limited in handling the complex interactions among multiple indicators and the inherent uncertainty in expert evaluations. To address this gap, we develop an integrated assessment framework specifically for NbS in coastal protection. We first identified 18 distinct coastal protection measures through literature reviews. The proposed framework combines the Fuzzy Delphi Method (FDM) and entropy-based intuitionistic fuzzy TOPSIS (IF-TOPSIS) to facilitate expert-driven multi-criteria decision analysis (MCDA), both of which use fuzzy theory to address uncertainty and ambiguity in expert judgments. The 18 consensus indicators from an initial pool of 63 evaluation indicators are obtained in FDM analysis. Subsequently, IF-TOPSIS is applied to rank the 18 measures against these evaluation indicators based on membership, non-membership, and hesitancy degrees. The proposed framework is demonstrated through a case study at the Golden Coast, Tainan, Taiwan to illustrate its practical applicability.