Integrating fuzzy-based afforestation scenarios and soil and water assessment tool to implement nature-based flood solutions

ABSTRACT Designing nature-based solutions (NBSs) for flood mitigation is inherently complex, requiring careful integration of ecological, hydrological, and spatial considerations. This study presents an integrated approach to evaluate afforestation scenarios for flood reduction by linking a fuzzy land suitability model with the Soil and Water Assessment Tool (SWAT). The fuzzy land suitability model applies a Mamdani approach to classify catchment areas according to their afforestation potential, incorporating hydro-ecological criteria alongside expert judgment. SWAT was calibrated to capture the hydrological response to land-use changes by simulating a long-term hydrological period of the Bremer River catchment, Australia. The following two afforestation scenarios were examined: (1) targeting only highly suitable areas and (2) including both highly and moderately suitable areas. These scenarios were then evaluated for their capacity to reduce flood peaks. Results indicate that SWAT accurately reproduced observed flood dynamics, with Nash–Sutcliffe efficiency values exceeding 0.5 for a long-term period. The land suitability assessment highlighted that areas classified as highly suitable are limited, implying that moderately suitable regions may need to be considered to achieve meaningful flood mitigation. The study further demonstrates that afforestation can reduce flood peaks by up to 18%, though large-scale implementation may face practical and technical limitations across the catchment.