A catchment-scale framework for nature-based solution placement using hydrological connectivity and participatory decision support

Nature-based solutions (NBS) such as wetlands are increasingly promoted as multifunctional measures for flood mitigation, water quality improvement, and ecosystem service enhancement under climate change. However, their effectiveness strongly depends on where they are implemented within the landscape, and uncertainties in spatial targeting continue to limit their performance and large-scale uptake. This study presents an integrated, catchment-scale framework for strategic NBS placement that bridges process-based hydrological science with participatory decision support.

The framework combines structural and functional landscape connectivity modelling with hydrological assessments and stakeholder-informed multi-criteria decision analysis. Sediment and hydrological connectivity are quantified using a connectivity index that integrates topography, land cover, soil properties, runoff potential, and soil moisture to identify areas of high transport activity and retention potential. Potential wetland locations are identified through high-resolution depression analysis and evaluated based on upstream-downstream interactions, storage capacity, and land-use context. Stakeholder priorities are incorporated using an analytic hierarchy process and multi-criteria decision analysis to explicitly account for governance constraints, feasibility, and desired ecosystem services.

The approach is demonstrated in two contrasting lowland catchments in central Sweden draining into Lake Mälaren, characterized by different land-use patterns, soil compositions, and hydrological responses. Results show that high-priority NBS locations consistently emerge where hydrological and geomorphological connectivity converge, highlighting the importance of targeting intervention points that influence catchment-scale processes rather than isolated sites. The multi-objective analysis reveals clear trade-offs and synergies among flood regulation, sediment and nutrient retention, water storage, and biodiversity, supporting transparent decision-making across competing objectives.

By integrating connectivity-based modelling with participatory prioritization, the framework links scientific understanding of landscape processes with practical implementation needs and policy-relevant decision support. The methodology is scalable, transferable, and suitable for application across different climatic and socio-economic contexts. It provides a robust basis for advancing climate-resilient landscape planning and supports the mainstreaming of NBS in water and land management strategies aligned with climate adaptation and sustainability goals.