Assessment of blue green infrastructure implementation schemes for multifunctional urban stormwater management: a case study in three Swedish cities

Blue-Green Infrastructure (BGI) in urban areas is primarily designed for stormwater management, but it also offers multifunctional benefits that support environmental, social, and economic sustainability. This study evaluates the benefits of seven BGI design alternatives in three types of urban areas in Sweden, representing typical cases in many parts of the world: Inner City catchment, Residential Suburbs, and New Urban Housing development. Long-term benefits (normalized per capita) were assessed and monetized using the Benefits Estimation Tool (CIRIA - UK Construction Industry Research and Information Association). Common benefits in all area types included Amenity, Education, Flooding, Health, Water quality, and Water quantity. The greatest benefits were realised in Residential Suburb and Inner City areas, particularly with BGI schemes based on open dry detention or bioretention with swales. Benefits were less pronounced in the New Urban Housing area. Sedimentation ponds and bioretention facilities performed best in the Residential Suburb. Net Present Value (NPV) was positive in the Inner City and Residential Suburb areas, but negative in the New Urban Housing area, indicating lower cost-effectiveness. Benefit-Cost Ratio calculations indicated that the per capita return on investment for constructing BGI is highest in Residential Suburbs even though the NPV was greatest in Inner City areas. The methodological framework and results are discussed in the light of making the findings transferable to other European cities and international contexts with similar environmental and urban characteristics.