Prioritisation of nature-based solutions in urban catchments

Nature-based solutions (NBS) are gaining traction around the world, as cities and institutions transition towards sustainable development. NBS provide opportunities to use infrastructure based on natural processes to manage the urban water cycle, improve biodiversity and social outcomes. However, NBS are complex with multiple benefits and constraining factors to consider. Presently, there is a recognised lack of NBS planning support tools available to help institutions make strategic decisions. For public authorities, there are three key questions to answer: Which locations should be selected for NBS? Which type of NBS should be implemented? How much performance can be expected? The objective of this study was to prioritise large-scale nature-based solutions within a case-study area in the City of Helsinki. The developed methodology built upon international research seeking to improve the systematic and holistic planning of NBS. The project used a multi-criteria assessment (MCA) framework to prioritise sub-catchments and rank identified NBS opportunities. The framework comprises of spatial data indicators for water quantity, water quality, amenity and biodiversity. A methodology for combining these indicators was developed to produce an overall NBS priority score for sub-catchments within the city. The study used spatial analysis to identify specific locations for large-scale NBS assets and rank their performance using the MCA framework. Using the sub-catchment analysis and opportunity performance scores within the MCA framework, opportunities were assessed and ranked according to their ability to respond to drivers in their catchments and deliver multi-criteria benefits. The key results of the study are the locations, asset types and expected relative performance of nineteen large-scale NBS opportunities within the Mätäjoki case study area. These opportunities were prioritised to highlight sites with the potential to deliver the highest multi-criteria performance. The results will assist the City of Helsinki to direct investment towards those NBS opportunities that provide the largest benefits for society and avoid investment in lower performing assets