Choosing the right nature-based solutions to meet diverse urban challenges

Increasing focus on Nature-Based Solutions (NBS) in cities has significantly expanded the range of applications in which urban nature is considered useful, as well as the range of NBS available. Traditional parks, gardens and street trees now sit alongside innovative approaches including rooftop pollinator habitats, constructed wetlands and hydroponic green facades, each of which has its own particular challenges and benefits. This variety of solutions introduces an important new decision-making challenge for cities wishing to implement NBS: choosing the right set of specific NBS interventions. Decision support tools such as Multi-Criteria Decision Analysis (MCDA) can help navigate complex decisions, but their application to urban NBS selection decisions has been limited. Current NBS assessment frameworks tend to either give highly aggregated results, or are tailored to only one specific ecosystem service. Here we demonstrate a novel application of MCDA to the practical challenge of selecting a set of NBS to address multiple urban challenges. The MCDA tool developed here was used in seven cities participating in the European Union project 'Urban GreenUP'. We describe the development and use of the MCDA tool, and explore how cities used the tool to guide NBS selection. We also evaluate the tool using sensitivity analysis and feedback from users. We find that participating cities are seeking to balance a large number of possible benefits from NBS solutions, and the tool proved useful for navigating the selection decision. Users identified opportunities to improve the tool's usability and clarity. They also noted a key strength of the tool as a prompt for co-production of knowledge and decisions. Collectively, these findings advance the design and application of tools to support complex decisions about selecting NBS to address diverse urban challenges.