A Method to Prioritize and Allocate Nature-Based Solutions in Urban Areas Based on Ecosystem Service Demand

Mapping and assessing the demand for ecosystem services (ES) in urban areas can support the allocation of nature-based solutions (NbS) to deliver ES where they are most needed. This study presents a method that combines the spatial assessments of ES demand and numeric scores reflecting the capacity of different typologies of NbS to supply multiple ES. The method was applied in 220 ha of potential NbS sites across the urban area of Valletta, Malta, considering 11 NbS types and 5 priority ES. The proposed approach supports both the prioritization of potential NbS sites and the allocation of the specific NbS types which maximise the benefits by providing the best balance of multiple ES. Results show that urban forest is the most needed NbS type across the study area, being the one with the highest capacity to supply most of the analysed ES. However, there are specific cases in which other typologies are more suitable. These include hotspots of demand for specific ES, such as noise reduction and nature-based recreation; as well as sites where size, shape, or land use constraints hinder the implementation of urban forests. Our approach can be used and adapted to support a variety of planning decisions dealing with the prioritization and spatial allocation of NbS, including the development of performance-based approaches aimed at integrating NbS within urban transformation projects.