Nature-based solutions for urban challenges: A simple framework based on ecosystem services for a World Heritage City

• Framework based on multiple criteria to improve Nature-Based Solutions to enhance the delivery of ecosystem services. • Four types of NBSs commonly used in urban nature projects are assessed. • Ensures the minimum performance of NBSs for addressing climate change and biodiversity loss. • Validated by the municipal technical staff of a World Heritage City. • Enables the prioritisation of NBS types based on their multifunctionality scores. Urban nature projects are becoming increasingly common in cities as they contribute to reducing the impacts of the climate crisis. In this study, we developed a conceptual framework based on ecosystem services (ESs) to analyse how urban naturalisation actions (nature-based solutions, NBSs) included in urban nature projects contribute to multifunctionality. Here, multifunctionality refers to the capacity to generate multiple simultaneous ESs, indicating the extent to which the challenges identified in a city have been addressed. A multi-criteria analysis based on socioeconomic and environmental criteria, assessed using a series of descriptors linked to ESs, was used to develop a Multifunctionality Nature Project (MuNaP) index. The framework identifies the level of multifunctionality of NBSs and incorporates information for its improvement, if necessary. To validate this proposal, we calculated the multifunctionality of an urban nature project in the World Heritage City of Salamanca, Spain. Among all NBSs used in the project, tree planting was the most multifunctional, whereas the creation of bioretention sites was the least multifunctional. Increasing the values of certain criteria, such as diversity and origins, increased the multifunctionality of the urban nature project. Finally, the MuNaP index has a minimum value that ensures the multifunctionality of an urban nature project, that is, its contributions to biodiversity conservation, provision of multiple ESs, and the well-being of citizens.