Assessment of the contribution of Nature-Based Solutions (NBS) to urban resilience: application to the case study of Porto

Nature-Based Solutions (NBS) provide a systemic approach to promote the maintenance, enhancement, and restoration of biodiversity and ecosystem services (ES) in urban areas, helping to enhance urban resilience in the water sector. Within the sustainable development goals proposed by UNHABITAT, resilience in cities was established as a critical issue. The assessment of the NBS contribution to urban resilience and the development of tools to determine the long-term value of these solutions comprise a most needed step forward. A comprehensive Resilience Assessment Framework to assess the NBS contribution to urban resilience (RAF), focused on NBS for stormwater management and control, was proposed and developed (Beceiro et al., 2020). This assessment framework aims to support the diagnosis, decision-making, implementation, planning, and management of the NBS and to identify the solutions with greater potential to contribute to city resilience drawbacks. This paper aims to demonstrate the purpose and relevance of the RAF, by presenting its application to a case study, highlighting both data demands (given different complexity requirements for metric's determination) and specific considerations regarding the level of assessment (either to the overall city area or to specific NBS). The application to the case study allows assessing the contribution to urban resilience of the main NBS in the urban area of Porto and, specifically, the contribution of an infiltration basin, which will be implemented in the Asprela catchment. Main resilience shortcomings in the city that may be upgraded by NBS are also identified, as recommendations for future urban planning in Porto. This application also intends to deliver a thorough example for other cities aiming to assess NBS contribution to urban resilience using the proposed RAF. At the city level, the main opportunities to improve the NBS contribution identified corresponded to the Governance and stakeholders' involvement, Environmental resilience and Resilience engaged service. On the other hand, the Social involvement and co-benefits and the Service management (obj.6) are identified as consolidated aspects across the urban area. At the NBS level, it was possible to conclude that the infiltration basin, considering the design characteristics, will enhance significantly the contribution to urban resilience in the Asprela catchment, based on the results for the model based metrics and the defined scenarios. Furthermore, it was possible to conclude that the NBS will operate in overall good hydraulic condition, even for the most severe rainfall conditions.