Scaling up nature-based solutions for climate-change adaptation: Potential and benefits in three European cities

Many exemplary projects have demonstrated that Nature-based Solutions (NBS) can contribute to climate change adaptation, but now the challenge is to scale up their use. Setting realistic policy goals requires knowing the amount of different NBS types that can fit in the urban space and the benefits that can be expected. This research aims to assess the potential for a full-scale implementation of NBS for climate-change adaptation in European cities, the expected benefits and co-benefits, and how these quantities relate to the urban structure of the cities. We selected three case studies: Barcelona (Spain), Malmö (Sweden), and Utrecht (the Netherlands), and developed six scenarios that simulate the current condition, the full-scale implementation of different NBS strategies (i.e., installing green roofs, de-sealing parking areas, enhancing vegetation in urban parks, and planting street trees), and a combination of them. Then we applied spatially-explicit methods to assess, for each scenario, two climate change-related benefits, i.e. heat mitigation and stormwater regulation, and three co-benefits, namely carbon storage, biodiversity potential, and overall greenness. Finally, by breaking down the results per land use class, we investigated how the potential and benefits vary depending on the urban form. Most scenarios provide multiple benefits, but each one is characterized by a specific mix. In all cities, a full-scale deployment of green roofs shows the greatest potential to reduce runoff and increase biodiversity, while tree planting -either along streets or in urban parks– produces the greatest impact on heat mitigation and greenness. However, these results entail interventions of different size and in different locations. Planting street trees maximizes interventions in residential areas, but key opportunities for integrating most NBS types also lie in commercial and industrial areas. The results on the pros and cons of each scenario can support policy-makers in designing targeted NBS strategies for climate change adaptation.