What variables matter when designing nature-based solutions for stormwater management? A review of impacts on ecosystem services

Managing stormwater is a major concern in cities characterized by high risk of floods and water pollution. Nature-based solutions (NbS) have emerged as a valuable alternative for managing stormwater through the provision of runoff mitigation, stormwater treatment, and other ecosystem services (ES). The development of these solutions in urban areas are primarily supported by guidelines providing good practices for their design, construction, and maintenance. However, these guidelines overlook the role of specific NbS, such as urban forests, urban parks, street trees, and community gardens, which also influence the urban water cycle. To address this limitation, this research aims to identify key variables related to these solutions and assess their impact on runoff mitigation and stormwater treatment. We performed a literature review of papers that assess the hydrologic and pollution treatment performance of the selected NbS. Results provide a set of vegetation-related, soil-related, physical, and location-related variables, describing optimal characteristics that can be considered for the NbS design in several urban contexts. Based on the evidence extracted from the reviewed papers, both positive and negative effects of variables on the water-related ES and suitable indicators for each NbS type were identified, and limitations for their assessment were discussed. Finally, we highlighted the main knowledge gaps that limit the design of urban forests, urban parks, street trees, and community gardens for tackling stormwater management issues in cities.