| Abstract |
Urban drainage systems face intrinsic constraints related to the deterioration of infrastructure, the interaction between systems, and increasing requirements and stresses that lower the quality of provided services. Furthermore, climate change and the need for the efficient use of resources are providing additional pressures that cannot be addressed solely with "Business-as-usual" solutions. In this paper, the consequences of such problems and limitations on the urban environment have been assessed through the identification of linked major impacts (e.g., urban flooding and pollution events) and societal externalities (e.g., economic losses, health and social issues, and environmental risks). Since Nature-based Solutions (NBS) consider human well-being, socio-economic development, and governance principles, they open new perspectives regarding urban sustainability, quality of life, and climate change adaptation. To highlight their added value to existing Urban Drainage Systems (UDS), the synergies that result from implementing NBS with traditional urban drainage systems were identified and assessed. Based on a comprehensive framework, for both wastewater and stormwater, the relevant opportunities for rethinking UDS and NBS were identified. Most relevant positive effects go beyond the mitigation of existing intrinsic constraints of traditional systems (e.g., dealing with the control of pollutants or stormwater management) since NBS also provide important economic, social, and environmental co-benefits by including water in urban planning and providing greener open spaces. This integrated and complementary solution not only represents a contribution to the sustainable management of urban water, but also enables an increase in the resilience of urban areas and, in particular, water services against climate change and for additional social co-benefits. |