Enhanced green infrastructure (GI) in urban areas, such as green roofs, parks and green spaces can make a significant contribution to enhancing the provision of fundamental ecosystem services (ES), through nature-based solutions. These positive effects include increasing the interception capacity due to increasing vegetation cover, increasing of storage capacity and infiltration of the soil, thus reducing storm water runoff, producing substantial improvements in the urban drainage system, whose infrastructure is very difficult and expensive to be modified. In this paper an indicator based on the runoff coefficient, which allows quantifying the impact on runoff due to increase of GI is presented. In a second step, a way for relating the indicator with the risk of flooding is proposed. The complete methodology was applied on an urban basin located in the north of Rosario city, Argentina. Four scenarios were evaluated: baseline scenario (current scenario), and three hypothetical (future) scenarios, considering a moderate and severe waterproofing situation respectively, and one green scenario with increased GI. The results show that the moderate and severe waterproofing scenarios produce an increased risk of flooding from 1.9 times to 4 times, respectively. This implies a necessary reinvestment in urban storm water infrastructure in order to keep the original security levels. The green scenario does keep the runoff coefficient, even considering the major increases in population and urbanization. Improving the GI constitutes a strong strategy to adapt to climate and urban changes, to cope with upcoming increases in precipitation and urbanization.
