Potential of Green Roofs to Support Urban Rainwater Management: Hydraulic Experimental Assessment

Green roofs are one of the most widely used nature-based technologies, but there are no consolidated design standards to estimate their rainwater volume retention at both the national and international levels. So, the goal of this study is to analyze the annual rainwater retention capacity of different types of green roofs based on experimental real-time monitoring data collected for 12 months. The experimental setup was installed at Ballerup in Denmark and consisted of three pitched roofs, each one with 25 m2 of surface area. The green roofs presented variations in their annual rainwater retention capacity, ranging from 20% to 50%. Peak flow attenuation varied from 10% to 90% in both green roofs, depending on rain intensity and the duration of dry periods. These findings can be used as a baseline to support future studies addressing the definition of design standards and guidelines.