Green roof storm water detention: laboratory and full-scale experiences in the Mediterranean climate

Storm water management performances of green roofs may differ in various climatic regions due to the specific precipitation climatology, building practices, and green roof materials. Although a wide range of experimental results are now available in continental or nordic climate regions, few data about green roof performances in a Mediterranean climate have been presented in the literature. To this aim the University of Genoa recently developed a joint laboratory and full-scale experiment by installing a “controlled” plot with known rainfall input and a companion green roof research site in the town of Genoa. In September 2007 the small size system was completed in the laboratory, namely a plot of 2.5 m2 aimed at performing runoff tests in a controlled environment using rain simulators, with varying slope, depth and type of soil layers. The full-scale system was obtained by retrofitting an existing single-layer vegetated roof built in the sixties into a modern technological system fully equipped with sensors for on-site meteorological and flow rate measurements. For the interpretation of the results two approaches aimed at simulating the hydraulic response of green roofs have been implemented including both a complete unsaturated flow model and a simplified conceptual model based on a limited number of parameters. The collected green roof runoff data, with an average percent retained volume of 73% and an average percent peak reduction of 92%, show the great potential for the development of green roof technologies in Mediterranean countries.