Green roof flood mitigation in the Mediterranean region

Many studies have shown that green roofs provide a number of benefits to urban areas. Flood mitigation is one of such benefits, due to the potential of green roofs to absorb and retain precipitation. The volume of water retained by the substrate influences runoff. The depth and water content of the substrate also contribute to the extent by which flooding is mitigated. This study presents the results of a monitoring activity which took place on two demonstration green roofs sited in two Mediterranean regions (Malta and North Italy) and of tests carried out in a rainfall simulator at various rain intensities using different substrate depths. On the Italian green roof, the substrate moisture content affected the runoff coefficient and the water retention. Substrate depth and properties influenced the runoff coefficient. Biochar, used as a component in some substrates, showed influences on water retention and runoff delay.