Urban stormwater runoff reduction by green roof under different climate conditions

Green roof is a technology able to give a big contribution to the reduction of stormwater runoff in urban areas where the occurrence of flash flood is increasing because urbanized areas are quickly replacing natural places with a consequent huge increase in impervious surfaces. In this study it is assessed how runoff reduction of an virtual green roof can vary under different weather conditions, depending on the characteristics of precipitation and evaporating power of the atmosphere. The aim of this paper is to compare the hydraulic performances of such urban green infrastructure for different climate conditions. In particular, the Mediterranean and Oceanic climate settings have been considered, with the use of local weather data to run long term and seasonal simulations. The green roof provides good performances in both climatic conditions, even though it seems to outperforms in northern latitude climates, as in some seasons there can be a total mitigation of runoff. To improve the performances, in terms of runoff reduction, of Mediterranean areas, the depth of the greening rooftops and therefore its weight has to deeply increase, entailing an increase green infrastructure and underlying traditional concrete roof costs.