Using SAR Satellite Imagery for Potential Green Roof Retrofitting for Flood Mitigation in Urban Environment

Green roofs (GRs) represent a valid tool to mitigate the negative effects of urban floods. The aim of the present work is to test the hydrological behaviour of GRs at basin scale using Storm Water Management Model (SWMM), with an application to Preturo municipality located within the Sarno river basin (southern Italy) which during the last two decades was interested by the occurrence of many hazardous flash floods. The analysis of two sets of satellite images acquired between 1995 and 2016 by SAR sensors, showed a correlation between the increase of soil sealing and the occurrences of urban flooding during the same period. This finding suggests that the GR extensive adoption could contribute to a successful stormwater management. The suitability for GR retrofit depends on a number of criteria. In Preturo municipality, the fulfilment of these criteria was investigated using satellite images from Google Earth. The GRs retrofit potential of the studied area amounts to 7% of the total surface. The hydrological behaviour of the GR retrofit scenario was compared to the reference one which considers the actual land cover. The GR scenario better performs than the traditional one with a reduction of the runoff volume and peak flow of respectively 3.5% and 18.9% and an increase of the delay time of 8.2%.