Sustainable strategies for flood risk management in urban areas. Enhancing city resilience with Green Roofs

Abstract

Urbanization dynamics that affected Italian cities in the last twenty years, led to significant land use changes. This phenomenon, mainly resulted into a progressive extension of the impervious surface, gave rise to an alteration of the hydrological cycle and an increase in urban flooding phenomena. In this scenario, Sustainable Drainage Systems (SuDS) and in particular Green Roofs, topic on which experimental research activities were carried out at the University of Salerno, can be considered effective solutions useful to reduce the hydraulic risk and to enhance city resilience. Analysing land use variations of a small urban catchment in the city of Mercato San Severino (SA) it was observed a soil imperviousness increase of 18% between 1995 and 2016. This phenomenon inevitably led to an overload of the drainage network, actually affected by several criticalities, and to an increase of urban flooding. Therefore, in this context, sustainable drainage strategies able to restore the drainage pattern prior to the soil sealing, influencing stormwater generation, can be considered a valid solution for the management of an ever increasing stormwater runoff.However, in order to make the implementation of these sustainable infrastructures more effective in the management of urban flooding, a large portion of the current impermeable surface, almost 70% should be retrofitted. The preferable strategy, so, is that of using sustainable drainage systems only as mitigation techniques, aiming not at the total restoration of the conditions prior to construction but at a partial reduction of the sewer load.