Blue-Green Roofs: Hydrological Evaluation of a Case Study in Viterbo, Central Italy

Abstract

Green roofs can create more resilient hybrid infrastructures for the sustainable management of urban stormwater. Their permeation in urban design and planning practice depends on the roof capability in supplying multiple ecosystem services that are mainly affected by water availability and management. The blue-green roof is an innovative solution coupling a water storage below the green roof able to gather infiltrated rainfall and slowly release it out of the system. Infiltrated rainfall is then reused by green roof vegetation by capillary irrigation allowing plants survival in the dry period, increasing evapotranspiration and producing a cooling effect. The roof storage allows reducing flooding risk and overload of drainage system through storing and gradually releasing of water. This paper presents a simulation of different scenarios of green and blue-green roof in Viterbo (Central Italy) during critical rainfall. Results demonstrate (a) the almost double efficiency of the blue-green roof in reducing runoff with respect to the traditional green roof and (b) the benefits of an increased storage capacity of the blue-green roof in terms of runoff control. Future research lines for blue-green roof systems are reported and some urban planning considerations are suggested for the study area.