Green Roofs as an alternative solution for stormwater management in Turin, Italy

Urban stormwater has been increasing significantly in recent years due to drastic changes in climate and the environment as a result of the increased presence of paved surfaces. In highly urbanized areas, where impermeable surfaces dominate, surface runoff can lead to frequent flooding and bring serious challenges for stormwater management. Green roofs have emerged as an effective strategy to mitigate stormwater runoff while offering additional ecological benefits. This thesis examines the hydrological performance of green roofs under historical and future climate scenarios, over a 65-year projection, in four different cases under identical meteorological conditions for the city of Turin, Italy. Climate data, including historical observations (1981-2006) and future projections based on the IPCC RCP 4.5 scenario (2006-2070), were obtained from the Euro-Mediterranean Center on Climate Change (CMCC) as part of the Highlander project, which employs convection-permitting regional climate models (CP-RCMs) at a spatial resolution of approximately 2.2 km. These models are particularly innovative due to their ability to simulate convective precipitation at an hourly timescale, making them highly effective for assessing future climate impacts. The Green Roof model analyzed features a surface area of 16 m2, with a multilayered structure comprising a total thickness of 19 cm, of which 9.5 cm is a loamy soil substrate. With a soil porosity n of 0.43, the active soil depth (nZr) is approximately 40 mm. The analysis evaluates three vegetation types: sparse succulent, dense succulent, and herbaceous, by varying the crop coefficient (Kc), and in one scenario, doubling the active soil depth (nZr) to assess its impact on runoff reduction. Results indicate that vegetation with a higher crop coefficient (Kc1) leads to increased effective evapotranspiration and a corresponding reduction in runoff. Herbaceous vegetation, in particular, was found to reduce runoff volume by 12% compared to sparse succulent vegetation. When doubling the active soil depth (nZr) further reduces runoff by 11%, attributed to the increased water retention capacity of the system. These findings provide valuable insights into optimizing Green Roof designs for improved stormwater management in urban areas.