Simulating the impact of nature-based solutions on runoff control by using i-Tree Hydro: a case study in Padua (Italy)

The progressive soil sealing in urbanized areas increases runoff due to surface imperviousness and leads the traditional drainage systems to a critical level, increasing flooding phenomena. The adoption of nature-based solutions (NBS) can mitigate the risk of flood and increase territorial resilience to climate change. As part of the preparation of the Green Plan of the municipality of Padua (Italy), a simulation of the hydrological balance was carried out using i-Tree Hydro software to assess the effect of the increase of permeability due to the inclusion of NBS. The potential for improving the infiltration capacity relative only to urbanized surfaces was estimated considering three types of NBS: rain garden, green roof, and permeable pavement. The amount and the surfaces potentially improved with NBS have been calculated through the application of i-Tree Canopy. The simulation covered the years from 2014 to 2019. More precise analyses for an exceptional event that occurred in May of 2018 and an intense event that occurred in May of 2019 were conducted. The analysis demonstrated positive effects of the implementation of NBS on the management of rainwater runoff volumes, more accentuated in areas with a higher degree of urbanization. From the tested NBS, rain gardens were more effective in reducing runoff (about 34-41% on average) than permeable pavements and green roofs (about 25-35 and 15-26% on average, respectively), while the higher values were observed for the intense event. Permeable pavements, better accompanied by the presence of vegetation, could be used to maximize the benefits of a NBS urban design