The effect of Sustainable Urban Drainage Systems on outdoor comfort and runoff

Cities are facing numerous challenges such as Urban Heat Island Effect (UHIE) and more frequent flooding events, due to the increasing soil sealing. Greenery and water implemented in urban outdoor spaces have been promoted as effective strategies to counteract UHIE while Sustainable Urban Drainage Systems (SUDS) have been identified as convenient solutions to increase resilience to flooding. However, since many SUDS are green-based, they also benefit urban microclimate and outdoor thermal comfort. In this work, the effectiveness of SUDS as passive strategies to simultaneously improve outdoor thermal comfort and reduce stormwater runoff is assessed. The analysis is carried out on a neighbourhood in Ostia (Rome), selected as representative of Mediterranean climate. The case study area is modelled on ENVI-met in three different scenarios: the current condition is compared with two future developments in which green and water-based mitigation strategies are implemented or in which soil sealing continues based on current trend. Moreover, for each scenario, stormwater runoff has been determined using the Soil Conservation Service curve number method. Results show that the implemented mitigation strategies allow achieving improved thermal comfort conditions and at the same time they can reduce runoff.