Summer Thermal Performance and Water Management Efficiency of Blue Green Roof System: Insights from a Comprehensive Monitoring Campaign

Rising water scarcity and climate change pressures have prompted the EU to push for net-zero water consumption; however, cities struggle with the impact of extreme rainfall events. Adopting sustainable water management strategies is necessary to address the pressing challenges. With roofs covering approximately 20% of urban areas, Blue Green Roofs (BGR) are essential for water harvesting, reducing drainage loads, and enabling water reuse. In this con-text, this study aims to: (i) assess the summer thermal performance of two com-mercial BGRs—intensive and extensive—with diverse plant species through the analysis of intralayer temperature variations, and (ii) evaluate the water retention potential of the BGRs under an extreme rainfall event. A monitoring campaign was conducted on two BGR test fields in San Donà di Piave, a flood-prone city in northern Italy. Intralayer temperatures and water levels in the water storage layer have been monitored through sensors providing a high-resolution dataset. Among the plant species tested, Sedum, common in extensive GRs, demonstrated lower intralayer temperatures than lawns used in intensive green roofs. Both BGR systems exhibited a peak attenuation of approximately 9 °C of ambient air temper-ature during the hottest day of August 2021. This study provides valuable insights into BGR technology by comparing the thermal performance of different plant types, considering the contribution of a filled water storage layer, and evaluating its effectiveness in stormwater retention during an extreme rainfall event, thereby underscoring its potential to enhance urban environments.