Assessing the hydrological performance of a modular blue roof over time

Blue roofs are lightweight and low-cost sustainable urban drainage systems, which can help control stormwater runoff from building rooftops. Most of the results in the literature concerning the hydrological behaviour of blue roofs rely on a limited number of rainfall events observed over a short monitoring period. This leaves open the research question of how these systems perform over time. This paper presents the results of a six-year monitoring campaign of a full-scale pilot of a modular blue roof installed in Catania, southern Italy. The retention and detention performance of the system is evaluated over time with reference to 52 precipitation events from all seasons of the year that occurred between 2018 and 2024. The modular blue roof showed average retention and detention efficiencies of 44% and 71%, respectively, in the monitored period. Comparison of the system performance year by year revealed that no significant trends in the retention and detention efficiency can be observed, thus showing persistency in the hydrological benefits of the system despite the poor maintenance activity carried out in the installation.