Management strategies for maximizing the ecohydrological benefits of multilayer blue-green roofs in mediterranean urban areas.

Multilayer Blue-Green Roofs are powerful nature-based solutions that can contribute to the creation of smart and resilient cities. These tools combine the retention capacity of traditional green roofs with the water storage of a rainwater harvesting tank. The additional storage layer enables to accumulate the rainwater percolating from the soil layer, that, if properly treated, can be reused for domestic purposes. Here, we explore the behavior of a Multilayer Blue-Green Roof prototype installed in Cagliari (Italy) in 2019, that have been equipped with a remotely controlled gate to regulate the storage capacity of the system. The gate installation allows to manage the Multilayer Blue-Green Roof in order to increase the flood mitigation capacity, minimizing the water stress for vegetation and limiting the roof load with adequate management practices. In this work, 10 rules for the management of the Multilayer Blue-Green Roof gate have been investigated and their performances in achieving different management goals (i.e., mitigating urban flood, increasing water storage and limiting roof load on the building) have been evaluated, with the aim to identify the most efficient approach to maximize the benefits of this nature based solution. An ecohydrological model have been calibrated based on field measurements carried out for 6 months. The model has been used to simulate the system performance in achieving the proposed goals, using as input nowdays and future rainfall and temperature time series. The analysis reveled the importance of the correct management of the gate, highthing how choosing and applying a specific management rule helps increasing the performance in reaching the desired goal.