Modelling the hydrological response of blue-green roofs: ECO-PRO model.

Green roofs are climate-adaptive measures able to address many urban challenges like heat islands, water scarcity, floodings, pollution and biodiversity loss. Recently, the "blue-green roof" variant has gained attention for its enhanced functionality, since, incorporating a high-capacity storage layer, they can retain significant amount of rainwater. This last can be gradually released, reducing stress on urban drainage during heavy storms, sustain passive irrigation and provide greywater for reuse. Modelling green infrastructures is essential for optimizing design and efficacy, and, in this context, ecohydrological models, which capture the complex ecological and hydrological interactions, offer a valuable option. This study introduces the ECO-hydrological Polder Roof mOdel (ECO-PRO), a tailored ecohydrological model specifically for multilayer green roofs. ECO-PRO is a numerical model able to simulate dynamically the blue-green roofs hydrological response to climate conditions and management practices, estimating water flow and storage across layers. The model was implemented based on an experimental site in Palermo (Italy), using a high-resolution dataset and performing parameters optimization through genetic algorithms. Simulated water fluxes and time series of soil moisture and outflow generated by the system demonstrated strong alignment with observed data over a three-year monitoring period, with robust performance indicators. Notably, the coefficient of determination (R2) for daily runoff was 0.88. Parameter sensitivity and uncertainty assessments further validated the model's reliability. A test model application accurately captured stormwater retention after prolonged rainy spells (R2 = 0.91), confirming its effectiveness for the dynamic assessment of water volumes released and retained by the system.