Stormwater retention capacity of blue-green roofs with various configurations: Observational data and modelling

Although dynamic changes in stormwater retention capacity (SRC) determine overall stormwater retention performance of blue-green roofs, few previous studies have investigated the dynamic changes of SRC of bluegreen roofs with various configurations. In this research, an experiment was designed to observe hydrological processes of blue-green roofs in Beijing. Based on the water balance theory, a conceptual hydrological model was developed by integrating a modified FAO-56 Penman-Monteith model, an AET formula with a water stress coefficient and Dalton's equation. Then the proposed model was validated using experimental data. Results show that the model can simulate the SRC dynamics well, with the Nash-Sutcliffe and determination coefficients both exceeding 0.6. The consumption and recovery of the SRC in blue-green roofs are mainly driven by rainfall and actual evapotranspiration, respectively. As actual evapotranspiration decreases with seasonal changes, the fluctuation amplitude of SRC in blue-green roofs diminishes, ranging from 32.53 mm to 11.34 mm. Although increasing the depth of substrate and storage layers is able to enhance the SRC of blue-green roofs, there are optimal upper limits for these depth because of regional climate conditions. In Beijing, the optimal upper limits for substrate and storage layer depths are 300 and 30 mm, respectively. This information can assist designers in evaluating the cost-effectiveness of design choices for blue-green roofs. The developed model serves as an effective tool for simulating SRC and is expected to aid in the design of blue-green roofs.