Evaluating the stormwater reduction of a green roof under different rainfall events and antecedent water contents with a modified hydrological model

This study simplifies the recession process, includes the hourly evapotranspiration, and modifies the surface layer of green-roof hydrological model based on the existing Green–Ampt method and Curve Number (CN) method usually applied for event-total runoff. The results show that the proposed model improves the predicting accuracy of the outflow, CN method performs as prominent as Green–Ampt method but more efficient, and the model performs well for rainfall events with different intensities, duration, and hyetograph. Based on observation, the retained volume and peak reduction are close to 50% on average with a 1-to-2-hour peak delay. The results of three-year simulation show that the retained volume and peak reduction reach 50% for 75% of the events when AWC is 30%. Almost all rainfall is retained for events with rainfall amounts smaller than 20 mm when AWC is smaller than 30%, while 50% (60%) rainfall (peak) is retained (reduced) for events larger than 20 mm when AWC is smaller than 20%. with the model verified using various rainfall events, the study generalizes an equation to estimate the rainwater retained by green roofs and concludes quantitatively with the stormwater-detention performance of a green roof in general under different AWC to assist the decision-making of irrigation concerning the goal of stormwater detention.