Green roofs in the humid subtropics: The role of environmental and design factors on stormwater retention and peak reduction.

Numerous factors affecting the hydrological performance of green roofs vary by climate and region. But meteorological factors have received relatively little attention, while no empirical research has focused on a quantified assessment of design and environmental factors on retention and peak reduction in humid subtropical climates. In this study, the hydrological performance of green roofs with designed substrates and vegetation was monitored in a humid subtropical climate. The influence of design and environmental factors was quantitatively assessed by ANOVA and regression. Results showed that substrates based on shale and perlite performed best in combination with grasses or forbs. The order of factors influencing retention was rainfall depth > relative humidity > substrate > antecedent volumetric water content > mean intensity. As for peak reduction, the order was rainfall depth > substrate > mean intensity. These findings suggest that the role of design factors is limited compared to environmental factors. However, the peak reduction or retention of runoff on a green roof can still be improved by adjusting the materials and relative proportions of the substrates. The key factors and optimal design features identified in this study may help promote the application of green roofs in humid subtropics.