Seasonal Variation in Recovery Process of Rainwater Retention Capacity for Green Roofs

Abstract

Highlights: The recovery process of the retention capacity is described using an exponential decline curve. The recovery rate is represented by the half-life of the water content after a storm (T50), and T50 varies with the seasonal variations in the weather conditions and vegetation coverage. During the wet season, T50 affects the rainwater retention performance of green roofs; during the dry season, the actual retention capacity, rather than T50, affects the performance. Green roofs need to quickly recover their water retention capacity between rainfall events to maintain their rainwater retention performance. In this study, the authors observed the rainwater retention, recovery process, and plant eco-physiological performance of green roofs with four local vegetation species under a typical subtropical monsoon climate for two years. The half-life of the water content after each rainfall (T50) was used to describe the recovery rate. The results indicate that (1) the decline in the water content after rainfall can be well described by an exponential decline curve (R2 > 0.7), and the average T50 of green roofs with Plectranthus prostratus Gürke was the shortest among the four plants; (2) the T50 in the wet season was significantly shorter than that in the dry season (p < 0.01) because of the seasonal variations in the weather conditions and eco-physiological activity, such as vegetation coverage and transpiration; (3) the rainwater retention of green roofs for rainfall events in the wet season was significantly lower than that in the dry season due to a relatively short antecedent dry period; (4) plants with a high maximum photosynthetic capacity, a strong root system, drought resistance, and large vegetation coverage were recommended as green roof plants. Above all, P. prostrates was found to be the best choice in the study.