Simulating annual runoff retention performance of extensive green roofs: A comparison of four climatic regions in China

Abstract

The hydrologic performance of green roofs can be notably influenced by local climatic conditions. The majority of studies have focused on event-based retention performance of particular green roof configuration and climatic condition, making it difficult to predict green roof retention and formulate an efficient green roof configuration in a new location. To date, limited studies have assessed and compared annual or long-term runoff retention performance of green roofs in different climatic regions, and the impacts of climatic conditions on reduction effectiveness of green roofs remain unclear. In this study, a water balance model of green roofs coupling evapotranspiration rate estimation was developed to simulated the annual retention performance of green roofs. Four cities located in different climatic regions of China were selected to compare their average annual and seasonal runoff retention performances of extensive green roofs using 11 years of meteorological data, and assess the impacts of substrate storage capacity, vegetation types parameters and rainfall patterns on runoff retention performance among climatic regions. Results showed that average annual runoff retention in the dry continental climate of Lanzhou was 73.8%, which was higher than that in the humid climatic regions of Beijing (48.9%), Chongqing (45.2%) and Shenzhen (30.0%). Average runoff retention performance of extensive green roofs was the highest in spring for Beijing and Lanzhou, and in winter for Chongqing and Shenzhen. In Lanzhou and Beijing, the enhancement of increases in substrate water storage capacity on runoff retention was higher; and in Chongqing and Shenzhen, the impact for increases in crop coefficients (i.e. higher water use plants) was more efficient. Runoff retention performances of extensive green roofs were significantly decreased as rainfall depth increased. Longer antecedent dry weather period significantly lowered antecedent substrate moisture and resulted in higher runoff retention performances of extensive green roofs. These results can assist to formulate an efficient green roof configuration in local climatic condition and spatially allocate appropriate sites to optimize retention performance of green roofs.