Green roof evapotranspiration rates and stormwater control under subtropical climate: a case study in Brazil

Abstract

In this study a long-term field experiment evaluating evapotranspiration rates from irrigated and non-irrigated green roof modules, as well their impacts on stormwater control was accomplished. Six green roof modules (3 irrigated and 3 non-irrigated) vegetated with S. rupestre were monitored throughout 8 months in southern Brazil. Four non-vegetated modules (2 irrigated and 2 non-irrigated) were simultaneously assessed to understand the role of the vegetation in the whole process. The average evapotranspiration under water-stress (ETr) was 2.6 mm.day-1, while mean evapotranspiration under water-abundance (ETp) was 2.8 mm.day-1. Higher evapotranspiration rates were observed during summer, increasing the substrate storage capacity, although ETr amount along the seasons was very similar, mainly affected by climatic conditions. The long-term analysis showed that 47% of the total rainfall was converted into runoff, 21% was retained in the green roof modules and 32% was released through evapotranspiration, reinforcing the importance of vegetation as a mechanism for improving stormwater control benefits. The results of this research also allowed the establishment of a crop coefficient (Kc) time series, with a monthly average of 0.9 which permits the S. rupestre evapotranspiration to be preliminarily estimated by using equations developed for reference culture without the need of monitoring.

Unmanaged Vegetated Roofs Hydrological Performance in Subtropical Areas:An Investigation in São Paulo, Brazil

“…Recent studies in tropical and subtropical regions of Brazil are scarce and mainly use small scale laboratory models and adopt succulent or grass plants in their research, but demonstrate a relevant capacity of VR water management in this geographical region . Arboit et al (2021) used small scale models to evaluate the evapotranspiration and runoff rates in a subtropical climate of Brazil. Results for runoff demonstrate that the species used, Sedum rupestre, did not provide better water retention performances than a roof module without any vegetation.…”