Author(s): F. Rodolfo Reyes; Sergio Vera; Felipe Victorero; Waldo Bustamante; Jorge Gironás; Victoria Rojas; Carlos A. Bonilla
Linked Author(s): Jorge Gironás L.
Keywords: Sustainability; Semiarid climate; Green roofs; Soil water availability; Sedum spp
Abstract: Most green roofs have been studied and built in humid climates, with many benefits such as thermal isolation and biodiversity. However, little is known about their performance in arid and semiarid climates where irrigation system affects the sustainability of this technology. In order to improve the water efficiency and get a sustainable water management, five 4-m2 modules of vegetated roofs were instrumented and monitored to evaluate the irrigation water requirements during the first yea r in Santiago, Chile (33°26’S, 70°39’W, 570 MASL) .Based on the water retention properties, the maximum soil available water was 10%, the permanent wilting point was 17%and 27%at field capacity. Three substrate depths (5-cm, 10-cm and 20-cm) and three commercial drainage systems found in Chile were evaluated. The results showed that with the same drainage system and irrigation conditions, the substrate depth controls both, stored water and daily temperature oscillation during summer. While 5 and 10-cm substrates showed low water contents (close to the minimum for plant survival) and peak temperatures (54°C and 38°C respectively) ,20-cm substrate reached the minimum soil moisture only in days with high atmospheric demands reaching a peak soil temperature of 27°C. To provide a better and sustainable condition for the 5-cm green roof modules, water retention capacity was incremented to resist the harsh summer atmospheric conditions. With a proper drainage system, substrate moisture in 5-cm green roof was equal or higher than the measured in the 20-cm green roof. However, peak temperatures were not reduced. Therefore, in addition to water requirements and plant species tolerance to drought and high temperatures, it is crucial to know the soil water retention properties and selecting a suitable type of drainage. These factors, along with the irrigation criterion, must be considered in order to get a sustainable water management on an urban green roof when built in semiarid climate.