Green Roofs in Dry Cities. Selection of Plant Species According to Their Biological and Thermal Behaviour

Abstract This paper proposes the identification of adapted plant species with high local availability feasible for implementation as green roofs in dry cities. To this end, two experiments were conducted under controlled conditions. One of them aimed at determining the biological behaviour of a sample set of fourteen species based on the measurement of three variables: plant cover, water consumption, and leaf temperature. The other test sought to determine the thermal behaviour of green roofs by comparing preselected species according to their biological response with traditional roofs. In this case, the following meteorological variables were recorded: outdoor and indoor air temperature, substrate temperature, and water content. Finally, the data obtained were statistically processed. Biological results show that the species Aptenia cordifolia, Cynodon dactylon, Hyalis argentea, and Nassella tenuissima reach plant cover higher than 70% with Aptenia cordifolia recording the lowest water consumption, 217 l/year. Regarding thermal behaviour, the green roof with Nassella tenuissima -a shrubby native species- results in the highest mitigation of outdoor temperature, reducing average indoor temperature by 3.4°C. These results show the biological and thermal fitness of local species that guarantee the sustainability of the system itself as well as higher thermal efficiency with lower water consumption.