Experimental study on the stomatal resistance of green roof vegetation of semiarid climates for building energy simulations

Abstract

Current modelling approaches for energy simulations in green roofs use a range of values for parameters such as stomatal resistance (rs) of the vegetation. rs reflects the capability of a plant to transpire, thus it has a direct relation to the cooling potential of green roofs in buildings. Therefore, rs values need to be revised based on differences among species and contrasting environmental conditions, considering anatomical and physiological characteristics among species and their changes throughout the day. In order to provide real data on species commonly used for green roofs in semiarid climates, this paper aims to evaluate the stomatal resistance of nine species of groundcovers and to compare this data with current models. rs was measured for each species at 8:00 h, 12:00 h, 16:00 h and 20:00 h during day and nighttime in winter in a leaf located at the middle of the stem. The results of this study showed that rs varies significantly among species, throughout the day and between the side of the leaf (adaxial or abaxial). The lowest rs values for species was at noon ranging from 264 to 807 s m- 1 and the highest rs was at night ranging from 568 to 973 s m-1. Sedum spurium red, Sedum hybrid, and white and pink Verbena sp. had the largest rs variation in the day-night cycle. The results of rs are higher than those values recommended for some energy simulation models.