Evapotranspiration Rates from Extensive Green Roof Plant Species

Abstract

Green roofs have been shown to reduce the stormwater runoff from buildings. In order tomodel the reduced stormwater effect of green roofs, reliable estimates of ET from the CAM plants isrequired. Greenhouse controlled environmental conditions were used to measure and predict ETfrom CAM plants during winter and fall/spring regimes, along with climatic parameters including airtemperature, wind speed, radiation and humidity during 21-day periods without rain. The plantedboxes evapotranspired 28% and 57% more water to the atmosphere than was evaporated from theunplanted boxes for the winter and spring/fall, respectively. ET for a green roof with CAM plantsaveraged 0.61 mm/d and 1.12 mm/d for each dry day during the winter and spring/fall season,respectively. The original Penman equation and Penman-Monteith ET models explained theobserved ET rates very well with crop coefficients of 0.74 in winter and 1.97 in fall/spring.