Simulation of Salt Cedar Evapo-Transpiration

The use of the Penman equation, as modified by Van Bavel and Monteith, for simulating evapotranspiration from dry plant surfaces requires prior knowledge of the surface albedo, surface roughness height and stomatal resistance. These variables were determined for salt cedar using measured values of salt cedar evapotranspiration. It was found that the equation was insensitive to variations in albedo so that values normally ascribed to vegetated surfaces could be used. The surface roughness height for salt cedar, 10 ft (305 cm) to 13 ft (396 cm) in height, was found to be 37 cm. The relative insensitivity of the equation to small variations in surface roughness height allowed for deviations of 10 cm to 15 cm without appreciable error. Stomatal resistance was found to vary seasonally from 0.3 sec per cm to over 5 sec per cm and to be indirectly related to temperature and directly related to wind speed. Stomatal resistance was found to be related to water depth only during seasons when the plants were inactive.