Simulation and Measurement of Evaporation from a Bare Soil

A numerical model was used to simulate evaporation, water, and temperature profiles for a bare soil over drying cycles of 8, 9, and 20 d using soil hydraulic characteristics and meteorological data as input. The model was also used to evaluate the effect of the thickness of the surface layer in the model on the simulated evaporation rates. The simulated values were compared to actual measurements made over the same period of time. The model predicted cumulative evaporation within 1 standard deviation (SD) of the measured values, and in 34 of 37 cases, predicted daily rates also within 1 SD of the measured means. The predicted water and temperature profiles were within 1 SD of the means measured. The accuracy of the model was further confirmed by its ability to predict soil surface temperature within 1.0°C and net radiation within 40 W/m 2 of the measured values. The sensitivity of the simulated evaporation rates to the assigned thickness of the surface layer suggested that a value of 0.005 m was adequate under the conditions in which the model was tested. Hence, we conclude that the model is accurate to predict bare soil evaporation rates, as well as soil water and temperature profiles.