Significance of soil surface moisture with respect to daily bare soil evaporation

The significance of the soil surface moisture (θ s ) with respect to daily bare soil evaporation ( E d ) is analyzed using data from numerical simulations. This was performed by running a mechanistic model of heat and water flows in the soil. The mechanistic model was calibrated and validated on three different soils with contrasted hydraulic properties. Results show that θ s does not allow an accurate estimate of the ratio of E d to the daily potential evaporation (Ep d ). Added variables such as Ep d and the wind velocity are necessary to improve the prediction of the E d /Ep d ratio. In a second attempt, a simple model of E d is proposed. It is based on three empirical parameters and required the measurement of θ s obtained at midday, Ep d , and the daily wind velocity. For a given soil, a single set of the three parameters allows an accurate estimate of E d under soil moisture and climatic conditions encountered through the year in temperate areas.