The significance of the soil surface moisture (&thgr;s) with respect to daily bare soil evaporation (Ed) 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 &thgr;s does not allow an accurate estimate of the ratio of Ed to the daily potential evaporation (Epd). Added variables such as Epd and the wind velocity are necessary to improve the prediction of the Ed/Epd ratio. In a second attempt, a simple model of Ed is proposed. It is based on three empirical parameters and required the measurement of &thgr;s obtained at midday, Epd, and the daily wind velocity. For a given soil, a single set of the three parameters allows an accurate estimate of Ed under soil moisture and climatic conditions encountered through the year in temperature areas. ¿ American Geophysical Union 1993