Experimental Analyses of the Evaporation Dynamics in Bare Soils under Natural Conditions

In spite of recent progresses in evaporation estimate through advanced models and laboratory experiments, the drying process of bare soils through its successive stages remains difficult to predict. A study which addresses evaporation modeling in natural bare soils is presented. It relies upon hydro-meteorological measurements performed in a plot with a bare silt loam soil maintained in natural conditions. The following steps are involved: estimate of daily actual evaporation, Ea, through the hydrological balance, scaling with pan evaporation measurements, Epan, and analysis of the relation of Ea/Epan with the soil moisture vertical profile. The results enable us (1) to check the occurrence of the first stage of the evaporation process, characterized by not limited-soil water supply and high evaporative rates, and (2) to identify the transition from the first to the second stage, with decreasing soil water-limited Ea values. The last point requires the introduction of a soil water content threshold at 5 cm depth, that is associated with the soil field capacity. The adopted procedure provides insights on the soil water dynamics at depths differently involved through the successive stages of the evaporative process. Finally, indications on the use of pan evaporation measurements in evaporative rate estimate at least during the first stage of the process are also given.