Mixture of time scales in evaporation: Desorption and self-similarity of energy fluxes

The time evolution of evaporation from a bare soil, over a 9-d period follo wing irrigation, is described by a combination of daily and hourly drying p atterns. From the second day, the daily evaporation shows a second stage of drying that can be described as a desorptive process (evaporation proporti onal to (t - t(0))(-1/2), where t is time in days and t(0) is the day when the second stage starts). The short time (hourly) evaporation rate can be m odeled on the basis of a type of self-similarity in the energy balance comp onents. Combining the evaporative flux behavior at the two time stales, des orption at the daily timescale and self-similarity for the diurnal variatio ns, a robust description of evaporation for drying land surfaces is obtaine d. This approach is tested using accurate measurements of the different com ponents of the energy balance at the soil surface, obtained at 20-min inter vals. The model accurately describes the time evolution of the evaporative flux and could be used for the disaggregation of daily or weekly evaporatio n into hourly values.