Abstract:

Daily temperature oscillations can cause fluctuations in the amount of water retained in a soil. These fluctuations can be measured by high precision weighing lysimeters. We analyzed the data of a lysimeter in a sandy dune sediment in Southern Spain by means of unsaturated thermo-hydraulic numerical models which considers water, vapor and heat transport in the soil as well as soil-atmosphere interactions such as precipitation, evaporation and solar radiation. The analysis shows that daily temperature oscillations, psychrometrics and soil water retention can explain the fluctuations of the amount of liquid water in the soil. The retention curve, especially its driest part, is essential for the existence of these fluctuations. The fluctuations could not be reproduced by a model using the van Genuchten retention curve with a constant residual saturation. On the other hand, satisfactory results could be obtained by models using retention curves that at their driest part still show a change of saturation with suction. Moreover, the models suggest within the top few decimeters of the soil a pattern of alternating bands of condensation and evaporation, which follows the daily temperature oscillations that fade out deeper in the soil.