Internal evaporation and condensation characteristics in the shallow soil layer of an oasis

Abstract

The surface energy balance was analyzed using observations from the Jinta oasis experiment in the summer of 2005. A negative imbalance energy flux was found during daytime that could not be attributed to the soil heat storage process. Rather, the imbalance was related to the evaporation within the soil. The soil heat storage rate and the soil moisture variability always showed similar variations at a depth of 0.05 m between 0800 and 1000 (local standard time), while the observed imbalanced energy flux was very small, which implied that water vapor condensation occurred within the soil. Therefore, the distillation in shallow soil can be derived using reliable surface energy flux observations. In order to show that the importance of internal evaporation and condensation in the shallow soil layer, the soil temperatures at the depths of 0.05, 0.10, and 0.20 m were reproduced using a onedimensional thermal diffusion equation, with the observed soil temperature at the surface and at 0.40 m as the boundary conditions. It was found that the simulated soil temperature improves substantially in the shallow layer when the water distillation is added as a sink/source term, even after the soil effective thermal conductivity has been optimized. This result demonstrates that the process of water distillation may be a dominant cause of both the temperature and moisture variability in the shallow soil layer.

Effect of vapour transport on soil evaporation under different soil textures and water table depths in an arid area of Northwest China

“…The amount of vapour condensation could account for 10%–37% of precipitation (Evenari, 1981; Hao et al, 2012; Jia et al, 2014; Kidron et al, 2000; Malek et al, 1999; Subramaniam & Kesava Rao, 1983). It increases soil water content and offers an available water source for plant utilization in the dry environment (Ao et al, 2016; Gowing et al, 2006; Gran et al, 2011; Milly, 1996; Sakai et al, 2009; Scanlon, 1992; Scanlon & Milly, 1994). In such environment, a high AE does not appear at noon when the temperature is high while a high AE occurs in the early morning from 7:00 to 9:00 a.m. when the topsoil is wetting and air temperature gets rising.…”