Advances in Soil Evaporation Physics—A Review

Abstract

Globally, evaporation consumes about 25% of solar energy input and is a key hydrologic driver with 60% of terrestrial precipitation returning to the atmosphere via evapotranspiration. Quantifying evaporation is important for assessing changes in hydrologic reservoirs and surface energy balance and for many industrial and engineering applications. Evaporation dynamics from porous media reflect interactions between internal liquid and vapor transport, energy input for phase change, and mass transfer across air boundary layer. We reviewed recent advances on resolving interactions between soil intrinsic properties and evaporation dynamics with emphasis on the roles of capillarity and wettability affecting liquid phase continuity and capillary driving forces that sustain Stage I evaporation. We show that soil water characteristics contain information for predicting the drying front depth and mass loss at the end of Stage I and thus derive predictions for regional‐scale evaporative water losses from soil textural maps. We discuss the formation of secondary drying front at the onset of Stage II evaporation and subsequent diffusion‐controlled dynamics. An important aspect for remote sensing and modeling involves nonlinear interactions between wet evaporating surfaces and air boundary layer above (evaporation rate is not proportional to surface water content). Using pore scale models of evaporating surfaces and vapor transport across air boundary layer, we examined the necessary conditions for maintenance of nearly constant evaporation while the surface gradually dries and the drying front recedes into the soil. These new insights could be used to improve boundary conditions for models that are based on surface water content to quantify evaporation rates.

Pore-scale modeling of phase change in porous media

“…Our model can be extended to three dimensions, where the hydrodynamics in the bulk fluid are described by the Navier-Stokes equations. This three-dimensional description will allow us to compare the dynamics of interfacial jumps with direct observations at the pore scale [78,[116][117][118][119] and evaporation rates in porous media at the macroscopic scale [120,121]. …”

Water ages in the critical zone of long-term experimental sites in northern latitudes

“…Root water uptake was limited according to rooting depth observations to the upper 15 cm at the heather site in Bruntland Burn and to the entire 50 cm soil profile at the forested sites. Soil evaporation (E) was limited to the upper 10 cm based on experiments by Or et al (2013). ET was partitioned into potential E and potential transpiration (T ) according to the canopy coverage (Table 1) according to Ritchie (1972).…”

Column-scale unsaturated hydraulic conductivity estimates in coarse-textured homogeneous and layered soils derived under steady-state evaporation from a water table

“…One-dimensional steady-state evaporation from a fixed shallow water table (WT) is dependent on the WT depth and on the soil hydraulic properties Shokri and Salvucci, 2011;Assouline et al, 2013;Or et al, 2013). Two distinct scenarios are often considered; the first when the WT is shallow enough for the soil to sustain hydraulic continuity between the WT and the surface due to capillary forces, and the second when the WT reaches a critical depth (denoted as D max ) below which the hydraulic continuity between the WT and soil surface is no longer maintained.…”