Dynamics of the near-surface evaporation zone and corresponding effects on the surface energy balance of a drying bare soil

Despite a long history of application to bare soils drying by evaporation, the implications of the coupled heat and moisture transfer theory of Philip and de Vries for temperature and moisture regimes near the soil surface have not been fully described, either because grid resolutions used within the soil in numerical implementations were inadequate and/or research objectives were focussed elsewhere. In this paper, a finite-element numerical simulation of heat and moisture regimes using the original theory of Philip and de Vries is applied to a bare silt-loam soil drying during a 10-d rain-free period that occurred at the end of a 66-d field study at Agassiz, British Columbia. The unique aspect of the simulation is that the grid resolution is more than adequate to correctly determine the reported location, magnitude, and shape of the subsurface evaporation zone that develops during daytime for many of the days and corresponding effects on surface energy balance components and soil temperature and moisture.

Research highlights▶ Evaporation from a bare soil simulated with theory of Philip and de Vries (1957). ▶ Narrow subsurface evaporation zone develops daily when surface becomes dry enough. ▶ Subsurface evaporation implies more soil heat flux to supply required latent heat. ▶ Subsurface evaporation zone moves down and up most days due to drying and rewetting. ▶ Very fine grids near the soil surface required to simulate this behaviour correctly.