Heat and water transport in soils and across the soil-atmosphere interface: 2. Numerical analysis

In an accompanying paper, we presented an overview of a wide variety of modeling concepts, varying in complexity, used to describe evaporation from soil. Using theoretical analyses, we explained the simplifications and parameterizations in the different approaches. In this paper, we numerically evaluate the consequences of these simplifications and parameterizations. Two sets of simulations were performed. The first set investigates lateral variations in vertical fluxes, which emerge from both homogeneous and heterogeneous porous media, and their importance to capturing evaporation behavior. When evaporation decreases from parts of the heterogeneous soil surface, lateral flow and transport processes in the free flow and in the porous medium generate feedbacks that enhance evaporation from wet surface areas. In the second set of simulations, we assume that the vertical fluxes do not vary considerably in the simulation domain and represent the system using one-dimensional models which also consider dynamic forcing of the evaporation process, for example, due to diurnal variations in net radiation. Simulated evaporation fluxes subjected to dynamic forcing differed considerably between model concepts depending on how vapor transport in the air phase and the interaction at the interface between the free flow and porous medium were represented or parameterized. However, simulated cumulative evaporation losses from initially wet soil profiles were very similar between model concepts and mainly controlled by the desorptivity, Sevap, of the porous medium, which depends mainly on the liquid flow properties of the porous medium

Heat and Water Transport in Soils and across the Soil-Atmosphere Interface: Comparison of Model Concepts.

Evaporation from the soil surface represents a water flow and transport process in a porous medium that is coupled with a free air flow and with heat fluxes in the system. We give an overview of different model concepts that are used to describe this process. These range from non-isothermal two-phase flow two-component transport in the porous medium that is coupled with one-phase flow two-component transport in the free air to isothermal water flow in the porous with upper boundary conditions defined by a potential evaporation flux when available energy and transfer to the free air flow are limiting or by a critical threshold water pressure when soil water availability is limiting. The latter approach corresponds with the classical Richards equation with mixed boundary conditions. We formulated the different equations and identified assumptions behind simplified forms. Conditions for which lateral and up and downward air flow in the porous medium and vapor diffusion in the pore space play an important role were identified using simulations for a set of scenarios. When comparing cumulative evaporation fluxes from initially wet soil profiles, only small differences between the different models were found. The effect of vapor flow in the porous medium on cumulative evaporation could be evaluated using the desorptivity, Sevap, which represents a weighted average of liquid and vapor diffusivity over the range of soil water contents between the soil surface water content and the initial soil water content. Vapor flow influences the shape of the moisture front close to the soil surface. Simulated evaporation fluxes under dynamic forcing, e.g. due to diurnal variations in net radiation, differed considerably between the models. Experimental methods that allow monitoring of diurnal evaporation fluxes are therefore essential for model discrimination and parameterization

Conceptualization of contamination using depth discrete monitoring of dynamic PCE concentration changes during pumping

Raw data for individual queens used in the study. The first worksheet contains the main experiment, and the second has the survival analysis