Effective Soil Hydraulic Properties for Infiltration and Redistribution in Unsaturated Zone

The fundamental soil hydraulic properties that control hydrologic processes are the soil water potential and the hydraulic conductivity as functions of soil water content. Average/effective soil hydraulic properties are essential for many large scale hydrological, environmental or climate studies. In this study, we investigate 1) how the hydrologic processes impact on the effective hydraulic properties; 2) how the effective hydraulic property schemes are sensitive to the initial and boundary conditions; and 3) how the effective hydraulic properties evolve for different hydrologic processes. The main idea is whether the important process behavior in heterogeneous soils can be captured by a process that assumes one set of soil parameters, such that the heterogeneous system is replaced by an equivalent homogeneous system. By using field and re-generated hydraulic data sets, we derive effective hydraulic properties under transient flow conditions. Precipitation, infiltration, evaporation, and redistribution and their effects on the effective hydraulic properties are considered. In particular, we investigate the concepts of using both constant and time-dependent effective hydraulic properties and explore the conditions under which the constant effective hydraulic properties are feasible in large scale hydro-climate simulations.