Effective Soil Hydraulic Properties for Heterogeneous Fields.

Unsaturated zone is important for calculations of water budget and land-atmosphere interactions in terms of partitioning upward and downward water fluxes at the land surface. Soil hydraulic properties show a large degree of spatial variation. Hydraulic properties (parameters) of the unsaturated zone at a spatial resolution typically larger than one square km are key inputs for land-atmosphere feedback schemes in soil-vegetation-atmosphere transfer (SVAT) models. The main idea is whether the interested process behavior in heterogeneous soils can be captured by a process that assumes only one set of soil parameters, such that the heterogeneous system is replaced by an equivalent homogeneous system. This study derives effective hydraulic properties under transient flow conditions. We investigate: 1) how the flow boundary conditions control the averaging scheme; 2) how the spatial variation of soil hydraulic parameters controls the effective parameters of larger scale soils. 3) How effective parameters are sensitive to different hydrological processes. Using randomly generated hydraulic parameters data, we will consider various processes such as precipitation, evaporation, and root water uptake. Inverse procedure is used to determine the effective hydraulic parameters for various flow scenarios.