Estimating Effective Soil Hydraulic Properties of Heterogeneous Soils Using near-Surface Soil Moisture Assimilation Scheme.

Using Ines and Mohanty (2008) near surface (0-5 cm) soil-moisture assimilation scheme, this paper quantifies the effective soil hydraulic parameters of the root zone (0-200 cm) under various scenarios of vegetation type, bottom boundary condition, and soil layering. Genetic algorithm was used to identify simultaneously the soil hydraulic functions (soil water retention q(h) and hydraulic conductivity K(h)) in the soil profile by inverting governing flow equation. In this comparison study, we considered three hydrologic cases i) Case 1: homogeneous free-draining column, ii) Case 2: homogeneous column with a shallow water table (100, 150 and 200 cm), iii) Case 3: heterogeneous column with different combinations of soil textural layering. To reflect a variety of soil layers in real world situations, 6 combinations of sand, silt and clay loam soils in the soil profile were used for Case 3. The uncertainties of the estimated soil hydraulic parameters were evaluated in the genetic search. For the purpose of validation, the near-surface soil moisture assimilation scheme was applied to several field sites in the Little Washita watershed, Oklahoma. We envisaged that our findings will help in the estimations of pixel-based effective soil hydraulic parameters for land surface models under heterogeneous soil, vegetation, and ground water conditions.