Characterization of watershed scale soil moisture variability in structured soils

Soil moisture is an important component in many hydrologic and land-atmosphere interactions. Proper characterization of soil moisture variability is vital for understanding hydrological, ecological and biogeochemical processes. At watershed scale, root zone soil moisture variability could effectively be described by studying the spatial variability in soil hydraulic parameters (SHPs). In this study, we analyzed the behavior of soil moisture variability within the Little Washita watershed, Oklahoma by using the multi-step outflow experimental data from soil cores collected during the Southern Great Plains (SGP) 1997 hydrology experiment [Mohanty et al. 2002]. SHPs were calculated using inverse modeling and these properties were used to calculate distributed soil moisture values across the watershed using forward modeling. In calculating SHPs we took into account effects of non-equilibrium and preferential flow in vadose zone and compared several conceptual water flow models in structured porous media. We have demonstrated how soil moisture variability is dependent on different water flow processes and as a consequence varies with different models. The range of mean moisture contents observed in these samples was from moderately wet to dry conditions in different parts of the watershed and this soil variability is captured by different models. Soil moisture is correlated with soil properties and these observed spatial patterns affect the components of water balance.