Soil Hydraulic Parameters for Moisture Redistribution In Heterogeneous Landscape.

Soil hydraulic properties at large model grid scales are often required inputs for many large-scale hydro-climate models. In this study, guidelines of effective hydraulic parameters are developed for simulating average infiltration and subsequent moisture redistribution over a heterogeneous field. Average large-scale infiltration and redistribution in heterogeneous soils are quantified through multiple simulations of local-scale processes, which are represented by a series of parallel columns. The effective hydraulic parameters are derived to simulate the average amount of water infiltrating into the soil and the subsequent surface soil moisture redistribution averaged over the large heterogeneous landscape. Simple hydraulic property aggregation schemes are developed where the effective value is derived only for one hydraulic parameter while keeping the other parameters at their arithmetic means. Results demonstrate that the effective hydraulic parameters typically exhibit a step change from infiltration to redistribution with the size of the step change being related to the degree of hydraulic parameter heterogeneity and the correlations among the hydraulic parameters. However, the effective hydraulic parameters do not change significantly over time for the moisture redistribution. This finding is particularly useful in practical applications in simulating large scale moisture redistribution given that relatively constant effective hydraulic parameters are adequate for predicting transient behavior of soil moisture redistribution.