Prediction of unsaturated soil hydraulic conductivity with electrical conductivity

Soil hydraulic conductivity ( K ) varies greatly with matric potential ( h ) and exhibits a high variability at the field scale. However, this key property for estimating water flux in soils is difficult to measure. In contrast, soil electrical conductivity ( σ ) is easier to measure and is influenced by the same parameters affecting K . We derive a simple relationship between σ and K ( h ) and test it against laboratory and literature data. Importantly, we show that parameters of this σ ‐ K ( h ) relationship can be completely determined with accessible measurements of saturated hydraulic conductivity, electrical conductivity of the soil solution, and clay content. This results in K ( h ) estimation with a RMSE ranging between 0.4 and 0.5 for log K , i.e., of the order of most experimental determinations of K . A further test of the σ ‐ K ( h ) relationship on the large UNSODA hydraulic database shows good agreement and the robustness of the relationship. Such a relation could be useful in the spatial monitoring of water fluxes at the field scale using electrical resistivity tomography if the σ ( h ) relationship can be obtained.