Since the direct measurement of soil hydraulic conductivity [Kw(θ)] is time consuming and difficult, several methods have been suggested for its prediction. However, their application still requires some kind of direct or experimental measurement, even after calibration. Considering much easier measurement of the air permeability [Ka(θ)] and the water and air flows in the soil medium, several attempts have been made to link Kw(θ) and Ka(θ), most of which have used Ka(θ) to predict the saturated hydraulic conductivity (Ks). The current research was aimed to model the air permeability and evaluate its application for Kw(θ) prediction. In this regard, laboratory measurements were conducted for Kw(θ) and Ka(θ) at different soil moisture contents (θ). Then, we introduced a semitheoretical model and evaluated it using measured data. Results showed that the proposed model can predict Kw(θ), with an average evaluation error of 3.69% and average R2 of 0.88. Regarding the fast and nondestructive measurement of Ka(θ) compared with Kw(θ), the proposed model seems to be more practical to characterize unsaturated soil hydraulic conductivity and can improve the accuracy and efficiency of Kw(θ) estimation.
