Development of a Simulation Model for Estimation of Potential Recharge in a Semi-arid Foothill Region

The SMPR (Soil Moisture and Potential Recharge) model is developed to simulate soil moisture content and potential recharge under semi-arid conditions. In SMPR model, infiltration and soil moisture redistribution follow two successive stages. In stage (I), precipitation infiltrates and is distributed into the soil profile utilizing the soil moisture accounting fashion and in stage (II), moisture is redistributed using simplified Richards’ equation (neglecting matric-potential gradient). Liquid and vapor evaporation from bare soil are estimated based on Dual-Crop methodology [Ke and optimized Kcb (0.17)]. Two commonly applied unsaturated hydraulic conductivity functions [K(θ)] of B-C (Brooks and Corey) and V-G (van-Genuchten); and an Empirical Exponential (E-E) equation are locally calibrated and used for potential recharge estimation (as main simulation objective). Model performance (calibration/validation) is based on reasonable estimation of potential recharge and acceptable simulation of soil moisture, considering local lysimeter data. According to results, B-C, V-G an E-E equations produced acceptable simulation of soil moisture content (NRMSE < 30%), however, potential recharge was underestimated/overestimated, using K(θ) by B-C/V-G. The best estimation of potential recharge (based on absolute annual recharge error, ∆Q < 10%) was achieved by the SMPR model with K(θ) of E-E. Results of the relative simple SMPR model [K(θ) by E-E equation] compared favorably with HYDRUS-1D sophisticated model [using locally calibrated V-G equation of K(θ)].The proposed SMPR model requiring minimal data, can be used in regions with limited data.