The strong spatial variability of the soil characteristics in the unsaturated zone has a significant impact on the distribution and transport process of the soil water. It should be particularly concerned in the Badain Jaran Desert, China, where the vadose zone has a huge thickness and is difficult to observe. Based on the collected data from soil water observations at different depths and measurements of the hydraulic parameters, the variability characteristics of the aeolian sands in the Badain Jaran Desert is analyzed with Monte-Carlo simulation by using the logarithmic normal distribution model and the cross-correlated model of the soil water retention characteristics. As indicated in the results, the volumetric content of movable water is less than 5\% in the downward infiltration zone. Accordingly, the vertical distribution of the soil water potential is reconstructed and the results indicate that the hydraulic gradient is approximately 1.0 in the downward infiltration zone, which basically satisfy the free infiltration condition under the force of gravity. Taking the residual water content as an independent random variable and using the Richards equation, the distributions of volumetric water content with respect to different infiltration rates are assessed with Monte-Carlo simulation. The reasonable variation range of the infiltration rate is determined from the comparison of statistical properties between simulated and observed data. Results show that the most possible range of the infiltration rate is 30-41 mm/a. The possibilities of infiltration rate values are very small for that are less than 10 mm/a or higher than 50 mm/a. Stochastic simulation of the vadose zone water provides a new perspective for the study of groundwater recharge in the Badain Jaran~Desert.
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