Modeling soil moisture responses under evaporative conditions

Based on the finite element method(FEM) and the modified integrated Richards equation model(IRE),the responses of soil moisture under the evaporative condition for 5 different soil types were numerically studied in this paper.Numerical experiments were carried out on the 100-cm high soil columns subject to a constant potential evaporation of 0.5 cm/d and free drainage from near saturation.The results show that the variations in vertical distributions of soil moisture content for the 5 soil types exhibit a single inflexion at about the depth of 20 cm,and the curvature in upper region is greater than that in lower region.The variation in soil moisture content is more rapid in the first 15 days than that in the late period.The three-phase theory for evaporation can thus be confirmed by the results.The cumulative evaporation and water loss at the lower boundary are highly related to the soil textures.Furthermore,the changes in the amount and rate of total soil moisture are also found to be soil texture specific.Results obtained by both IRE and FEM methods are in good agreement,indicating that the simple IRE method is reliable and can be used for modeling soil water dynamics.