蒸发条件下土壤水分响应模拟

Modeling soil moisture responses under evaporative conditions

基于有限元(FEM)和改进的积分型Richards方程解法(IRE方法)对蒸发条件下5种土体土壤水分响应进行了研究。数值实验结果表明:在土壤表面潜在蒸发量0.50 cm/d的情况下,5种土体土壤含水率变化曲线均呈现单拐点两阶段的特点,拐点出现在地表下20cm左右,拐点上部区域曲线曲率大于下部区域,两阶段的划分以15d左右为界,前阶段比后阶段的土壤水分变化快;蒸发模拟结果很好的证明了蒸发三阶段理论。总蒸发量和下边界排水量与土壤结构密切相关,而总水量变化量和变化率与土壤质地有关。IRE方法与FEM模拟结果基本一致,解法相对简单,模拟结果可靠性高。

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.