积雪边界条件下冻融土壤水热耦合迁移模型及数值模拟研究——以松嫩平原黑土为例

Snow cover is the most common and important boundary condition of freezing and thawing soils in the black soil region of Songnen Plain. The complexities of the physical process of moisture and heat transfer within snow and the dynamic moisture and heat connections between snow and soil cause high uncertainty and great error to quantitative descriptions of moisture and heat transfer in freezing and thawing soils covered by snow. To formulate moisture and heat connections between snow and soil quantitatively and simulate and predict moisture and heat transfer in freezing and thawing soil covered by snow more precisely, we plan to carry out experimental and theoretical studies to identify key factors influencing moisture and heat fluxes output from snow cover bottom by numerical simulation experiments of complicated and elaborate snow mode, to reveal moisture and heat transfer regularities of topsoil under different snow conditions and present response functions between snow and topsoil moisture and temperature, to optimally estimate soil moisture and heat transfer parameters and model and simulate coupled moisture and heat transfer in freezing and thawing soil covered by snow. The research results have important theoretical values and practical significances to reveal mapping relations between snow and soil surface moisture and heat, to complete theoretical system of moisture and heat transfer in freezing and thawing soil, to realize quantitative regulation of soil moisture and heat in freezing and thawing period, and to improve use efficiency of moisture and heat resources of the black soils in Songnen Plain.

积雪覆盖是松嫩平原黑土区最普遍和最重要的冻融土壤边界条件形式，积雪内部水热迁移物理过程及积雪与土壤水热动态联系的复杂性，给积雪边界条件下冻融土壤水热迁移的定量化描述带来了很高的不确定性和较大的数值模拟误差。为定量表征积雪与土壤的水热联系，更准确地模拟和预测积雪边界条件下冻融土壤水分运动和热流传导过程，本项目将在试验研究和理论分析的基础上，通过复杂精细积雪水热迁移模式的数值模拟试验，识别影响积雪底面水热通量输出的关键因子；揭示不同积雪条件下土壤表层水热状况变化规律，建立积雪-土壤表层含水率、温度响应函数模型；优化估计土壤水热迁移特征参数，构建积雪边界条件下冻融土壤水热耦合迁移数学模型并进行数值模拟分析与验证。研究成果对于揭示积雪与土壤表层水热映射关系，完善冻融土壤水热迁移理论体系，实现冻融期土壤水热定量调控，提高松嫩平原黑土水热资源利用效率具有重要的理论价值与现实意义。

为解决积雪边界条件下冻融土壤水热迁移研究中的诸多问题，本项目以松嫩平原黑土为例，采用试验与理论分析相结合的研究方法，开展积雪边界条件下冻融土壤水热耦合迁移模型及数值模拟研究。通过积雪边界条件下土壤水热状况分析，揭示了积雪厚度与密度对冻融过程、土壤温度及水分的影响差异性显著；通过多元回归分析，建立了积雪边界条件下土壤温度的响应函数，土壤表层20cm深度的多元回归精度较高；采用萤火虫算法解决了van Genuchten模型参数优化的非线性拟合问题，准确估计了土壤水动力学参数；建立了积雪边界条件下冻融土壤水热耦合迁移数学模型，利用数学模型对不同积雪边界条件下土壤含水率和温度变化情况进行了数值模拟，模拟值与实测值比较验证了数学模型的模拟精度；运用风险分析方法，估计了由于积雪边界条件的不确定性带来的农田春季旱涝风险，研究区域农田春季易涝旱的风险基本持平，极易干旱的风险大于极易涝害的风险；通过数值模拟试验，确定了研究区域农田春季抗涝阈值为融化前实测积雪厚度30~50cm，抗旱阈值为10~20cm。研究成果可为寒区土壤水热调控与墒情管理提供理论基础，为冻融期土壤水热迁移研究提供思路与参考。