季节性冻融期土壤蒸发规律的试验及模拟研究

Freeze-thaw soil evaporation in winter and spring has attracted much attention because it directly affects the efficient utilization of soil water and the sustainable development of agriculture in arid and semiarid climate zones. However, the effective reduction of soil evaporation during freezing and thawing period is severely restricted by two factors: 1) the driving mechanism of coupled water, heat and salt migration and the soil evaporation rules under different ground control measures; and 2) the lack of feasible soil evaporation prediction method. Based on series of soil evaporation tests in field, physical simulation experiments of indoor and outdoor soil evaporation, combining with numerical simulation, this study will focus on the following aspects: Firstly, revealing the influence mechanism of soil freezing and thrawing on soil evaporation; Secondly, exploring the mechanism of soil evaporation blocked by existence of the heterogeneous layers near the surface; Thirdly, inquiring into the soil evaporation rules of bared stubble and deep ploughing land covering with maize stalks, plastic film and silt under winter-spring irrigation conditions; and analyzing the effect of soil texture, soil structure, frozen characteristics and groundwater depth on soil evaporations; Fourthly, building the experiential models for calculating soil evaporation, which take atmosphere evaporation capacity, soil freezing-thawing chracteristics, soil temperature or cumulative negative temperature and liquid water content as the crucial factors; and Finally, establishing one -dimension models of coupled water, heat and salt migration including three-phase transformation of soil water to realize the dynamic forecasting of soil evaporation during winter and spring seasons. This study will enrich the research field of hydrogeology in vadose zone and land surface process in permafrost region, and finally open a new way for reducing soil evaporation and improve water-use efficiency both in theory and in practice.

冬春季节冻融土壤蒸发因直接关系到干旱、半干旱气候区土壤水资源高效利用、农业可持续发展而备受关注，冻融期不同地面调控措施下水热盐耦合迁移驱动机制及蒸发规律不清、可行的蒸发量预报方法欠缺，是目前蒸发有效抑制的瓶颈。本研究采用系列田间土壤蒸发试验、室内外蒸发物理模拟实验与数值模拟相结合的方法，揭示土壤冻结、融化作用对土壤蒸发的影响机理；探索土壤剖面地表附近非均质层对土壤蒸发的阻滞机制；研究冻融期裸茬地和深耕地在不同地表调控措施（地表秸秆覆盖、粉砂层覆盖、地膜覆盖、冬春灌溉）下土壤蒸发规律；分析土壤质地、结构、冻结特征、地下水位埋深对蒸发的影响。构建以大气蒸发能力、土壤冻结特征、地温或累积负温和液态水含量为主要因子的蒸发量预报经验模型；建立包含水分三态相变的垂向一维水热盐耦合迁移数值模拟模型，实现冬春季节土壤蒸发的动态预报。本研究将从理论和实践上为抑制土壤蒸发、提高水资源利用率开辟新途径。

探索季节性冻融期的土壤蒸发规律，寻求科学、合理可行的保墒措施，已成为干旱、半干旱气候区水资源高效利用、农业生产可持续发展的关键问题之一。以山西省水文水资源勘测局太谷均衡实验站为试验基地，本项目采用系列田间土壤蒸发试验、室内外蒸发物理模拟实验与数值模拟相结合的方法，主要完成了不同地表调控下的田间土壤蒸发试验、不同冬春灌溉条件下田间土壤蒸发试验、田间非均质土壤蒸发试验、室内物理模拟蒸发试验、覆盖层—冻土—非冻土系统水、热耦合迁移数学模型的建立、验证等工作，探讨了冻融期土壤蒸发规律、影响因素及蒸发机理。选取影响土壤蒸发的气象因子和土壤水热特征因子共9个影响因素，采用主成分分析法分析了不同地表处理条件下影响冻融土壤蒸发的主要因素；基于数据驱动的人工智能算法研究了冻融土壤蒸发预报模型。主要结果：土壤深耕对冻融期土壤蒸发具有抑制效果，冻前灌水对稳定冻结阶段土壤蒸发影响小。冻融期地表不同粒径砂层覆盖对土壤蒸发的影响显著，随着覆砂粒径的增加，对土壤蒸发的抑制效果越明显。覆砂厚度1cm、2cm、3cm和4cm的土壤冻融期累积蒸发量分别为24.5mm、20.1mm、17.6mm和16.7mm，较裸地分别减少2.4%、20%、30.1%和33.7%。冻融期不同地表处理条件下的土壤累积蒸发量随时间的变化较好地符合幂函数关系。研究成果可为解决干旱半干旱地区土壤储水保墒、抑制土壤水无效耗散提供依据，同时可为干旱、半干旱气候区水资源评价和节水型农业的发展提供理论和实践应用的指导。