高寒山区土壤水“二元性”和径流水分来源解析的示踪研究

The Two Water Worlds (TWW) hypothesis suggests that soil water can be separated into two parts: mobile water, which eventually enters the stream, and bound water used by plants, and the two pools will not mix each other. Recent works showed that the TWW phenomenon is widespread across different climate and biomes. It challenged the traditional concept of translatory flow, current mechanism of soil water movement and theories on water source apportioning. Deeper understanding of the TWW theory is a crucial issue for the study of catchment hydrological process. However, current researches are still mainly focus on how to explain the phenomena, and the formation mechanism is not yet well investigated. Streamflow in cold and high mountainous regions originates from multi-sources, including rainfall, snow melting, ice melting, etc. Accurate water source apportioning can reduce the uncertainty of runoff forecasting and contribute to more knowledge of runoff variation. This project takes a sub-catchment of Yarlung Zangbo-Brahmaputra River basin as a case study to conduct comprehensive observations in different water pools and establish soil water movement model. It aims to: 1) reveal the mechanism of soil water movement in the high mountainous regions; 2) develop TWW hypothesis and innovate the theory of water source apportioning; 3) reveal the flow path of water in the cold and high mountainous regions. This project is an advancement on the frontier of hydrological studies, and is an interdisciplinary research on hydrology, pedology and ecology. It is promising to develop novel theories and methods on water source apportioning and contributes to the development on hydrological model and runoff forecasting.

土壤水“二元性”（TWW）即植物蒸腾吸收与最终流入河道的土壤水存储状态不同且不发生混合，该理论在不同气候和植被带的证明颠覆了传统的平移流理论，对当前的土壤水运动机理和水源解析理论构成巨大的挑战，是流域水文过程研究的一个重要方向，但当前还处于对TWW的概念性解释阶段，对其形成机理尚缺乏深入的认识。对于由降雨、冰雪融水等多种水源组成的高寒山区河流，径流水分解析有助于减少径流预测的不确定性，加深对径流变化的认识。本申请项目以雅鲁藏布江典型支流流域为对象，通过开展综合观测，揭示高寒山区土壤水运动机理，发展“二元土壤水”理论，建立高寒山区土壤水运动模型，创新水源解析理论，揭示高寒山区的具体水流路径。本申请在水文学国际前沿问题上进行探讨，属于水文学、土壤学和生态学的交叉研究，有望创新土壤水运动和径流水源解析理论和方法，促进水文模型和预报的发展，具有重要的理论和应用价值。

高寒山区是我国诸多大河的发源地，河道径流水源组成复杂。准确解析河道径流组分有助于揭示径流演变规律、实现径流过程的精准预报。本项目通过开展同位素水文对比观测，揭示了西藏然乌湖流域和北京西台子流域土壤水的“二元性”特征；集成研发了三维水文水动力模型HHMM（Hydrology Hydraulic Module Modeling），为高寒山区流域的水流路径模拟提供了工具支撑；基于耦合同位素示踪过程的分布式水文模型THREW-T（THREW, tracer-aided version），解析了雅鲁藏布江流域径流组成和典型冰川小流域的径流滞留时间。取得的具体研究成果如下：.（1）分析了土壤水的“二元性”特征：总结了土壤水“二元性”在全球不同气候区的表现特征，详细阐述了造成不同水库氢氧稳定同位素值差异的主要原因；发现西台子流域和然乌湖流域均存在土壤水“二元性”现象，其表现特征受树木种类、树木年龄、土壤属性等因素共同影响。.（2）创新了水文过程模拟方法：集成研发的HHMM模型耦合了一维土壤入渗模块、二维地表水运动模块、三维土壤水-热-盐-冰模块，实现了水文、能量和溶质循环过程的耦合模拟；基于HHMM模型在北京西台子实验山坡和西藏然乌小流域开展了水流路径模拟。.（3）解析了高寒流域的径流组成和滞留时间：基于THREW-T从输入水源和产流路径对雅鲁藏布江的径流组成进行了解析；基于THREW-T的示踪模块，建立了质量混合和流量追踪两种滞留时间的估算方法，并应用于冰川区小流域卡鲁雄曲，对流域径流运移时间和储水的滞留时间进行了估算，估算结果与已有较为成熟的正弦方法的结果较为吻合。