拉萨河典型流域表层结构与径流响应关系的解析及模拟研究

Lhasa River Basin as well as the whole Tibetan Plateau region is among one of the most complex continental ecosystem on the Earth. However, the shortage of hydrologic observations has limited the development and utilization of hydrology and water resources in this region. Nevertheless, hydrologic observations themselves have to face many challenges, e.g., extrapolating observations of watershed behavior. Hence, new schemes and ideas towards systematically understanding of hydrologic regimes on the Plateau basins should be adopted. .In this study, Duodigou Catchment in the Lhasa River basin is selected as the experimental station and we try to reveal the mechanism of how freezing thawing of snow (soils) and rainfall impact runoff responses through different structures. The nested observations, which include several precipitation and runoff stations and one hillslope trough observation for hydrologic connectivity during freezing thawing season, will be set up in Duodigou Catchment. The distribution of catchment critical zone structures will be analyzed through field samples and laboratory tests of physicochemical properties of soils and rocks. Then the statistically- and physically-based models are developed for the predictions of structural attributes (e.g., soil depth) in the catchment critical zone. The hillslope storage dynamics model is modified for prediction of storage-discharge processes under freezing thawing conditions, and analytical solutions for the model’s basic equations are further derived to analysis the relationship between storage, hydrologic connectivity and catchment structures. The last but not the least, this study can provide an observation platform and scientific data for the whole project. It will provide helps for understanding hydrologic regimes in the Tibetan Plateau basins and will promote hydrologic predictions in the region.

拉萨河流域及其所在的青藏高原区是世界上最为复杂的陆地生态系统之一。然而，本区的水文观测严重不足，限制了该区工程水文及水资源开发利用工作的开展。此外，当前水文观测本身也面临诸多挑战，如观测结果的移用等。因此，针对高原区，需设计新的观测方案、理念以系统解析其水文响应的物理机制。本研究选取拉萨河夺底沟小流域为对象。通过野外勘测，发现流域表层结构的分布规律，发展高山深谷型流域结构特征空间分布定量描述与预测的方法。建立小流域嵌套式的水文强化观测网络，重点观测积雪（土）冻融作用下的水分蓄泄过程，分析不同结构特征子流域（山坡）的径流规律。构建考虑雪土冻融作用的蓄量动力模型，解析水分蓄量、水文连通性与流域结构的关系，并模拟高原小流域径流过程。此项目是基础的水文研究，它将帮助我们认识流域水文物理规律，提高该地区的水文预测能力，还将为重大计划后续项目提供典型区的实验平台和科学数据，是重要的先行工作之一。

拉萨河流域及其所在的青藏高原区是世界上最为复杂的陆地生态系统之一。然而，本区的水文观测严重不足，限制了该区工程水文及水资源开发利用工作的开展。此外，当前水文观测本身也面临诸多挑战，如观测结果的移用等。因此，针对高原区，需设计新的观测方案、理念以系统解析其水文响应的物理机制。本研究选取拉萨河夺底沟小流域为对象。通过野外勘测，揭示了拉萨河流域山坡地形、裸岩和土壤厚度等关键带表层结构的空间分布规律，发现高山区土壤厚度有随地形特征呈线性变化的趋势。随后，我们发展了基于地貌演化理论的高山区土壤厚度预测模型，给出了流域裸岩土壤的高精度分布图。为给土壤厚度预测模型提供精确的流向信息，我们还发明了新型单流向算法（iFAD8），与传统的D8方法相比，该算法可将水流路径的提取精度提高50%以上。随后，我们分析了拉萨流域降水和积雪的时空分布特征，揭示了气候变暖下羊八井小流域冰川融水与径流、地下水蓄量增量间的不平衡现象，发现流域径流增加主要由冰川融水贡献。随着温度的上升，冻土退化一方面增大了地下水储水空间，允许更多的融水渗入深层并缓慢释放为基流，另一方面又打通了深层渗漏的通道，造成了水量的不平衡现象。在关键带结构及径流响应变化规律认识的基础上，我们发展了基于关键带结构特征的水文模型参数估算方法，利用所推导的临界蓄量响应公式改进了概念性水文模型的产流理论。基于上述理论，构建了适用于高原寒区的分布式水文模型，实现了高寒高山区产流计算模型参数的免率定。此项研究是基础水文工作，可为重大研究计划积累大量第一手的数据，该项研究理论成果将推进西藏工程水文计算方法发展，可为西南河流源区同类流域提供可靠的水文预测理论和方法。