基于多圈层水文模型的羌塘高原内流区湖泊群快速扩张机理研究

Due to lack of in situ observations in the Tibetan Plateau (TP) and insufficient descriptions about the physical process of the multi-sphere (atmosphere, cryosphere and hydrosphere) interaction in the hydrological model, the driving factors of most lakes expansion or shrinkage have not yet been fully understood at present in the TP. This study selected the lake groups in the Inner Basin of Qiangtang Plateau as an example and studied the interaction mechanism between lakes and cryosphere hydrological process. The main works include: (1) The multi-sphere hydrological model (WEB-DHM) in the TP is treated as the foundation, and the lake sub-module based on the lake hydrodynamic process is coupled into the WEB-DHM. The description of glacier melt process in the WEB-DHM is also improved. The dynamic description among the climate in the basin, cryosphere hydrological process and lake response will be realized. (2) The improved model is validated using field observations from typical lake basins and remote sensing data. Long-term hydrological processes in the “lake-basin” system (lake area is greater than 100km2) are simulated based on the validated model. (3) The effects and contributions of each component, including precipitation, surface runoff, snow and glacier melt, permafrost release and evaporation on the expansion of lake groups will be revealed from the simulated results. This study will enhance the understanding of the changing mechanism of lakes in the TP under the background of climate change.

限于青藏高原实地观测资料相对缺乏以及水文模型对多圈层(大气圈、冰冻圈和水圈等)相互作用的物理过程描述不足，目前大多数高原湖泊扩张或萎缩的驱动因子尚未得到充分认识。本研究以羌塘高原内流区湖泊群为研究对象，开展湖泊与冰冻圈水文过程的相互作用机理研究。主要包括：(1)在现有青藏高原多圈层水文模型(WEB-DHM)的基础上，将基于湖泊水动力过程的湖泊子模块耦合到WEB-DHM中并改进模型对冰川消融过程的描述，实现对流域气候—冰冻圈水文过程—湖泊响应的动态描述；(2)根据典型湖泊流域实地观测和遥感数据对改进后的模型进行验证，选取内流区面积较大的湖泊(100km2以上)，基于验证后的模型开展“湖泊-流域”系统水文过程的长期模拟；(3)基于模拟结果，揭示降水、地表径流、冰雪融水、冻土水分释放以及蒸发各分量对湖泊扩张的影响和贡献。在气候变化背景下，本研究将加深对青藏高原湖泊变化机理的认识。

湖泊是青藏高原的典型地表类型，是影响水循环的关键因子，也是地球表层系统冰冻圈、大气圈、水圈、生物圈（多圈层）连接的纽带。青藏高原的湖泊60%以上集中在羌塘高原，但限于实地观测资料相对缺乏，羌塘高原湖泊流域的水文过程和大多数湖泊演变的关键过程及驱动机制尚未得到充分认识。同时由于水文模型对多圈层相互作用的物理过程描述不足，目前对高原“湖泊-流域”的定量模拟仍然缺乏。. 本研究以羌塘高原内流区湖泊群为研究对象，在维护并完善典型湖泊流域观测体系的基础上，结合观测和多源遥感数据构建了内流区的基础数据库。发展了耦合3层积雪与土壤冻融物理模块的分布式冰冻圈水文模型（WEB-DHM-SF），并改进了模型中多年冻土物理过程和冰川消融过程的参数化方案，为开展“湖泊-流域”系统的水文模拟提供工具及计算平台。对参数化方案的验证表明，耦合模型能较好的捕获到冰冻圈物理过程的内在变化，并能很好的改进流域水文过程的模拟效果，但也还存在部分需要优化和改善的内容（如冰川消融方案在流域尺度上的应用）。对耦合模型在内流区开展了多变量多过程的验证，基于验证后的模型定量揭示了1979-2016年十个大型湖泊水储量变化（LWSC）的驱动机制。表明，降雨径流、湖面降雨、冰雪融水、湖面蒸发和土壤冻融对LWSC的贡献分别为60.2%—76.4%、13%—29.7%、20.5%—45.4%、‒38.4%—‒15.7%和2.1%—6.7%。其中降雨仍是主导因素，贡献超过80%。基于改进的方案计算了70个湖泊（面积大于100 km2）湖面蒸发及流域气象要素的长期变化趋势，陆续开展其他湖泊流域的模拟。发展并在典型湖泊验证了湖泊水动力模块，可用于评价湖泊对流域冰冻圈水文过程的响应，并将在优化模块热力参数后应用到更多的湖泊。本研究将加深对羌塘高原湖泊变化机理的认识，为深入理解“湖泊-流域”多圈层交互作用提供参考，为科学应对湖泊扩张提供依据。