青藏高原冻土退化对地表水文过程的影响和贡献

Persistent increase in air temperature causes the dramatically degradation of permafrost on the Qinghai-Tibet Plateau (QTP), which changes the recharge processes of permafrost meltwater to the surface water, and significantly alters the surface hydrological processes in permafrost regions on QTP. Changes in surface hydrological processes will extensively influence the dynamic changes and allocation patterns of water resources on QTP. However, the resultant hydrological effects of permafrost (ice) thaw on surface hydrological processes and quantitative estimation studies are not well documented currently. Considering the regional differentiations in permafrost distribution and ground ice contents, the impacts of permafrost degradation on the surface hydrology were not consistent in different areas of QTP. This program will select three most representative regions with different frozen soil (permafrost) and ground ice conditions, aims at studies on the impact of permafrost degradation on the surface hydrological processes on QTP. The stable and radioactive isotopic methods were employed combining with in-situ permafrost hydrological observation ways to reveal the seasonal variations of active layer hydrology, and subsequent elucidation of the recharge processes of suprapermafrost water and permafrost (ground ice) meltwater to surface water components. Additionally, the program also will quantitatively estimate the recharge contribution of permafrost (ground ice) meltwater to surface water. Finally, the parametric model is built to simulate and predict the impact of permafrost degradation on surface hydrology under different air temperature rise patterns on QTP in the coming decades. The program results will provide data support and theoretical basis in intensive study on the permafrost hydrology and water resources assessment of QTP, also offer important references to water system dynamic evolution and cryosphere change research in permafrost regions.

青藏高原持续升温导致冻土退化加剧，改变了冻土融水对地表水体的补给过程，使得冻土区的地表水文过程发生显著变化，对青藏高原水资源的动态变化产生重要影响。由于青藏高原冻土和地下冰分布的区域差异，冻土退化对地表水文过程的影响不尽相同。目前对不同冻土类型和含冰量条件下冻土退化产生的水文变化及其定量研究还处于初步探索阶段。因此，本项目拟选择青藏高原三个有典型代表性的研究区，基于稳定和放射性同位素技术，结合野外水文观测，开展青藏高原不同冻土和含冰量区域冻土退化对地表水文过程的影响研究。通过揭示活动层水文过程的变化规律，阐明冻结层上水和冻土融水对地表水体的补给过程，定量估算冻土融水对地表水体的补给量，模拟预测未来不同升温模式下青藏高原冻土退化对地表水文过程的影响和贡献。为深入研究青藏高原冻土水文过程和水资源评估提供数据支持和理论依据，为冻土区水循环系统动态演化和冰冻圈变化研究提供重要的借鉴和参考。

青藏高原持续升温导致冻土退化加剧，改变了冻土融水对地表水体的补给过程，使得冻土区的地表水文过程发生显著变化。本项目选择青藏高原两个不同冻土和地下冰分布类型的典型区域开展水文过程研究工作。通过野外径流观测、长序列周期性采样工作以及同位素示踪技术，分析了河水、热融湖塘、冻结层上水以及地下冰同位素时空变化规律，揭示了冻土和地下冰对径流量、湖塘水量平衡的影响，最终定量估算了地下冰融水对河流和湖塘的水文贡献量。研究结果显示，降水是冻结层上水的主控因素，但是在融化季，冻土和地下冰融水的贡献不可忽视。浅层地下冰主要受到夏季降雨、冻结层上水和冬季降雪的补给。径流观测结果显示，9-10月径流量出现峰值，主要受到降水和冻土（地下冰）融水的补给。基于径流分割模型计算显示，降水对河水的贡献占52-53%，浅层地下冰融水贡献率为13.2-16.7%。另外，地下冰融水的贡献量呈现出显著的季节差异，8月和9月，其贡献斜率高达22.55-31.9%，体现了冻土退化对地表径流过程的显著影响。另外，在冻土退化背景下，受蒸发、降水和地下冰融水的协同影响，热融湖塘水量平衡发生显著改变，且呈现出明显的时空差异。8-10月，夏秋季节降水和地下冰融水是高原热融湖塘水量平衡的决定性因素。最后基于同位素技术构建了冻土退化背景下青藏高原冻土水文概念模型，揭示了区域降水、地下冰以及地下水之间的水力联系。本项目研究结果首次将地下冰作为冻土水文循环的重要单元，定量估算了地下冰融水的水文贡献，为青藏高原冻土区水循环以及冻土生态环境研究提供重要的基础数据和技术借鉴。