祁连山高山寒漠带冻土导热系数观测实验研究

Alpine cold desert accounts for about 20%~30% of mountain areas in Tibet Plateau and Tianshan regions. It is an important hydrological functional area, which is largely affected by the distribution of frozen soil, freezing-thawing process and its hydrothermal condition. Accurate thermal conductivity is the key to analyse the permafrost change and freezing-thawing process, and to promote the related research on hydrology, climate model and land surface process model in alpine cold desert. However, due to the limitations of high altitude, harsh environment, coarse particles and difficult observation and sampling, observational and experimental research on the thermal conductivity of frozen soil in the alpine cold desert is extremely scarce, and typical estimation models mostly generalize or even neglect the influence of coarse grains. For this reason, this project is going to systematically carry out the observational and experimental research on the thermal conductivity of frozen soil in the alpine desert of Qilian Mountains. Based on long-term field investigation and laboratory experiments, the parameterization scheme of the influence of coarse particles will be improved, and an appropriate estimation model of thermal conductivity will be constructed. This study will provide key parameters for the study of frozen soil hydrology, ecological hydrology, climate model and land surface processes in the Qilian Mountains National Park.

高山寒漠带在青藏高原、天山地区的面积比例约为20%~30%，为寒区流域的主产流区，其水文过程在很大程度上受冻土分布、冻融过程及其水热状况影响。较为准确的导热系数，是把握高山寒漠带冻土变化及冻融过程，进而推进冻土水文、气候模式、陆面过程模式等相关研究的关键。然而，受海拔高、自然条件恶劣、颗粒较粗、观测取样困难等条件限制，高山寒漠带冻土导热系数的观测实验研究极为匮乏，已有经典冻土导热系数模型对该区土/岩参数化方案考虑不足。为此，本项目拟以祁连山高山寒漠带发育典型区为研究对象，野外调查和室内实验相结合，系统开展祁连山高山寒漠带冻土导热系数的观测实验研究，通过改进模型中粗质颗粒对土壤基质导热系数影响的参数化方案，构建适用于高山寒漠带不同类型土/岩的冻土导热系数估算模型，为祁连山国家公园冻土水文、生态水文、气候模式及陆面过程等相关研究提供关键参数。

作为寒区流域的主产流区，高山寒漠带的水文过程在很大程度上受冻土分布、冻融过程及其水热状况影响。作为控制冻土变化及冻融过程的关键参数，高山寒漠带冻土导热系数的相关研究有助于推进该区域冻土水文、气候模式、陆面过程模式等的研究。然而，受海拔高、自然条件恶劣、颗粒较粗、观测取样困难等条件限制，高山寒漠带冻土导热系数的观测实验研究极为匮乏。在本项目支持下，项目组在祁连山高山寒漠带发育典型区域进行了广泛的调查取样工作，通过室内颗分、控温控水试验等，试图揭示高山寒漠带冻土导热系数的主要影响机制，主要结论如下：1）祁连山区高山寒漠带土壤质地以粗颗粒为主。砾石（粒径>2mm）的平均体积比例约为63.3%，平均质量比例超过75%。粒径为20–40mm的砾石的体积和质量比例最高，其次是10–20mm，粒径>60mm的砾石比例最低。土壤孔隙度范围为9.5%–23.8%，平均值约为16.7%；2）冻土导热系数与粒径、含水率、温度密切相关。干燥状态下，导热系数随温度的升高（−20°C~25°C）呈逐渐增加趋势。土壤的砾石体积和质量比例越高，土壤孔隙度越小，则导热系数越高。饱和状态下，样品在冻结条件下的导热系数明显高于未冻结条件下。这可能是由于冻结状态下冰的导热系数（2.29W/mK）远高于融化状态下水的导热系数（5℃时为0.57W/mK）。在冻融过渡期间，频繁的冰-水相变会引起观测数据较大的波动。基于以上发现，项目组初步构建了基于粒径、含水率、温度等变量的高山寒漠带冻土导热系数的估算模型。除此之外，项目组开展了相关的延伸研究，如在区域乃至全国尺度上，开展了地温、地气差时空分布以及土壤冻融过程的研究工作。本项目累计资助（第一标注）发表SCIE论文5篇，完成了预设目标。