青藏高原多年冻土区活动层冻融过程区域差异及其影响因素的分析研究

The active layer is that portion of the soil above permafrost that thaws and freezes seasonally. The research on the active layer thawing and freezing processes was considered a key to revealing the heat and moisture exchanges between permafrost and atmosphere. The freezing and thawing processes of active layer are influenced by many factors, including local climate, physical and thermal properties of the surface cover and substrate, vegetation, soil moisture and so on. Under the influence of these physical factors, the freezing and thawing processes have great variation in spatial scale. So an analytical investigation of the freezing and thawing processes under the different climate and land surface condition is very important for the environment change research in permafrost area.The freezing and thawing processes have great space variation on Qinghai-Tibetan Plateau permafrost regions, which caused by its large area and complex mountain topography. At present, there are no detailed, systematic research on the freezing and thawing processes. In this project, three typical climate regions (Xidatan, Wudaoliang and Tanggula) were chosen to systematically study the spatial variation of active layer freezing and thawing processes at two spatial scales, different climate regional scale and the same climate regional scale. At the same climate regional scale, the land surface conditions of vegetation, soil water content and soil property will be selected to study their influence on the freezing and thawing processes, and a relationship model between these factor variables and active layer thawing/freezing depth was expected to be constructed. At the different climate regional scale, the influence of climate conditions on the freezing and thawing processes will be studied. Finally, a relationship model between all these physical factor variables and active layer thawing/freezing depth was expected to be constructed.

活动层是指位于多年冻土层之上、地表下一定深度内冬季被冻结、夏季被融化的岩土层,对活动层冻融过程的研究被认为是揭示多年冻土区陆-气水热交换过程的关键。活动层的冻融过程受气候、植被、土壤水分和岩土性质的影响表现出明显的空间差异，所以对活动层冻融过程的区域差异及其影响因素的研究在多年冻土区环境变化研究中具有重要意义。在青藏高原多年冻土区，其复杂的地貌环境和大面积的多年冻土分布，活动层的冻融过程表现出巨大的空间差异，而目前还没有这方面的系统研究。本项目决定在青藏高原多年冻土区选取三个典型代表区域（西大滩、五道梁、唐古拉），分两个空间尺度研究气候因素与局地因素对活动层冻融过程的影响。在相同气候条件下的空间尺度内，主要研究植被、土壤水分和岩土性质对活动层冻融过程的影响，在不同气候区域空间尺度主要研究气候条件对活动层冻融过程的影响，最后建立各因素参量与活动层冻结/融化深度关系模型。

活动层是指位于多年冻土层之上、地表下一定深度内冬季被冻结、夏季被融化的岩土层,对活动层冻融过程的研究被认为是揭示多年冻土区陆-气水热交换过程的关键。活动层的冻融过程受气候、植被、土壤水分和岩土性质的影响表现出明显的空间差异，所以对活动层冻融过程的区域差异及其影响因素的研究在多年冻土区环境变化研究中具有重要意义。本项目在青藏高原多年冻土区选取三个典型代表区域（西大滩、五道梁、唐古拉），分两个空间尺度研究了气候因素与局地因素对活动层冻融过程的影响，最终建立了各因素参量与活动层冻结/融化深度关系的映射斯蒂芬模型。.研究结果表明，活动层的冻融深度主要受地表温度积温值、土壤水分、土壤有机质含量及土壤容重四个因素影响。由于土壤有机质和土壤容重主要影响土壤的热导率，因此影响活动层冻融过程的因子最终可以定量化的表述为地表积温值、土壤含水（冰）量和土壤热导率三个因子。本项目最后构建了一个斯蒂芬映射算法模型，解决了斯蒂芬方程在非均质土壤条件下模拟活动层冻融过程的问题。原始的斯蒂芬方程只能计算均质土壤条件下土壤的冻融过程计算，即假定土壤的含水（冰）量和热导率为定值。本项目通过研究发现，在利用斯蒂芬方程计算活动层冻融过程中，可以把非均质土壤层分割为多层土壤（分层数足够满足土壤水分、热导率的刻画精度），利用修改的土壤水分、热导率参数和分层深度数据反算地表积温量，再通过映射关系建立实测地表积温量和计算地表积温量之间的关系，从而可以有效模拟非均质土壤条件下活动层的冻融过程。