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冰川冻土 ›› 2021, Vol. 43 ›› Issue (2): 357-369.doi: 10.7522/j.issn.1000-0240.2021.0048

• 第二次青藏高原综合科学考察研究 • 上一篇    下一篇

下边界条件对多年冻土温度场变化数值模拟的影响

孙哲1,2(),赵林3(),胡国杰1,乔永平1,杜二计1,邹德富1,谢昌卫1   

  1. 1.中国科学院 西北生态环境资源研究院 冰冻圈科学国家重点实验室/藏北高原冰冻圈特殊环境与灾害国家野外科学观测研究站,甘肃 兰州 730000
    2.中国科学院大学,北京 100049
    3.南京信息工程大学 地理科学学院,江苏 南京 210044
  • 收稿日期:2021-01-05 修回日期:2021-03-03 出版日期:2021-04-30 发布日期:2021-05-18
  • 通讯作者: 赵林 E-mail:sunzhe@lzb.ac.cn;lzhao@nuist.edu.cn
  • 作者简介:孙哲,博士研究生,主要从事多年冻土模拟研究. E-mail: sunzhe@lzb.ac.cn
  • 基金资助:
    第二次青藏高原综合科学考察研究项目(2019QZKK0201);国家自然科学基金项目(41931180);中国科学院战略性先导科技专项(XDA2002010202)

Influence of lower boundary conditions on the numerical simulation of permafrost temperature field changes

Zhe SUN1,2(),Lin ZHAO3(),Guojie HU1,Yongping QIAO1,Erji DU1,Defu ZOU1,Changwei XIE1   

  1. 1.State Key Laboratory of Cryospheric Science / Cryosphere Research Station on the Qinghai-Tibet Plateau,Northwest Institute of Eco-Environment and Resources,Chinese Academy of Sciences,Lanzhou 730000,China
    2.University of Chinese Academy of Sciences,Beijing 100049,China
    3.School of Geographical Sciences,Nanjing University of Information Science and Technology,Nanjing 210044,China
  • Received:2021-01-05 Revised:2021-03-03 Online:2021-04-30 Published:2021-05-18
  • Contact: Lin ZHAO E-mail:sunzhe@lzb.ac.cn;lzhao@nuist.edu.cn

摘要:

在气候变暖背景下,北半球多年冻土呈现不同程度的退化趋势,冻土升温、活动层增厚、地下冰消融改变了区域工程地质条件、地形地貌,不仅对寒区环境和工程稳定性造成潜在的威胁,还影响着这些地区的气候、水文和生态过程。因此,准确评估和预估多年冻土热状况的变化具有重要科学和实践意义。现有用于模拟多年冻土热状况的各类模式重点考虑了近地表温度场变化对多年冻土的影响,主要集中于对气温和浅表层物理过程和参数化方案等改进和优化,而对于下边界条件设置对多年冻土热状况模拟的影响少有讨论。基于一维热传导冻土模型,以五道梁地区的多年冻土为研究对象,通过设置不同的下边界方案进行模拟实验,定量评估百年尺度气候变化下不同下边界条件对多年冻土温度场变化数值模拟的影响。结果表明:近地表层(<3 m)的温度场完全由年际气候变化决定,浅层(3~15 m)及中层(15~30 m)的多年冻土温度场受下边界条件的影响逐渐显著,深层(>30 m)的地温对百年尺度气候变化的响应不仅与气候变化的幅度有关,还与多年冻土相变热的多少有直接的关系。下边界条件不恰当的设置方式会对大尺度的气候变化下多年冻土消融程度的计算造成较大的影响,进而可能对深层地温乃至多年冻土区面积变化造成严重的误判。因此,开展百年尺度多年冻土温度场变化模拟时,应采用深层或多年冻土底板以下融土层的稳定地热流作为下边界条件。

关键词: 多年冻土, 地温场, 数值模拟, 下边界条件

Abstract:

Permafrost in the Northern Hemisphere has degraded in different degree under the climate warming. Permafrost degradation may have changed the regional engineering geological conditions, topography and geomorphology, which may have a great impact on regional climate, hydrological and ecological processes, and engineering infrastructures. It is essential to assess and predict the permafrost thermal state accurately by models. Most present models used to simulate permafrost thermal state focus on the effect of ground surface temperature on permafrost changes, so their research direction is the improvement and optimization of the parameterization for air temperature and the physical process in shallow soil layer. However, the influence of the temperature field in the lower part of soil layer, which is strongly affected by historical climate and geothermal energy, on the permafrost simulation is rarely discussed. A comprehensive observation station has been established in Wudaoliang region on the Qinghai-Tibet Plateau by the Cryosphere Research Station on the Qinghai-Tibet Plateau, Chinese Academy of Sciences. Long-term continuous monitoring data, such as meteorological factors, temperature and moisture content in the active layer, ground temperature of permafrost in different depths, were recorded in the comprehensive observation station since 2004. It provides a basic-data support for the establishment of permafrost model and the sensitivity analysis of each parameter for the simulation of permafrost temperature field. In this paper, we established an one-dimensional heat conduction permafrost model to assess the influence of different lower boundary conditions on the simulation of the permafrost temperature field in Wudaoliang. In our model, not only it takes the phase change, differences in thermophysical properties between frost and thaw soil, distribution of underground ice in consideration, but also it is flexible enough to set different boundary conditions. Nine different lower boundary condition schemes were designed to evaluate the influence of different lower boundary conditions on the numerical simulation of permafrost temperature field changes from bottom to top quantitatively. The simulated permafrost temperature fields in different schemes were validated by the measured ground temperature series from 2005 to 2015. Moreover, a reconstructed historical ground surface temperature series reaching back to 1960s and a future ground surface temperature series reaching to 2100 were used to force the model to evaluate the influence of climate change on a centennial scale on the simulation of permafrost temperature field from top to bottom quantitatively. The result shows that the temperature field in the near ground surface layer (<3 m) is completely determined by the interannual climate change, while the temperature field of the permafrost in shallow layer (3~15 m) and transitional layer (15~30 m) is affected by lower boundary conditions significantly. The response of temperature field in the deep layer (>30 m) to the climate change on a centennial scale is not only related to the magnitude of climate change, but also directly related to the phase change heat. Improper lower boundary condition may have a great impact on the calculation of the permafrost degradation degree under large-scale climate change, which may lead to serious misjudgement of the temperature field in the deep layer and permafrost area. Therefore, we give some suggestions about the setting of lower boundary condition according to permafrost simulation in different scenarios as follow: if simulation the thickness or of the active layer or the interannual temperature change in the active layer, the lower boundary condition could ignore geothermal energy (set to zero geothermal flux) and be set in transitional layer or below the depth of zero annual amplitude; if simulating the change of mean annual ground temperature (MAGT) of permafrost for ten years or more, the lower boundary condition should be set to constant geothermal flux and be set below the transitional layer; if simulating the permafrost changes on centennial scale, the lower boundary condition should be set to constant geothermal flux and be set in the deep layer or below the permafrost base. This study would provide theoretical information for the selection of the lower boundary conditions in permafrost simulation researches.

Key words: permafrost, ground temperature field, numerical simulation, lower boundary condition

中图分类号: 

  • P461+.4