Knowledge Resource Center for Ecological Environment in Arid Area
| 青藏高原北麓河盆地多年冻土特征及其对气候变化的响应研究 | |
| 其他题名 | Features of permafrost in the Beilu'he Basin in the Interior of the Qinghai-Tibet Plateau, Southwestern China and their response to climate change |
| 尹国安 | |
| 出版年 | 2017 |
| 学位类型 | 博士 |
| 导师 | 牛富俊 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 全球正在经历前所未有的变暖过程，全球多年冻土的退化给冻土区的水文、生态、人类工程活动带了巨大的挑战。青藏高原多年冻土区重大工程的建设和灾害评估对于高精度多年冻土分布图的需求也越来越强烈。研究青藏高原多年冻土与局地环境因素之间的关系，并且建立合理的冻土模型不但有利于理解青藏高原多年冻土与气候以及生态系统之间的相互关系，而且对青藏高原多年冻土区的重大工程的稳定性设计和灾害评价具有重要意义。目前青藏高原的观测站点多数沿着青藏铁路和公路，传统上对冻土区的模拟仅仅局限在大尺度上的统计经验模型上，并没有详细考虑局地因素的影响。北麓河盆地位于青藏高原腹地，平均海拔4628 m，具有青藏高原典型的气候特征、植被土壤特征以及多年冻土特征。同时，北麓河盆地已经是我国乃至国际重要的低纬度高山多年冻土研究基地，具有较为详细和连续的与多年冻土有关的观测资料。因此，本文以青藏高原北麓河盆地为研究区，利用多种研究方法，建立了精细化的观测场地，在取得大量宝贵冻土环境和冻土特征资料基础上，获得了如下主要结论。（1）利用遥感分类技术，提取了北麓河地区的高分辨率空间植被信息和土壤信息，据此获取编制了北麓河地区的植被和土壤分布类型图。地貌类型主要有10种，而其中有5中主要的地表植被类型，占据了整个盆地约90 %面积。本论文研究设置的观测网络覆盖了这5种植被类型：沼泽草甸、高山草甸、退化草甸、高山草原和沙漠化草原。因此，其研究结果基本上能够代表北麓河地区的多年冻土特征。（2）地质雷达和钻孔勘测结果显示研究区整体活动层土壤含水率较低，但地下冰的含量有很大的空间差异。地下冰的差异分布与地貌、土壤组成、水文条件密切相关。通过地统方法—反距离加权插值方法，获取了北麓河地区浅地表层平均含水/冰量的空间分布图。两年地温监测数据数据显示，北麓河地区多年冻土的地温较高，在-1.5~0 °C之间，这属于高温多年冻土区，对气候变化极为敏感。类似条件下，沼泽草甸与高山草甸区域的多年冻土地温要比退化草甸和沙漠化草原低。不同植被类型条件下多年冻土的发育与温度都有较为明显的差异。植被覆盖类型对多年冻土的热影响关系得到证实，即高山草甸对多年冻土具有保护作用，而在高山草原和沙漠化草原地区是多年冻土在过去10年发生不同程度退化现象。对不同地表条件下的地温日均值进行了聚类分析，阐明了地温变化与地表类型之间的关系，即沼泽草甸、高山草甸、退化草甸下冻土地温较低，而沙漠化草原下冻土温度较高，高山草原地区多年冻土退化或为融区。根据植被类型图获得了北麓河地区高分辨率大比例尺多年冻土空间分布图。（3）建立了关于北麓河盆地气候—生态—冻土的模型，并对模型进行了验证。模型具有较高的准确性和适用性。整体地温模拟结果与实测值之间相对误差为0.1~1.1 °C，活动层厚度误差为0.2 m以内。该模型考虑了不同地表因素的影响，并耦合了大气过程、地表过程与地下过程。敏感性分析表明，北麓河地区多年冻土地温以及活动层厚度对地表条件以及土壤水分较为敏感。（4）通过建立的模型对北麓河盆地多年冻土分布进行了高分辨率模拟，结果显示目前北麓河盆地面积约73.7 %之下分布多年冻土，活动层厚度平均为1.8 ~2.5 m。同时模拟表明过去30年北麓河多年冻土面积减少了约20 %，年平均地温增加了0.5 ~1.0 °C，活动层厚度增加了0.1~0.3 m。考虑到未来气候的不确定性变化，在0.015 °C/yr增温情景下，30年后冻土面积相对现状减少约3.3 %，主要表现为地温增加，沙漠化草原地区冻土退化；60年后冻土面积相对现状减少约17%。冻土退化区主要为沙漠化草原区，整体地温增加约0.5 °C。在0.065 °C/yr增温情景下，30年后多年冻土面积相对现状减少约29.6 %，多年冻土只存在于草甸区，；然而60年后多年冻土面积相对现状减少约46 %，年平均地温明显升高到-0.5~0 °C之间。（5）基于GIS平台对研究区热融灾害易发性进行了综合评估。研究区共分为4个热融灾害易发区：非易发区、低易发区、中易发区和高易发区。其中非易发区占区域总面积的20.4 %，低易发区占22.0 %, 中易发区和高易发区分别占19.6 % 和 31.7 %。含冰量、年平均地温以及工程活动扰动是影响热融灾害易发性的主要因素。 |
| 英文摘要 | Recent increases in near-surface air temperature have been pronounced in many regions of the world. This has led to permafrost degradation as ground temperatures and the active-layer thickness increase, which has impacted surface and subsurface hydrologic conditions, soil strength properties, ecosystems and infrastructure. Permafrost characteristic and its extent have unique regional features on the Qinghai-Tibet Plateau (QTP). A detailed and present-day knowledge of permafrost distribution and its relationships with local factors are essential as it may help the studies on the feedback mechanisms between the atmosphere and permafrost, the development of cold region engineering techniques, and the calibration and validation of spatially distributed permafrost models. Therefore, it is important to understand the conditions and active processes controlling the present state of permafrost on the QTP. However, most investigations are focused along sections of the the Qinghai-Tibet Engineering Corridor, or consist of sparse observations in large regions. The distribution and characteristics of mountain permafrost have only been assessed at a coarse scale due to the difficultly accessing such terrain on the QTP. The overall aim of this study was to establish a detailed permafrost observation network at local scale with multiple methods, and develop permafrost model for estimation of past, present and future permafrost conditions and distribution in the Beiluhe basin, which is located in the interior of the QTP. As a major outcome of this study, a physical permafrost model was developed and the first high resolution map of permafrost in Beiluhe basin was compiled.(1) The landform was classified into 10 types based on a high resolution satellite image. Most basin area (over 90%) was represented by 5 ecotypes: swamp meadow, undisturbed alpine meadow, degraded alpine meadow, alpine steppe, and desert alpine grassland. Our thermal monitoring network including a total number of 17 boreholes covered these five ecotypes.(2) Results based on drill cores and ground penetrating radar indicted that the near-surface soil is dry. The near-surface (0-5.0 m) mean volume ice-content extent was mapped by using Inverse Distance Weighting(IDW). The spatial differences of permafrost temperatures and active-layer thicknesses were investigated by comparing thermal conditions of the boreholes across different ecotopes. The mean annual ground temperature was from -1.5 to 0 °C，which indicated that permafrost is warm, and sensitive to climate change and surface disturbance. Active-layer thickness was ranged from 1.4 to 3.4 m. Permafrost was protected by alpine meadow but degrading at other ecotypes. Besides long-term climate condition, the thermal state of permafrost was influenced by the physical properties of the vegetation cover and subsurface material. As a proof of concept, we used the ground temperature data collected from the field boreholes to recode an ecotype and land cover map into a map of mean annual ground temperature ranges at 3.0 m depth based on analysis and clustering of observed thermal regimes. We demonstrated that classifying the landscape into general ecotypes is an effective way to scale up permafrost thermal data. The results indicated that permafrost was cold in swamp meadow, undisturbed alpine meadow and degradation alpine meadow. Alpine steppe is indicative of the absence of near-surface permafrost.(3) An one-dimensional numerical heat flow model was enhanced and developed, which allowed for local factors including vegetation and surface soil condition. This model was calibrated and validated using thermal data collected from field sites. This physical model resulted in a satisfactory accuracy with a relative error of 0.1~1.1 °C in simulating ground temperatures and that of 0.2 m insimulating active-layer thickness.(4) The impacts of climate warming on permafrost spatial distribution from 1985 to 2075 was assessed by using historical climate data and two scenarios of climate warming in the future. The ground thermal properties of surface vegetation and soil columns were up-scaled using the vegetation map and temperature data assimilation from the shallow boreholes across the Beiluhe basin. According to model results, 73.7 % of the basin is underlain by permafrost, and the mean active-layer thickness is 1.8 ~2.5 m across the basin. During the past 30 years, permafrost distribution decreased by 20 %, and the active-layer thickness increased by 0.1 ~ 0.3 m. With an increase of air temperature of 0.015 °C/yr in the future 60 years, permafrost distribution may decrease by about 17 % over the basin. The permafrost thermal states almost keep steady in alpine meadow. However, with an increase of an additional warming of 0.065 °C/yr until 2075, permafrost extent may decrease by about 46 %, and warm permafrost will only exist in alpine meadow.(5) Thermokarst hazard assessment was conducted in ArcGISTM. A thermokarst hazard susceptibility map was compiled for a representative region in the Beiluhe basin. The study region was divided into four classes based on the susceptibility: unlikely, low, moderate, and high. Areas classified as unlikely accounted for 20.4 % of the study region, while low susceptibility areas comprised 22.0 %. The moderate and high susceptibility zones comprised 19.6 and 31.7 %, respectively. |
| 中文关键词 | 多年冻土 ; 局地因素 ; 气候变化 ; 模型发展 ; 灾害评价 |
| 英文关键词 | Permafrost Local factors Climate change Model Hazard assessment |
| 语种 | 中文 |
| 国家 | 中国 |
| 来源学科分类 | 防灾减灾工程及防护工程 |
| 来源机构 | 中国科学院西北生态环境资源研究院 |
| 资源类型 | 学位论文 |
| 条目标识符 | http://119.78.100.177/qdio/handle/2XILL650/287960 |
| 推荐引用方式 GB/T 7714 | 尹国安. 青藏高原北麓河盆地多年冻土特征及其对气候变化的响应研究[D]. 中国科学院大学,2017. |
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