东北多年冻土退化及环境效应研究现状与展望

东北多年冻土属中高纬度多年冻土,对气候变化非常敏感。数据模型模拟表明,21世纪东北多年冻土区气温会持续上升,显著的变暖将导致多年冻土退化。东北多年冻土呈现自南向北的区域性退化趋势,多年冻土区南部表现为南界的北移、融区的扩大和多年冻土的消失,而北部表现为多年冻土下限的上移、活动层厚度增大及地温升高等。多年冻土的退化会导致寒区生态环境的恶化,如兴安落叶松占绝对优势的天然林带锐减,林带北移,沼泽湿地萎缩等。随着多年冻土的迅速退缩和变薄,原多年冻土中蕴藏的碳将释放出来,对气候变化产生积极的正反馈,加速变暖,并影响全球碳循环。多年冻土退化导致其热状态失稳而造成寒区基础设施损坏,并且影响冻土微生物、碳循环、寒区生态和水文等,而它们是区域气候变化的重要因子,也将成为未来多年冻土研究的重点。而这些研究都需要长期的基础数据作支撑,因此需要进一步完善冻土参数监测网络,用模型厘清气候变化与多年冻土退化及其环境效应之间的关系。     

青藏高原多年冻土热融灾害发展预测

青藏高原多年冻土区是世界上中低纬度多年冻土面积最大的区域,气候变化引起青藏高原多年冻土区年平均地温上升、地下冰融化、多年冻土退化等问题。借助ARCGIS技术手段,通过地下冰计算模型和Stefan公式计算研究区不同气候变化情景模式下的地下冰体积含冰量和活动层厚度变化。结果表明:在未来几十年内多年冻土的分布范围将不会发生显著变化,多年冻土的主要退化形式为地下冰的消融、低温冻土向高温冻土转化;但本世纪末多年冻土将发生大范围的退化。这一过程将引起热融滑塌、热融沉陷等冻土热融灾害。将Nelson热融灾害风险性评价模式进行修正,对研究区灾害风险性进行评估区划。最大的危险区主要分布在西昆仑山南麓、青南山原中部、冈底斯山和念青唐古拉山南麓、喜马拉雅山南麓部分区域,在未来几十年内有加剧的趋势。     

Thermal hazards zonation and permafrost change over the Qinghai–Tibet Plateau

The Qinghai–Tibet Plateau is the largest permafrost region at low latitude in the world. Climate warming may lead to permafrost temperature rise, ground ice thawing and permafrost degradation, thus inducing thermal hazards. In this paper, the ARCGIS method is used to calculate the changes of ground ice content and active layer thickness under different climate scenarios on the Qinghai–Tibet Plateau, in the coming decades, thus providing the basis for hazards zonation. The method proposed by Nelson in 2002 was used for hazards zonation after revision, which was based on the changes of active layer thickness and ground ice content. The study shows that permafrost exhibits different degrees of degradation in the different climate scenarios. The thawing of ground ice and the change from low-temperature to high-temperature permafrost were the main permafrost degradation modes. This process, accompanied with thinning permafrost, increases the active layer thickness and the northward movement of the permafrost southern boundary. By 2099, the permafrost area decreases by 46.2, 16.01 and 8.5% under scenarios A2, A1B and B1, respectively. The greatest danger zones are located mainly to the south of the West Kunlun Mountains, the middle of the Qingnan Valley, the southern piedmont of the Gangdise and Nyainqentanglha Mountains and some regions in the southern piedmont of the Himalayas. The Qinghai–Tibet Plateau permafrost region is in the low-risk category. Climate warming exacerbates the development of thermal hazards. In 2099, the permafrost region is mainly in the middle-risk category, and only a small portion is in the low-risk category.     

天然气水合物研究现状与未来挑战

人类在21世纪后期面临着油气资源枯渴,寻求洁净高效的新能源成为科学界追求的目标。为此,近三十年来,世界各国相继投入了大量的资金和人力开展新能源研究。目前,人们在一种重要的新能源---气水合物的基础研究、地质调查、勘探开发等领域取得了较大的进展;但尚存在许多急待解决的重大理论问题,如天然气水合物形成与分解的动力学过程和地质条件,气水合物资源量计算办法,经济型天然气水合物开采、开发模式,气水合物对全球气候的影响等。天然气水合物作为化石燃料,具有巨大潜力;作为甲烷碳库,是海底地质灾害的诱因;作为温室气体,对全球气候变化有着重要的影响作用。天然气水合物研究未来面临挑战。     

中国的多年冻土──过去与现在

中国多年冻土区的总面积约占中国陆地面积的２２．４％，达２１５００００ｋｍ²。多年冻土的分布特征受气候条件在三度空间的变化所制约。自晚更新世以来，其分布情况已有相当的变化。在东次冰期最盛期，东北地区多年冻土南界曾推进到北纬４１—４２°，在全新世暖期，南界向北退缩，但晚更新世形成的冰楔和多年冻土至今仍存在于大兴安岭北部，全新世中期严寒期冻土有所扩展并形成冰楔。随着气候变化，中国西部高山和高原区高海拔冻土的分布下界已上移８００—１０００ｍ，但高山和高原的主要部分仍处于冰缘环境，有的地方在全新世还发育了共生型多年冻土。     

Active layer thickness variations on the Qinghai–Tibet Plateau under the scenarios of climate change

Climate change has greatly influenced the permafrost regions on the Qinghai–Tibet Plateau (QTP). Most general circulation models (GCMs) project that global warming will continue and the amplitude will amplify during the twenty-first century. Climate change has caused extensive degradation of permafrost, including thickening of the active layer, rising of ground temperature, melting of ground ice, expansion of taliks, and disappearance of sporadic permafrost. The changes in the active layer thickness (ALT) greatly impact the energy balance of the land surface, hydrological cycle, ecosystems and engineering infrastructures in the cold regions. ALT is affected by climatic, geographic and geological factors. A model based on Kudryavtsev’s formulas is used to study the potential changes of ALT in the permafrost regions on the QTP. Maps of ALT for the year 2049 and 2099 on the QTP are projected under GCM scenarios. Results indicate that ALT will increase with the rising air temperature. ALT may increase by 0.1–0.7 m for the year 2049 and 0.3–1.2 m for the year 2099. The average increment of ALT is 0.8 m with the largest increment of 1.2 m under the A1F1 scenario and 0.4 m with the largest increment of 0.6 m under the B1 scenario during the twenty-first century. ALT changes significantly in sporadic permafrost regions, while in the continuous permafrost regions of the inland plateau ALT change is relatively smaller. The largest increment of ALT occurs in the northeastern and southwestern plateaus under both scenarios because of higher ground temperatures and lower soil moisture content in these regions.     

青藏高原腹地各拉丹冬南北坡多年冻土考察初步结果

青藏高原唐古拉山南北两侧在地形地貌、地理和气候特征上存在显著差异,多年冻土的发育状况和特征也明显不同。受第二次青藏高原综合科学考察研究等项目资助,多年冻土对亚洲水塔的影响专题考察分队分别于2019年和2020年的10—11月对唐古拉山各拉丹冬南侧的色林错上游扎加藏布源区（简称“湖源区”）和北侧的长江上游沱沱河源区（简称“江源区”）进行了多年冻土野外考察。利用钻探、坑探、地球物理勘探等方法对多年冻土的分布边界、多年冻土剖面的地层、地下冰等特征进行了描述和取样,同步构建了多年冻土温度和活动层水热观测网络,为多年冻土对亚洲水塔影响的机理分析、数值模拟以及情景预估提供数据保障。对野外调查资料的初步分析认为,各拉丹冬南北两坡地层沉积类型和地下冰赋存状态存在明显差异,北坡多年冻土的热稳定性、地下冰含量、冰缘地貌类型多样性均高于南坡,但由于受到构造地热、河流融区等多种因素的影响,北坡的冻土分布形式更为复杂。江源区100 m钻孔剖面揭示了连续分布的、厚度大于50 m的地下冰;在该区域发现了多年生冻胀丘分布群,并利用钻探和地球物理勘探方法对该区域规模最大、结构最完整的冰核型冻胀丘进行了较为系统的勘察剖析。两次野外调查工作共采集钻孔岩心、表层土壤、冰水等各类样本近1.2万件,为后期区域冻土理化指标分析,冻土环境化学、古气候环境研究的开展奠定基础。     

黄河源区冻土特征及退化趋势

黄河源区位于青藏高原多年冻土区东北部边缘地带,是季节冻土、岛状多年冻土和在大片连续多年冻土并存地带.多年冻土层在垂向分布上有衔接状和不衔接状两大类.不衔接状又可分为浅埋藏(8m)、深埋藏(8m)和双层多年冻土等形式.从20世纪80年代以来,源区气温以0.02℃.a-1增温率持续上升,人类经济活动日益增强,导致冻土呈区域性退化.多年冻土下界普遍升高50～80m,最大季节冻深平均减少了0.12m,浅层地下水温度上升0.5～0.7℃.冻土退化总体趋势是由大片状分布逐渐变为岛状、斑状分布,多年冻土层变薄,冻土面积缩小,融区范围扩大.部分多年冻土岛完全消失变为季节冻土.     

Permafrost and climate in Europe: Monitoring and modelling thermal,geomorphological and geotechnical responses

We present a review of the changing state of European permafrost within a spatial zone that includes the continuous high latitude arctic permafrost of Svalbard and the discontinuous high altitude mountain permafrost of Iceland, Fennoscandia and the Alps. The paper focuses on methodological developments and data collection over the last decade or so, including research associated with the continent-scale network of instrumented permafrost boreholes established between 1998 and 2001 under the European Union PACE project. Data indicate recent warming trends, with greatest warming at higher latitudes. Equally important are the impacts of shorter-term extreme climatic events, most immediately reflected in changes in active layer thickness. A large number of complex variables, including altitude, topography, insolation and snow distribution, determine permafrost temperatures. The development of regionally calibrated empirical-statistical models, and physically based process-oriented models, is described, and it is shown that, though more complex and data dependent, process-oriented approaches are better suited to estimating transient effects of climate change in complex mountain topography. Mapping and characterisation of permafrost depth and distribution requires integrated multiple geophysical approaches and recent advances are discussed. We report on recent research into ground ice formation, including ice segregation within bedrock and vein ice formation within ice wedge systems. The potential impacts of climate change on rock weathering, permafrost creep, landslides, rock falls, debris flows and slow mass movements are also discussed. Recent engineering responses to the potentially damaging effects of climate warming are outlined, and risk assessment strategies to minimise geological hazards are described. We conclude that forecasting changes in hazard occurrence, magnitude and frequency is likely to depend on process-based modelling, demanding improved understanding of geomorphological process-response systems and their impacts on human activity.     

黄河源区高寒植被主要特征初探

位于青藏高原东北部多年冻土与季节冻土交错带的黄河源区高寒生态环境及其变化一直备受关注. 气候变暖、冻土退化条件下,为了解黄河源区不同冻土区植被状况,在源区布设了4个场地：查拉坪（CLP,源区南部连续低温多年冻土区）;扎陵湖南岸（ZLH,源区中南部岛状多年冻土区）;麻多乡（MDX,源区西部的不连续多年冻土区）;鄂陵湖北岸（ELH,源区中北部季节冻土区）. 结合植被调查和场地监测,分析了源区各冻土区植被的差异. 结果显示：总体上低温多年冻土区植被盖度、多样性指数高,表现为连续多年冻土区（查拉坪）>不连续多年冻土区（麻多乡）>季节冻土区（鄂陵湖北岸）,其中岛状多年冻土区（扎陵湖南岸）例外,该场地平均盖度最低,多样性指数介于查拉坪和麻多乡之间,局部植被退化较严重. 均匀度指数均表现为扎陵湖南岸最高,查拉坪次之. 地上生物量调查结果显示：查拉坪>麻多乡>扎陵湖南岸>鄂陵湖北岸,且鄂陵湖北岸出现指示植被退化的植物. 尽管黄河源区高寒植被研究为理解冻土退化条件下的生态环境变化提供了一些基础数据,评估气候变化和冻土退化的生态和水文效应需要更系统的调查和监测研究.     

祁连山大通河源区冻土特征及变化趋势

大通河源区位于祁连山中东部, 属高山多年冻土区, 利用源区内冻土钻探及监测资料对源区冻土发育的基本特征及变化趋势进行了分析和探讨. 冻土地温分析表明, 源区冻土年平均地温随海拔的变化梯度约为3.82 ℃·km^-1, 且冻土地温与表层覆被条件关系密切. 盆地平原地带多年冻土厚度约为17~86 m, 且以海拔每上升100 m冻土厚度增加约10 m的梯度增加. 多年冻土活动层厚度受海拔地带性作用不显著, 更多地受局地因素的控制, 地表覆被条件成为其主要影响因素. 在气温升高以及人类活动日益增多的影响下, 源区冻土整体处于退化状态, 多年冻土年平均地温以0.0075 ℃·a^-1的速率上升.     

探地雷达在黑龙江漠河县城区冻土勘测中的应用

在气候变暖影响下, 多年冻土对人类活动的响应更加敏感, 以至加速退化. 冻土退化后带来的生态环境和工程建筑热稳定性问题也会更加明显. 以黑龙江省漠河县城区为例, 结合钻孔资料和温度监测数据, 应用探地雷达对城区中心以及周边的多年冻土分布特征进行了探测, 研究分析了城市化对多年冻土的热影响. 结果表明: 雷达波在漠河城区地层的传播速度为0.07~0.08 m·ns^-1, 探地雷达结果与钻孔、温度监测资料相一致, 能够较准确的确定融化深度、冻土类型、地层结构. 城区对冻土退化影响较大, 城区中心冻土退化严重, 探测范围(0~10 m)内无冻土存在; 城郊周围沼泽化湿地下部普遍发育含冰量较高的多年冻土, 人为扰动影响较小, 冻土上限较浅, 冻土热状况相对稳定. 随着漠河城区逐渐扩张, 拟建或在建市政工程大多将修建在城郊周围沼泽化湿地上, 人为活动不断增加势必会加速多年冻土退化, 但其长期热影响范围和程度还需深入研究.     

Spatial and Temporal Distribution and Variations in the Near-surface Soil Freezing Days across China, 1956-2006

Using surface soil daily minimum temperature from 845 meteorological stations across China, the long-term (1971-2000) mean and spatial distribution of the near-surface soil freezing days were estimated with annual values of the number of near surface soil freezing days. The time series for the number of freezing days were constructed and compared with air temperatures in the same period.Resultsshowed that long term mean value in the number of the near surface soil freezing days increased with the increasing latitudes and altitudes over China. Near-surface soils were frozen for more than 200 days in the Qinghai Tibet Plateau, northern Xinjiang and northeast of China. The boundaries of permafrost zones coincide with the contour of (220±10) days of near-surface soil freezing. Using the mean number of 15 days of near-surface soil freezing as criterion, we found that the southern boundary of seasonally frozen ground is around the 25°N line, and the regions south of 22°N are essentially unfrozen regions. The time series of the number of freezing days showed a significant linear trend with change with a slope of -0.22days/year over a period from 1956 through 2006. After the 1990s, the linear slope was up to -1.02 days / year, indicating that the rate of decrease in the number of near-surface soil freezing days has accelerated. Changes in the number of near surface soil freezing were in a negative correlation with air temperature, i.e., the number of near-surface soil freezing days decreases with increase in air temperature.Backgroundcolor represents the contour values of the departure of near-surface soil freezing days from the 1971-2000 mean; Black dashed line is the boundary of permafrost regions, red dashed line is the boundary between frozen and unfrozen ground regions in China     

Mapping exposure to snow in a developing African context: implications for human and livestock vulnerability in Lesotho

Alpine cryospheric hazards are becoming increasingly prominent under current global/regional climate change scenarios and receiving wide scientific coverage from, in particular, northern hemisphere mountain regions associated with glaciers, permafrost, and extensive seasonal snow cover. However, there is a general paucity of knowledge and attention on cryospheric hazards associated with mountain environments only occasionally/rarely impacted by heavy seasonal snowfalls or severe frost events, particularly those in developing and southern hemisphere regions. Prolonged snow cover in the Lesotho Highlands sometimes carries the consequence of human and livestock deaths owing to isolation and exposure in this developing region. We use daily Moderate Resolution Imaging Spectroradiometer snow cover images for the period 2003–2010, to establish the frequency, extent, and timing of snowfalls across Lesotho. In addition, a digital shape file containing the location, name, and district attributes of 2,016 villages across Lesotho was used to assist in the construction of a village exposure to snow index. A ranking system was applied to each village according to the seasonal duration of snow cover, and the accessibility and proximity to the nearest road. Snowfalls occur on average between 1 and 8 times per annum, with village exposure to snow (potential vulnerability) being generally low, particularly for the lowlands and Senqu River Valley. However, the study identifies that some high-altitude (>2,500 m) villages such as Thoteng, Letseng-la-Terae, and Mabalane are, on occasion, highly exposed to prolonged snow cover, and particularly so during the mid-snow season of July/August. We demonstrate the importance of applying spatiotemporal assessments on infrequent snow occurrences (which carry associated hazards) in developing mountain regions such as Lesotho, with implications to reduce livelihood risks through improved disaster preparedness and a well-informed, focused emergency response.     

气候变化情景下青藏工程走廊融沉灾害风险性区划研究

气候变暖会加剧青藏工程走廊多年冻土区融沉灾害的发生,威胁重大工程的安全运营. 选取冻土体积含冰量和活动层厚度变化量为指标,借助ArcGIS软件,采用融沉指数模型对青藏工程走廊融沉灾害做出了区划. 结果表明：在未来50 a,青藏工程走廊内融沉灾害在A1B和A2情景下主要为中高风险性,在B1情景下主要为中低风险性. 高风险区主要分布在楚玛尔河高平原、五道梁和开心岭等高温高含冰量冻土区.     

气候变化情景下青藏高原多年冻土活动层厚度变化预测

在人类活动和气候变暖的共同影响下, 浅层多年冻土近地表和活动层的热状况会发生显著的变化, 从而对生态环境、 水文、 工程等产生较大的影响. 以A1B, A2, B1气候变化情景模式为基础, 运用Stefan公式计算和预测了青藏高原多年冻土区活动层厚度的变化特征. 结果表明: 以羌塘盆地为中心, 青藏高原多年冻土活动层厚度向其四周不断增加, 多年冻土活动层厚度随着气温升高而增加. A1B 、 A2模式下活动层厚度变化大, 相对人类活动强度较小的B1模式活动层厚度变化较小. 到2050年时, A1B情景活动层厚度平均约为3.07 m, 相对于2010年活动层厚度约增加0.3~0.8 m; B1情景活动层厚度增加0.2~0.5 m; A2情景增加0.2~0.55 m. 到2099年, A1B情景活动层的平均厚度将约为3.42 m; A2情景将可达3.53 m; B1情景将可达2.93 m. 气候变暖将可能加深活动层, 百年后将大范围改变多年冻土的空间分布.     

东北多年冻土地区地基承载力对气候变化敏感性分析

近年来,中国东北多年冻土地区正处于显著的增温过程中。由此导致多年冻土逐渐退化,并严重影响到构筑物的稳定性。以0.05 ℃的年平均气温上升率为背景,采用带有相变的传热学有限元方法,对中国东北多年冻土地区不同初始气温条件和不同含冰量类型冻土的地基温度状况以及季节活动层厚度变化进行了模拟;利用温度场有限元数值试验结果和已有承载力试验数据分析了不同类型冻土地基的力学性质对气温变化敏感性,评估了气温变化对各类冻土地基承载力的影响。气候变化对多年冻土地区构筑物稳定性影响程度取决于两个环节：其一,冻土地基温度状况对气候变化的响应;其二,冻土地基力学性质对地基温度变化的敏感性。研究结果表明,冻土地基含冰量和温度状态对其承载力随气温变化的敏感性具有显著的影响。含土冰层地基承载力对气温变化最为敏感,气温变化对高温冻土地区浅层地基承载力以及桩-土冻结强度影响较大;而深基础桩端冻土地基承载力受气候变化影响相对较小。     

青藏公路下伏多年冻土的融化分析

基于青藏公路沿线高温冻土区和低温冻土区2组地温观测孔5 a的地温观测资料, 研究了路基下伏多年冻土的融化状态, 定量分析了进入路基下多年冻土内的热状况. 结果表明: 路基近地表地温明显高于对应天然地表下的地温, 路基近地表经历的融化期长于对应天然地表, 高温冻土区路基内已形成贯穿融化夹层;进入高温冻土区路基下伏多年冻土内的热收支处于持续不断的吸热状态, 进入低温多年冻土区的热收支也呈现出吸热明显大于放热的周期性变化;高温冻土区接近0℃的地温及其持续不断的热积累是引起下伏多年冻土不断融化的主要原因. 低温冻土区进入多年冻土的热积累暂时以增高地温耗热为主, 随着地温的增高, 低温冻土区也可能发生强烈的冻土融化.     

The Last Permafrost Maximum (LPM) map of the Northern Hemisphere: permafrost extent and mean annual air temperatures, 25–17 ka BP

This paper accompanies a map that shows the extent of permafrost in the Northern Hemisphere between 25 and 17 thousand years ago. The map is based upon existing archival data, common throughout the Northern Hemisphere, that include ice‐wedge pseudomorphs, sand wedges and large cryoturbations. Where possible, a distinction is made between areas with continuous permafrost and areas where permafrost is either spatially discontinuous or sporadic. The associated mean annual palaeo‐temperatures that are inferred on the basis of present‐day analogues increase understanding of the possible changes in permafrost extent that might accompany current global warming trends. Areas with relict permafrost and areas that were formerly exposed due to lower sea level (submarine permafrost) are also mapped. Mapping is mostly limited to lowland regions (areas approximately <1000 m a.s.l.). Striking features that appear from the map are (i) the narrow permafrost zone in North America, which contrasts with the broader LPM permafrost zone in Eurasia (that may be related to different snow thickness or vegetation cover), (ii) the zonal extent of former LPM permafrost (that may reflect sea‐ice distribution), which contrasts with the present‐day pattern of permafrost extent (especially in Eurasia) and (iii) the relatively narrow zones of LPM discontinuous permafrost (that may indicate strong temperature gradients).     

多年冻土区桩基竖向承载力的预报模型

通过多年冻土区大气温度与地温关系,得出季节冻结期和季节融化期地面温度,进一步确定季节冻结及季节融化深度。综合地面温度得出多年冻土厚度随时间变化的关系,将大气温度、地面温度、融冻层厚度及多年冻土厚度变化建立起与时间相关的联系方程。考虑大气温度变化分析桩土相互作用并建立桩土相互作用模型。综合联系方程、桩土分析模型及冻土地区建筑地基基础设计规范中的单桩竖向承载力公式,建立了联系大气温度、地面温度、季节融冻深度、多年冻土层厚度变化与桩基承载力的关系预报模型,为预测在设计使用年限内随着大气温度变化桩基的工作状况提供较为科学的依据。