泛北极地区植被数据集与制图：回顾与展望

泛北极地区位于北半球高纬度地区,主要属于低温限制型生态系统,因而泛北极地区植被对全球变暖敏感。要明确泛北极地区陆地生态系统对全球变暖响应过程和机理,就需要高精度的植被类型分类数据作为基础资料。但是,目前泛北极地区植被数据的结果还不完善。为更好地认识泛北极地区植被类型分类的现状、发展历史和未来研究方向,本文综述了泛北极地区植被类型制图的数据来源、植被类型划分方法和植被类型制图研究方法。总体而言,泛北极地区的植被调查从20世纪20年代就陆续开展,目前部分区域尺度上的地表覆盖类型的结果,但具体的植被类型制图工作还存在一系列难题。主要原因包括植被野外调查实测数据较少和分布不均、植被类型分类标准不一、苔原植被群落的异质性大、制图技术和分类算法优化困难等。因此,在下一步泛北极植被类型制图工作中,需要制定标准化分类策略,规范数据获取及数据库的整理工作,并发展新的制图方法,从而促进植被类型制图研究工作。     

亚洲水塔 青藏高原

正它,横亘在亚洲中心,平均海拔4 000米以上,与周边地区有巨大的地势差,水汽拦截作用显著,是北极和南极之外最大的淡水储备库,是冰川、湖泊、多年冻土和江河源头的主要聚集区,是我国甚至亚洲水资源产生、赋存和运移的战略要地,被亲切地称为"亚洲水塔"。     

青藏铁路主要冻土路基工程热稳定性及主要冻融灾害

在介绍青藏高原多年冻土退化背景及其工程影响的基础上,通过主要冻土路基现场监测和沿线调查,对青藏铁路冻土路基2002年以来的地温发展过程、热学稳定性及次生冻融灾害进行了分析。结果表明:青藏铁路自2006年通车后冻土路基整体稳定,列车运行速度达100 km/h,达到设计要求,但不同结构路基的热学稳定性不同,采取"主动冷却"方法的路基稳定性显著优于传统普通填土路基。管道通风路基、遮阳棚路基及U型块石路基冷却下伏多年冻土的效果显著,块石基底路基左右侧对称性较差,而处于强烈退化冻土区和高温冻土区的普通路基热稳定性差,需结合路基所在区域局地气候因素予以调整或补强。以热融性、冻胀性及冻融性灾害为主的次生冻融灾害对路基稳定性存在潜在危害,主要表现为路基沉陷、掩埋、侧向热侵蚀等,其中目前最为严重的病害是以路桥过渡段沉降为代表的热融性灾害。     

解析地温场的主要影响因素

地温场是不均一的,许多因素都直接或间接地影响着地温场的分布。影响地温场的主要因素包括大地构造性质、基底起伏、岩浆活动、岩性、盖层褶皱、断层、地下水活动等。     

山东省地温梯度分布特征研究

在充分搜集山东省区域地质、构造地质、地热地质及地热遥感解译资料等基础上,开展了山东省地温场现状调查、1∶50万地热遥感解译和测温工作,根据收集资料程度,提出计算地温梯度的方法,计算了整个研究区地温梯度;评价了各个地热区地温梯度的分布规律,并从大地构造、基岩起伏、岩浆活动、地层岩性、断裂构造、地下水活动等方面分析了影响地温场分布的因素,讨论了浅部地温场与深部构造的关系,总结了研究区各区地温梯度的分布特征。     

冻土斜坡模型试验相似分析

南水北调工程、青藏铁路建设工程等一系列工程的实施,将进一步影响和加剧青藏高原多年冻土区斜坡稳定性问题,冻土区边坡开挖及斜坡稳定性是工程活动中必须解决的问题之一,冻土斜坡稳定性研究在国内尚属空白。通过相似模型试验对高原多年冻土区斜坡在自然和人类活动影响下的失稳机制和活动规律进行分析,是开展研究的重要手段。根据相似理论第一定律,对冻土斜坡模型试验进行了相似分析,应用积分类比法推导并建立了冻土斜坡模型试验的相似指标和相似判据,得出在用原状土作模型介质时,6个相似常数减少为2个相似常数,即cτ和cl。模型与原型的时间比例尺是由几何比例尺决定的,即cτ=c2l,仅有一个相似参数为自变量,另一个为因变量。据此对青藏高原多年冻土区青藏公路沿线K3035处冻土斜坡进行了相似模型设计和冻融模型试验。模型再现了K3035处7°斜坡在4个冻融循环条件下,坡体中部(水平、垂向)4#位移伸张计质点位移曲线随时间的变化特征。实验表明,斜坡土体中部在第一次冻融循环中已有滑动迹象,随着滑坎进一步后退和靠近观测基准点,必然出现一次较大的位移,直至周边土体出现滑塌为止。模型试验结果与现场观测资料相比较是令人满意的。     

南宁市浅层地温场特征及影响因素研究

南宁盆地内浅层地温能资源丰富,可作为未来经济发展的重要能源。文章通过对南宁浅层地温场特征进行分析,发现基底断裂尤其是心圩—韦村断裂构成了南宁盆地地热成生的导热通道,盆地北部地温梯度可达3.5℃/100m以上。盆地内第四系作为浅层地温能主要热储层,在富水和冲积层较厚的松散岩类孔隙水地区存在较高地温和地温梯度,而在南部的碳酸盐岩类裂隙溶洞水分布区,饱水岩土的地温梯度较小,在0.5℃/100m之下。除了构造作用影响外,在水动力条件控制下,常温带地温由盆地四周向盆地中心有升高的趋势,并且在地下水循环交替较快的南部碳酸盐岩地区,存在较高的导热系数。     

西安地区地温分布及地热异常分析

本文论述西安地区200、1000、2000及3000米深的地温分布及地温梯度的变化。划分了四个局部地热异常带,即秦岭北麓地热异常带、灞河地热异常带、西安市东南郊地热异常带及临潼地热异常带。 区域地温分布主要受以下因素控制:1.深部地壳结构控制区域地温场2.基底构造控制区域地温分布;3.活动性断裂系统对局部地热异常的形成有影响。 根据区域地温特征分析,地热异常的形成是以稍高地温梯度、传导传热的结果。浅部地质条件(断层、裂隙等),造成地温重新分配,使循环达一定深度的地下水加热产生局部对流。     

多年冻土区河流溶解性有机碳输出的研究进展

多年冻土区河流中溶解性有机碳（DOC）的输出对全球碳循环有着重要贡献,是全球气候变化研究的热点。当前研究主要集中在2个方面:多年冻土区河流DOC输出的时空特征及其影响因素;多年冻土区河流DOC输出对气候变暖和冻土退化的响应。研究表明,河流中DOC的浓度、通量、化学组分等主要受流域内水的流动路径、滞留时间及路径上潜在DOC源的特征控制,而多年冻土的分布及其季节性融冻循环对上述因素有显著影响,进而控制多年冻土区河流DOC的输出规律。气候变暖可从3个方面对多年冻土区河流DOC输出产生影响:①造成多年冻土退化,使地下水的流动路径变深和滞留时间增长,导致河流的DOC输出量降低;②使多年冻土中储存的老有机碳释放,导致河流的DOC输出量增高;③改善深部土壤的通气和温度条件,促进土壤微生物活性,进而影响河流DOC的输出量和化学特征。今后,有3个方面的研究需要加强:①中、低纬度高海拔冻土区河流DOC的输出规律及其与流域水文过程的关系;②小型源头河流DOC输出的对比与控制性试验;③冻土区地下水流过程的精细刻画和潜在有机碳源的直接探测。      

国际能源政治格局:一场没有硝烟的争夺战

北极圈能源前景广阔,俄罗斯率先打响争夺战近来,俄罗斯在北极地区的能源主张以及科考活动打破了北极固有的宁静,也让全世界的目光集中到了这里。北极丰富的能源储量无疑是引发北极争夺战的重要原因之一。参与北极圈争夺的五个国家包括俄、美、加拿大、丹麦和挪威。究竟是什么使众多国家对北极产生了兴趣?     

Thermal dynamics of the permafrost active layer under increased precipitation at the Qinghai-Tibet Plateau

Precipitation has a significant influence on the hydro-thermal state of the active layer in permafrost regions, which disturbs the surface energy balance, carbon flux, ecosystem, hydrological cycles and landscape processes. To better understand the hydro-thermal dynamics of active layer and the interactions between rainfall and permafrost, we applied the coupled heat and mass transfer model for soil-plant-atmosphere system into high-altitude permafrost regions in this study. Meteorological data, soil temperature, heat flux and moisture content from different depths within the active layer were used to calibrate and validate this model. Thereafter, the precipitation was increased to explore the effect of recent climatic wetting on the thermal state of the active layer. The primary results demonstrate that the variation of active layer thickness under the effect of short-term increased precipitation is not obvious, while soil surface heat flux can show the changing trends of thermal state in active layer, which should not be negligible. An increment in year-round precipitation leads to a cooling effect on active layers in the frozen season, i.e. verifying the insulating effect of "snow cover". However, in the thawed season, the increased precipitation created a heating effect on active layers, i.e. facilitating the degradation of permafrost. The soil thermal dynamic in single precipitation event reveals that the precipitation event seems to cool the active layer, while compared with the results under increased precipitation, climatic wetting trend has a different influence on the permafrost evolution.     

Symbiosis of marshes and permafrost in Da and Xiao Hinggan Mountains in northeastern China

Recently, the degradation of permafrost and marsh environments in the Da and Xiao Hinggan Mountains has become a great concern as more human activities and pronounced climate warming were observed during the past 30 years and projected for the near future. The distr/bution patterns and development mechanisms of the permafrost and marshes have been examined both in theories and in field observations, in order to better understand the symbiosis of permafrost and marshes. The permafrost and marshes in the Da and Xiao Hinggan Mountains display discernible zonations in latitude and elevation. The marsh vegetation canopy, litter and peat soil have good thermal insulation properties for the underlying permafrost, resulting in a thermal offset of 3 ℃ to 4℃ and subsequently suppressing soil temperature. In addition, the much higher thermal conductivity of frozen and ice-rich peat in the active layer is conducive to the development or in favor of the protection of permafrost due to the semi-conductor properties of the soils overlying the permafrost. On the other hand, because permafrost is almost impervious, the osmosis of water in marsh soils can be effectively reduced, timely providing water supplies for helophytes growth or germination in spring. In the Da and Xiao Hinggan Mountains, the permafrost degradation has been accelerating due to the marked climate warming, ever increasing human activities, and the resultant eco-environmental changes. Since the permafrost and marsh environments are symbiotic and interdependent, they need to be managed or protected in a well-coordinated and integrated way.     

Changes in the depths of seasonal freezing and thawing and their effects on vegetation in the Three-River Headwater Region of the Tibetan Plateau

Frozen ground degradation plays an important role in vegetation growth and activity in high-altitude cold regions. This study estimated the spatiotemporal variations in the active layer thickness(ALT) of the permafrost region and the soil freeze depth(SFD) in the seasonally frozen ground region across the Three Rivers Source Region(TRSR) from 1980 to 2014 using the Stefan equation, and differentiated the effects of these variations on alpine vegetation in these two regions. The results showed that the average ALT from 1980 to 2014 increased by23.01 cm/10 a, while the average SFD decreased by 3.41 cm/10 a, and both changed intensively in the transitional zone between the seasonally frozen ground and permafrost. From 1982-2014, the increase in the normalized difference vegetation index(NDVI)and the advancement of the start of the vegetation growing season(SOS) in the seasonally frozen ground region(0.0078/10 a, 1.83 d/10 a) were greater than those in the permafrost region(0.0057/10 a,0.39 d/10 a). The results of the correlation analysis indicated that increases in the ALT and decreases in the SFD in the TRSR could lead to increases in the NDVI and advancement of the SOS. Surface soil moisture played a critical role in vegetation growth in association with the increasing ALT and decreasing SFD. The NDVI for all vegetation types in the TRSR except for alpine vegetation showed an increasing trend that was significantly related to the SFD and ALT. During the study period, the general frozen ground conditions were favorable to vegetation growth, while the average contributions of ALT and SFD to the interannual variation in the NDVI were greater than that of precipitation but less than that of temperature.     

Changes in the thermal and hydraulic regime within the active layer in the Qinghai-Tibet Plateau

The change trends of air temperature,precipitation and evaporation from 1999 to 2008 shows that the climate in the Qinghai-Tibet Plateau permafrost region had become warmer.The analysis of the systematic active-layer data monitoring network along the Qinghai-Tibet Highway indicated that the active-layer thickness had been increasing and the soil temperature was rising.The soil temperature was rising in winter but not at the end of spring or during the entire summer.With thickening and warming of the active layer,the liquid water content of the active layer had an obvious downward migration and liquid water content in the top horizons decreased,but in the deeper horizons it increased.     

G317线汶川至马尔康段公路崩塌滑坡灾害危险性评估

为减少公路工程建设项目和地质灾害之间的相互影响,工程建设之前必须对工程建设用地存在的地质灾害进行评估。结合国道317线汶川至马尔康段公路改建工程的特点,对工程遭受或工程建设可能诱发加剧的滑坡和崩塌灾害发生的可能性作了分析,并提出相应的防治对策,为拟改建的公路建设提供指导性建议。     

Landslide distribution and sliding mode control along the Anninghe fault zone at the eastern edge of the Tibetan Plateau

Tibetan Plateau is known as the roof of the world. Due to the continuous uplift of the Tibetan Plateau, many active fault zones are present. These active fault zones such as the Anninghe fault zone have a significant influence on the formation of special geomorphology and the distribution of geological hazards at the eastern edge of the Tibetan Plateau. The Anninghe fault zone is a key part of the Y-shaped fault pattern in the Sichuan-Yunnan block of China. In this paper, high-resolution topographic data, multitemporal remote sensing images, numerical calculations, seismic records, and comprehensive field investigations were employed to study the landslide distribution along the active part of the Anninghe. The influence of active faults on the lithology, rock mass structures and slope stress fields were also studied. The results show that the faults within the Anninghe fault zone have damaged the structure and integrity of the slope rock mass, reduced the mechanical strength of the rock mass and controlled the slope failure modes. The faults have also controlled the stress field, the distribution of the plastic strain zone and the maximum shear strain zone of the slope, thus have promoted the formation and evolution of landslides. We find that the studied landslides are linearly distributed along the Anninghe fault zone, and more than 80% of these landslides are within 2-3 km of the fault rupture zone. Moreover, the Anninghe fault zone provides abundant substance for landslides or debris flows. This paper presents four types of sliding mode control of the Anninghe fault zone, e.g., constituting the whole landslide body, controlling the lateral boundary of the landslide, controlling the crown of the landslide, and constituting the toe of the landslide. The results presented merit close attention as a valuable reference source for local infrastructure planning and engineering projects.     

Modelling plant canopy effects on water-heat exchange in the freezingthawing processes of active layer on the Qinghai-Tibet Plateau

The effect of vegetation on the water-heat exchange in the freezing-thawing processes of active layer is one of the key issues in the study of land surface processes and in predicting the response of alpine ecosystems to climate change in permafrost regions. In this study, we used the simultaneous heat and water model to investigate the effects of plant canopy on surface and subsurface hydrothermal dynamics in the Fenghuoshan area of the QinghaiTibet Plateau by changing the leaf area index(LAI) and keeping other variables constant. Results showed that the sensible heat, latent heat and net radiation are increased with an increase in the LAI. However, the ground heat flux decreased with an increasing LAI. The annual total evapotranspiration and vegetation transpiration ranged from-16% to 9% and-100% to 15%, respectively, in response to extremes of doubled and zero LAI, respectively. There was a negative feedback between vegetation and the volumetric unfrozen water content at 0.2 m through changing evapotranspiration. The simulation results of soil temperature and moisture suggest that better vegetation conditions are conducive to maintaining the thermal stability of the underlying permafrost, and the advanced initial thawing time and increasing thawing rate of soil ice with the increase in the LAI may have a great influence on the timing and magnitude of supra-permafrost groundwater. This study quantifies the impact of vegetation change on surface and subsurface hydrothermal processes and provides a basic understanding for evaluating the impact of vegetation degradation on the water-heat exchange in permafrost regions under climate change.     

Different Responses of Vegetation to Frozen Ground Degradation in the Source Region of the Yellow River from 1980 to 2018

Frozen ground degradation under a warming climate profoundly influences the growth of alpine vegetation in the source region of the Qinghai-Tibet Plateau. This study investigated spatiotemporal variations in the frozen ground distribution, the active layer thickness(ALT) of permafrost(PF) soil and the soil freeze depth(SFD) in seasonally frozen soil from 1980 to 2018 using the temperature at the top of permafrost(TTOP) model and Stefan equation. We compared the effects of these variations on vegetation growth among different frozen ground types and vegetation types in the source region of the Yellow River(SRYR). The results showed that approximately half of the PF area(20.37% of the SRYR) was projected to degrade into seasonally frozen ground(SFG) during the past four decades; furthermore, the areal average ALT increased by 3.47 cm/yr, and the areal average SFD decreased by 0.93 cm/yr from 1980 to 2018. Accordingly, the growing season Normalized Difference Vegetation Index(NDVI) presented an increasing trend of 0.002/10 yr, and the increase rate and proportion of areas with NDVI increase were largest in the transition zone where PF degraded to SFG(the PF to SFG zone). A correlation analysis indicated that variations in ALT and SFD in the SRYR were significantly correlated with increases of NDVI in the growing season. However, a rapid decrease in SFD(-1.4 cm/10 yr) could have reduced the soil moisture and, thus, decreased the NDVI. The NDVI for most vegetation types exhibited a significant positive correlation with ALT and a negative correlation with SFD. However, the steppe NDVI exhibited a significant negative correlation with the SFD in the PF to SFG zone but a positive correlation in the SFG zone, which was mainly limited by water condition because of different change rates of the SFD.     

川藏公路海竹段地质灾害的遥感分析

本文重点是利用遥感地学分析原理研究了川藏公路海竹段的滑坡、崩塌和泥石流的地质灾害。同时 ,在遥感分析的基础上 ,对本区的工程地质进行了分区 ,为川藏公路改线及病害整治提供了基础资料.