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1.
The degradation of permafrost stability in China over the past 30 years is evaluated using a new, high-resolution near-surface air temperature reanalysis dataset. Results show that the permafrost extent clearly decreased by 22% from 1980 to 2010, that is, a loss of 12.684;104 km2. The degradation occurred not only in the transition regions between permafrost and seasonally frozen ground, but also and more importantly, in the interior of the permafrost regions. The degradation in the interior of permafrost regions accounted for 87% of the total degraded areas. The degradation occurred mainly during the 1980s to 1990s in the northeast permafrost area and the Qilian Mountains, and during the 1990s to 2000s in most areas of the Qinghai-Tibet Plateau (QTP). This degradation will have systemic impacts on engineered infrastructures in permafrost regions, the water balance, and the global carbon budget. A more robust physical model should be used to evaluate the permafrost thermal stability at finer resolution in the future. 相似文献
2.
Benjamin M. Jones Guido GrosseKenneth M. Hinkel Christopher D. ArpShane Walker Richard A. BeckJohn P. Galloway 《Geomorphology》2012,138(1):1-14
Pingos are circular to elongate ice-cored mounds that form by injection and freezing of pressurized water in near-surface permafrost. Here we use a digital surface model (DSM) derived from an airborne Interferometric Synthetic Aperture Radar (IfSAR) system to assess the distribution and morphometry of pingos within a 40,000 km2 area on the western Arctic Coastal Plain of northern Alaska. We have identified 1247 pingo forms in the study region, ranging in height from 2 to 21 m, with a mean height of 4.6 m. Pingos in this region are of hydrostatic origin, with 98% located within 995 drained lake basins, most of which are underlain by thick eolian sand deposits. The highest pingo density (0.18 km− 2) occurs where streams have reworked these deposits. Morphometric analyses indicate that most pingos are small to medium in size (< 200 m diameter), gently to moderately sloping (< 30°), circular to slightly elongate (mean circularity index of 0.88), and of relatively low height (2 to 5 m). However, 57 pingos stand higher than 10 m, 26 have a maximum slope greater than 30°, and 42 are larger than 200 m in diameter. Comparison with a legacy pingo dataset based on 1950s stereo-pair photography indicates that 66 may have partially or completely collapsed over the last half-century. However, we mapped over 400 pingos not identified in the legacy dataset, and identified only three higher than 2 m to have formed between ca. 1955 and ca. 2005, indicating that caution should be taken when comparing contemporary and legacy datasets derived by different techniques. This comprehensive database of pingo location and morphometry based on an IfSAR DSM may prove useful for land and resource managers as well as aid in the identification of pingo-like features on Mars. 相似文献
3.
The Eighth International Symposium on Permafrost Engineering was held in Xi’an,China,October 2009.The major topics discussed in the symposium included:permafrost engineering (involving design,construction and evaluation);mitigation of frost hazards in the regions affected by seasonally frozen ground;properties of frozen soils,model development and their applications;frost hazards and periglacial environments in mountain and plateau regions;climatic,environmental and cryospheric changes;and permafrost hydrology,cold regions water resources and land uses.The papers submitted to the symposium and lectures during the meeting represented some new developments of research on cold region engineering and environment.Here we summarized the works of the symposium in topics including:Permafrost engineering;General geocryology;Properties of frozen soils:model development and their applications;And climatic,environmental and cryospheric changes.During the symposium,the attendees pointed out that future studies should pay more attention to theoretical study and engineering mechanism study,and also on interaction between climate change and cold region environments and their engineering affects. 相似文献
4.
Soil temperature records obtained from the active layer above permafrost at a site in northern Alaska during autumn and winter have variance spectra inconsistent with a purely conductive heat-transfer system. Although conductive heat-transfer theory predicts that temperature fluctuations are attenuated with depth, sub-diurnal thermal variance at the 50-cm level, near the base of the active layer, exceeded that at the 10-cm level. Short segments of the temperature record were drawn from three distinct periods of soil-frost conditions: (1) at the maximum vertical development of the active layer in early autumn; (2) during frost penetration and the formation of a zero curtain in early winter; and (3) after freezeback of the active layer. The variance spectra of these time series show systematic seasonal transitions that reflect changing mechanisms of heat transfer. During the first and second periods, heat transfer by internal evaporation and condensation dominates at wavelengths in the diurnal range. The spectral traces are not strongly self-similar and the fractal dimensions indicate extreme space-filling, especially at deeper levels. Once the active layer is frozen, conductive heat transfer dominates, producing a trend toward self-similarity. Both the thermal variance and the fractal dimension decrease with depth in the frozen regime. [Key words: Alaska, active layer, coupled flow, fractal dimension, frozen ground, heat transfer, permafrost, soil freezing, spectral analysis, zero curtain.] 相似文献
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6.
气候变化下的祁连山地区近40 年多年冻土分布变化模拟 总被引：4，自引：1，他引：3
冻土是一种对气候变化极为敏感的土体介质,故气候的变化过程能反映和模拟冻土的分布及变化趋势。基于高程-响应模型,运用高分辨率的高程数据（DEM）、经度数据（Longitude）、纬度数据（Latitude）、年平均气温数据（MAAT）和气温垂直递减率数据（VLRT）对祁连山地区近40 年的多年冻土分布状况进行了数值模拟。分析表明：① 该高程-响应模型模拟的冻土范围和变化趋势与相关研究所引入逻辑回归模型的模拟结果基本一致。② 该模型模拟的1970s、1980s、1990s,2000s 的祁连山地区冻土分布面积分别为9.75×104 km2、9.35×104 km2、8.85×104 km2、7.66×104 km2。在这40 年中,冻土的分布范围呈现出明显减少的趋势。③ 从1970s 到1980s、1980s 到1990s、1990s 到2000s 三个时间段内,冻土分布范围的退缩速率分别为4.1%、5.3%、13.4%,其呈现逐渐增速的趋势,1990s 到2000s 出现了跳跃式增长。本研究可为分析长时间序列祁连山地区的多年冻土变化提供科学参考依据。 相似文献
7.
近30年来藏北高原湖泊变化对气候波动的响应 总被引：7，自引：1，他引：6
According to the analysis of the climate materials including the topographic map in 1975, the TM and CBERS satellite remote
sensing materials from the 1980s to 2005 as well as the air temperature, precipitation, evaporation rate, maximum depth of
snow and the biggest depth of frozen soil in the past 45 years, the water level area of four lakes at the southeast of Nagqu,
Tibet including Bam Co, Pung Co, Dung Co and Nuripung Co show a distinct trend of expansion in the past 30 years. In 2005,
the water level area of the above four lakes increased by 48.2 km2, 38.2 km2, 19.8 km2 and 26.0 km2 respectively compared to 1975, with the respective increase rate of 25.6%, 28.2%, 16.2% and 37.6%. That is closely related
to the warming and humidified climate change in the recent years such as rise of the air temperature, increase of the precipitation,
decrease of the evaporation rate and permafrost degradation.
Foundation: National Natural Science Foundation of China, No.40761005
Author: Bian Duo (1966–), Professor, specialized in application of remote sensing and GIS on environment. 相似文献
8.
The Rwenzori Mountains are a high alpine mountain chain, about 40 × 80 km in size, just north of the equator in the western branch of the East African Rift System in Africa. The central part of the mountain chain is located in Uganda, and the highest peak, the Margherita Peak with 5119 m, lies on the border to the Democratic Republic of Congo. Topography is very pronounced, with steeply incised valleys and clear glacial landforms in the upper part of the mountain chain. The Rwenzori Mountains are an unusually high mountain chain located in the extensional setting of the East African Rift System, and the large elevation poses a challenging problem for geodynamists to explain.We have used the landscape evolution model ULTIMA THULE, which combines hillslope diffusion, fluvial erosion, and glacial abrasion and is driven by a climate driver, simulating the variations in temperature, precipitation, and relief over several glacial cycles. With a simulation time of 800 ka, we test the hypothesis of climate-tectonic interactions on the uplift of the Rwenzori Mountains.Our results show that a moderate cooling of around 6° causes widespread glaciation of the high mountain regions as observed during the peak glacial phases, and that morphological processes degrading the landscape allow for a tectonic uplift rate of around 0.5 mm a− 1. 相似文献
9.
Permafrost distribution, or ground that remains frozen for at least 2 years, has been modeled using a combination of Geographic Information System (GIS) techniques, Digital Elevation Model (DEM) variables, and land cover in alpine regions of the world. In the Front Range, however, no such empirical models have been developed, and field data are restricted in spatial extent, but rock glaciers are in abundance. Here, I present a probabilistic logistic regression model that is based on topoclimatic information (elevation and aspect) for rock glaciers derived from U.S. Geological Survey (USGS) 10-m DEMs. Classes of land cover, obtained from an Enhanced Thematic Mapper Plus (ETM+) image classification, were assigned weights and were then multiplied by the regression results to refine estimates. The effectiveness of the model was evaluated by comparing mean probability scores with rock glacier activity categories, Mean Annual Air Temperature (MAAT) from climatic stations on Niwot Ridge, and Bottom Temperature of winter Snow (BTS) measurements, while a Monte Carlo simulation was used to detect uncertainty associated with the original DEM. Permafrost scores >50% covered about 8.9% (242 km2) of the study area (2722 km2) with the highest scores clustered around Longs and Rowe Peaks. Permafrost locations showed a strong correlation with rock glacier activity classes, the −1.0 °C MAAT isotherm, and BTS measurements less than −3.0 °C. The uncertainty analysis revealed that slight global differences exist between the original and error prone DEM; however, local variations in aspect caused the most uncertainty. These results indicate that the model accurately represents regional distribution of permafrost. Therefore, topoclimatic information from rock glaciers and land cover, when combined with an uncertainty analysis, can effectively be used to map the occurrence of Front Range permafrost, providing an imperative tool for cartographers, planners, and geocryologists. 相似文献
10.
Since 1974, flow releases from Long Draw Reservoir have increased annual peak flows on La Poudre Pass Creek, Colorado, from ~ 5.6 m3/s to > 8.4 m3/s. The creek drains 61 km2 and channel morphology varies from step-pool to pool-riffle. Comparison of five channel reaches along the creek to channel reaches along neighboring rivers without flow regulation indicates that channel width has increased by as much as a factor of three along La Poudre Pass Creek. Width-to-depth ratio has also increased, the bed material in step-pool channel reaches has coarsened, and residual pool volumes have increased in pool-riffle channel reaches. Pool-riffle channel reaches have undergone the greatest change in response to flow augmentation. Although discharge has increased consistently for all five channel reaches, morphologic response varies in relation to gradient and channel morphology, making it impractical to precisely predict a priori the magnitude of channel response to flow augmentation. 相似文献
11.
Combined observations of hourly soil temperature and electric potential, the latter converted to a relative index of soil-water solute concentration, yield information on the physical chemistry of near-surface frost effects. Solute concentration near the descending 0° C isotherm in the refreezing active layer above permafrost is divided into three distinct zones: (1) an ion-enriched zone in the unfrozen active layer that precedes the penetrating freezing front; (2) an ion-purified desorbed zone at the freezing front that is the source region of the downward-expelled ions and water; and (3) a hydrologically isolated subfreezing zone of enhanced solute concentration located above the freezing isotherm. High-frequency fluctuations superimposed on these general patterns are traceable to vapor migration driven by surface thermal fluctuations. These effects diminish at temperatures below about -0.4° C, as permeability decreases with soil-ice formation. The combined temperature-solute concentration time series is used to develop sorption curves for the frozen organic and mineral soils, and indicates that approximately half of the pore water present in the mineral soil at -0.4° C had not been converted to ice at -6° C. Gradual soil desiccation over winter appears to result from outward vapor diffusion, possibly through soil cracks. [Key words: Alaska, active layer, frozen ground, soil temperature, soil water, permafrost.] 相似文献
12.
Comparison of conceptual landscape metrics to define hillslope-scale sediment delivery ratio 总被引：5，自引：0，他引：5
The aim of this study was to evaluate four metrics to define the spatially variable (regionalised) hillslope sediment delivery ratio (HSDR). A catchment model that accounted for gully and streambank erosion and floodplain deposition was used to isolate the effects of hillslope gross erosion and hillslope delivery from other landscape processes. The analysis was carried out at the subcatchment (~ 40 km2) and the cell scale (400 m2) in the Avon-Richardson catchment (3300 km2), south-east Australia. The four landscape metrics selected for the study were based on sediment travel time, sediment transport capacity, flux connectivity, and residence time. Model configurations with spatially-constant or regionalised HSDR were calibrated against sediment yield measured at five gauging stations. The impact of using regionalised HSDR was evaluated in terms of improved model performance against measured sediment yields in a nested monitoring network, the complexity and data requirements of the metric, and the resulting spatial relationship between hillslope erosion and landscape factors in the catchment and along hillslope transects. The introduction of a regionalised HSDR generally improved model predictions of specific sediment yields at the subcatchment scale, increasing model efficiency from 0.48 to > 0.6 in the best cases. However, the introduction of regionalised HSDR metrics at the cell scale did not improve model performance. The flux connectivity was the most promising metric because it showed the largest improvement in predicting specific sediment yields, was easy to implement, was scale-independent and its formulation was consistent with sedimentological connectivity concepts. These properties make the flux connectivity metric preferable for applications to catchments where climatic conditions can be considered homogeneous, i.e. in small-medium sized basins (up to approximately 3000 km2 for Australian conditions, with the Avon-Richardson catchment being at the upper boundary). The residence time metric improved model assessment of sediment yields and enabled accounting for climatic variability on sediment delivery, but at the cost of greater complexity and data requirements; this metric might be more suitable for application in catchments with important climatic gradients, i.e. large basins and at the regional scale. The application of a regionalised HSDR metric did not increase data or computational requirements substantially, and is recommended to improve assessment of hillslope erosion in empirical, semi-lumped erosion modelling applications. However, more research is needed to assess the quality of spatial patterns of erosion depicted by the different landscape metrics. 相似文献
13.
青藏高原西部区域多年冻土分布模拟及其下限估算 总被引：3，自引：0，他引：3
准确评估青藏高原西部多年冻土的空间分布及多年冻土下限深度情况对该区地下水资源利用、生态环境保护有重要意义.本文依托科技基础性工作专项“青藏高原多年冻土本底调查”在该区及周边取得的冻土调查资料,利用遥感数据和扩展地面冻结数模型模拟了该区多年冻土的空间分布,调查区的模拟验证表明该方法有较高的精度.在此基础上,根据有限的地温实测资料建立了地温与位置、高程、坡向和太阳辐射的关系,并根据地温-下限关系估算了该区多年冻土下限深度的分布情况.研究表明,该区有多年冻土约占36.9%,季节冻土占57.5%,多年冻土主要分布在34°N~36.5°N范围的喀喇昆仑、西昆仑一带,季节冻土主要分布在塔里木盆地和34°N以南地区.阿里高原及以南是岛状多年冻土分布区域,其多年冻土分布面积少于此前出版的冻土图所绘制的.青藏高原西部区域的多年冻土下限深度整体表现为由东南-西北逐渐加深. 相似文献
14.
The paper presents the sediment budget of the Isábena basin, a highly dynamic 445-km2 catchment located in the Central Pyrenees that is patched by highly erodible areas (i.e., badlands). The budget for the period 2007-2009 is constructed following a methodology that allows the interpolation of intermittent measurements of suspended sediment concentrations and enables a subsequent calculation of sediment loads. Data allow specification of the contribution of each subbasin to the water and sediment yield in the catchment outlet. Mean annual sediment load was 235,000 t y− 1. Specific sediment yield reached 2000 t km− 2 y− 1, a value that indicates very high sedimentary activity, especially in the case of Villacarli and Lascuarre subcatchments, were most badlands are located. The specific sediment yield obtained for the entire Isábena is 527 t km− 2 y− 1, a high value for such a mesoscale basin. Results show that a small part of the area (i.e., 1%) controls most of the catchment's gross sediment contribution. Sediment delivery ratio (ratio between sediment input from primary sources and basin export) has been estimated at around 90%, while in-channel storage represents the 5% of the annual load on average. The high connectivity between sediment sources (i.e., badlands) and transfer paths (i.e., streamcourses) exacerbates the influence of the local sediment production on the catchment's sediment yield, a quite unusual fact for a basin of this scale. 相似文献
15.
Although maps of active-layer thickness have useful roles in geocryology, polar ecology, and hydrology, a lack of geographically distributed data at appropriate scales has prevented their widespread implementation. The n-factor (ratio of temperature at the soil surface to that in the air) has considerable potential as a tool for mapping active-layer thickness and other geocryological parameters by providing refinements to relatively simple analytic solutions for the depth of thaw. Although temperature data from the soil surface under representative land-cover units have rarely been collected historically, recent advancements in data-logger technology allow the variability of soil-surface temperature regimes to be assessed inexpensively over small temporal and spatial intervals. Temperature data collected in the air at 2 m height and at the soil surface within 10 representative land-cover units in the Kuparuk River region of north-central Alaska were used to compute seasonal n-factor values for specific vegetation-soil associations. The resulting values were used with degree-day sums, a digital elevation model, and a digital map of vegetation to compute a modified Stefan estimate of thaw depth over a 26,278 km2 area. Comparisons between maps based on the n-factor and an empirical, data-intensive method show similar performance. Given sufficient ancillary data, the n-factor provides a useful tool for mapping active-layer thickness over large areas without intensive in situ data collection. [Key words: Alaska, permafrost, active-layer thickness, frozen ground, mapping, temperature.] 相似文献
16.
Characteristics of earth hummocks (pounus) with and without permafrost in Finnish Lapland 总被引：1，自引：0，他引：1
Finnish Lapland north of 68°30'N latitude is located in the zone of discontinuous permafrost. Two main types of permafrost have previously been found in northern Finland: palsas in the mires and frost in the bedrock on the barren fell summits. The aim of this study was (1) to investigate permafrost occurrence in the peaty earth hummocks (pounus) in several mires, and (2) model characteristics of pounus with and without permafrost.
This study showed that permafrost in Finnish Lapland occurs much more widely and commonly than was previously known. A total of 59% of the studied pounus were found to contain permafrost. Over 90% of the permafrost occurrence in the pounus was correctly classified in logistic regression modelling. The probability of permafrost in a pounu decreased with the height of vegetation, and increased with the pounu height and distance from the running stream. There were clear vegetation differences between pounus with and without permafrost. Unfrozen pounus are characterized by forest and mire species, whereas on the permanently frozen pounus the vegetation is patchier with species indicating drier conditions. Pounus provide an excellent object to study short–term and local variations in permafrost formation due to their small size. They react quickly to variation in temperature, snow depth and precipitation. We conclude that pounus can be classified as sporadic permafrost features in northernmost Europe under modern climatic conditions. 相似文献
This study showed that permafrost in Finnish Lapland occurs much more widely and commonly than was previously known. A total of 59% of the studied pounus were found to contain permafrost. Over 90% of the permafrost occurrence in the pounus was correctly classified in logistic regression modelling. The probability of permafrost in a pounu decreased with the height of vegetation, and increased with the pounu height and distance from the running stream. There were clear vegetation differences between pounus with and without permafrost. Unfrozen pounus are characterized by forest and mire species, whereas on the permanently frozen pounus the vegetation is patchier with species indicating drier conditions. Pounus provide an excellent object to study short–term and local variations in permafrost formation due to their small size. They react quickly to variation in temperature, snow depth and precipitation. We conclude that pounus can be classified as sporadic permafrost features in northernmost Europe under modern climatic conditions. 相似文献
17.
Wedge-like structures filled with silty sand penetrate Quaternary fluvial and aeolian sediments and, in places, Tertiary bedrock on the Ordos Plateau, North China. The wedges reflect thermal contraction cracking of either permafrost or seasonal frost during the Late Pleistocene and early Holocene. Wedges of about 1 m in depth form polygonal nets of 2-3 m in diameter(type B). They contrast with wedges of 3-4 m in depth that form polygons of 10-15 m in diameter(type A).This review focuses upon the highly variable size of the inferred polygon nets and discusses the problem of differentiating between seasonally and perennially frozen ground, or between seasonal frost and permafrost. 相似文献
18.
Monitoring vegetation and land use quality along the rural-urban gradient in a Mediterranean region 总被引：1，自引：0，他引：1
This paper illustrates a methodology to quantify vegetation quality and its possible degradation in a large ‘shrinking’ Mediterranean city. Vegetation quality was estimated at three years (1960, 1990, 2006) in the Nuts-3 prefecture of Rome, central Italy (5355 km2) through the analysis of comparable land cover maps. The aims of this work are to assess how ‘compact growth’ and ‘sprawl’ impact on vegetation quality, and to monitor the territorial disparities observed in the vegetation quality as caused by urbanization and land use polarization. Built-up areas covered 3.3% and 12.9% of the investigated area in 1960 and 2006, respectively, with a dispersed to compact urban surface ratio passing from 1.2 to 1.9. Vegetation quality increased slightly during the investigated period with a diverging trend between urban and rural areas. As a consequence, territorial disparities in the same variable grew due to low-density urban diffusion in lowlands and depopulation with land abandonment and natural forestation in mountain areas. 相似文献
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黄河源区冻土分布制图及其热稳定性特征模拟 总被引：5，自引：0，他引：5
以黄河源区多年冻土分布现状和热力特征为研究目标,通过野外调查及实测数据,分析了黄河源区不同地形地貌、不同地表覆盖条件下的冻土形成、分布特征和以地温为基础的热学特征,探讨了不同尺度因素对多年冻土分布的影响。结果表明,在高程低于4 300 m的平原区,多年冻土多不发育;在高于4 350 m的山区,局地地形对多年冻土的形成与分布作用显著。除阳坡地形外,多年冻土均比较发育;介于4 300~4 350 m的低山丘陵和平原区,局地地形、地表植被、土壤湿度等因素共同决定着多年冻土的形成和分布格局。以年均地温指标为基础,构建了以纬度、经度和高程为自变量的回归模型,并对阳坡地形进行微调和校正。结果表明,以0oC作为划分季节冻土和多年冻土的标准和界限,多年冻土面积2.5×104km2,约占整个源区面积的85.1%;季节冻土面积0.3×104km2,约占整个源区面积的9.7%。进一步以0.5oC或1.0oC为分类间隔绘制了黄河源区多年冻土热稳定性空间分布图。 相似文献