Permafrost distribution modelling in the mountains of the Mediterranean: Corral del Veleta,Sierra Nevada,Spain

A statistical model for automated mapping of the spatial distribution of permafrost in the area of Corral del Veleta in south-east Spain (3703' N, 322' W; 3398 m a.s.l.) was developed and applied. The model uses a relationship between permafrost occurrence as indicated by BTS measurements, and variables such as altitude, solar radiation and summer snow cover. The model was implemented within a geographical information system (GIS) and determines the spatial distribution of probable permafrost in Corral del Veleta. Validation was achieved by comparing the predicted permafrost distribution with the results of recent fieldwork, such as geomorphic mapping, geophysical soundings and ground temperature logging.     

Modelling alpine permafrost distribution,Val de Rechy,Valais Alps (Switzerland)

The spatial distribution of the alpine permafrost is modelled in the uppermost part of Val de Rechy (Valais Alps, Switzerland) with the use of a geographical information system (GIS). Two empirical-statistical models are compared and their validity tested by a set of bottom temperature of winter snow (BTS) measurements carried out in the field. One model can simulate the spatial distribution of the permafrost facing ground warming consecutive to climatic change. Local/regional maps of simulated permafrost distribution as presented in this paper can be useful in the context of a preventive approach for natural hazards management.     

Regional modelling of present,past and future potential distribution of discontinuous permafrost based on a rock glacier inventory in the Bagnes‐Hérémence area (Western Swiss Alps)

A regional model was used to draw the permafrost distribution in the 200 km 2 of the Bagnes-Hérémence area (Western Swiss Alps). The model is based on the fact that permafrost distribution depends mainly on altitude and orientation and that the minimal altitude of active/inactive rock glaciers can be used as an indicator of the lower limit of discontinuous permafrost. The lower limit of relict rock glaciers is also used as an indicator of past distribution of permafrost. An inventory of rock glaciers was therefore made in the study area. The lower limit of permafrost during the Younger Dryas was determined by comparing the position of relict rock glaciers and glacier extension during the Older Dryas. The model was then applied to four periods (Younger Dryas, Little Ice Age, current period and future) in order to show the temporal evolution of permafrost distribution and glacier extension.     

Numerical simulations of the influence of the seasonal snow cover on the occurrence of permafrost at high latitudes

It has repeatedly been reported that snow cover is a dominating factor in determining the presence or absence of permafrost in the discontinuous and sporadic permafrost regions. The temperature at the snow-soil interface by the end of winter, known as the bottom temperature of winter snow (BTS) method, has been used to detect the existence of permafrost in European alpine regions when the maximum snow depth is about 1.0 m or greater. A critical snow thickness of about 50 cm or greater can prevent the development of permafrost in eastern Hudson Bay, Canada. The objective of this study is to investigate the impact of snow cover on the presence or absence of permafrost in cold regions through numerical simulations. A one-dimensional heat transfer model with phase change and a snow cover regime is used to simulate energy exchange between deep soils and the atmosphere. The model has been validated against the in situ data in the Arctic. The simulation results indicate that both snow depth and the onset date of snow cover establishment are important parameters in relation to the presence or absence of permafrost. Early establishment of snow cover can make permafrost disappear, even with a relatively thin snow cover. Permafrost may survive when snow cover starts after the middle of December even with a snow thickness >1.0 m. This effect of snow cover on the ground thermal regime can be explained with reference to the pattern of seasonal temperature variation. Early establishment of snow cover enhances the insulating impact over the entire cold season, thus warming and eventually thawing the permafrost. The insulating effect is substantially reduced when snow cover starts relatively late and snowmelt in the spring creates a huge heat sink, resulting in a favorable combination for permafrost existence.     

Deep permafrost boreholes in western Svalbard,northern Sweden and southern Norway

The first deep permafrost boreholes (>10 m) ever drilled in Scandinavia for climatic studies constitute part of a transect of deep mountain permafrost boreholes through the mountains of Europe established under the EU PACE (Permafrost and Climate in Europe) Project. In Scandinavia, PACE boreholes are located at Juvvasshøe, southern Norway, Tarfalaryggen in northern Sweden, and northernmost in the transect at Janssonhaugen, western Svalbard. This paper outlines the aims and objectives of the PACE programme, and describes in detail the Svalbard and Scandinavian permafrost boreholes.     

Using relict rockglaciers in GIS-based modelling to reconstruct Younger Dryas permafrost distribution patterns in the Err-Julier area,Swiss Alp

Differences in mean annual air temperature between the Younger Dryas period and today were estimated at the fronts of 32 relict rockglaciers in the Err-Julier area, eastern Swiss Alps. The analyses were based on a case-by-case calculation of direct incoming solar radiation and mean annual air temperature using a digital elevation model (DEM) and meteo data of recent years. Our results suggest that mean annual air temperature during the Younger Dryas was lowered by c. 3C to 4C, and that the lower limit of permafrost occurrence was depressed considerably more than glacier equilibrium lines. This indicates strongly reduced precipitation (30% to 40% reduction) and much larger abundance of mountain permafrost at that time. A model simulation of the corresponding spatial permafrost distribution during the Younger Dryas indicates that glaciers in the study area were mostly surrounded by permafrost at that time and probably had a polythermal structure of englacial temperatures.     

GIS-simulation of the spatial distribution of snow cover and observed ground temperatures in the Daisetsu Mountains,Japan

This paper describes one geometrical method of simulating the spatial distribution of snow cover. Geographical Information Systems (GIS) and precise Digital Elevation Model (DEM) were used in the simulation. The model is based on empirical parameters called coefficients depending on slope aspect and inclination. As a result, this model predicts that windward convex terrains remain snow-free during winter. This snow cover distribution was validated by usage of an air photograph taken in early spring, and the distribution of vegetation patches which represent the outer fringes of snow covered areas. Low ground temperatures together with high DC resistivities, which suggest the presence of permafrost, were identified in simulated snow-free areas.     

Topographic radiation balance models: Sensitivity and application in periglacial geomorphology

Direct solar radiation integrated over one year is a function of latitude and time of year, and topographic slope , aspect and shadowing control the local distribution. Recently, several spatial models have been developed which estimate the radiation balance based on digital elevation models, taking into account aspect, slope and shadowing effects. For the periglacial realm, these models are integrated both in models estimating possible occurrence of mountain permafrost and in studies of active layer dynamics. In this article our aim is to assess and discuss sensitivity and validations of the radiation balance model SRAD, in comparison with two other topographic-based radiation models. The study site and field data are from Finse, Southern Norway.     

Investigation of mountain permafrost in the Kozia Dolinka valley,Tatra Mountains,Poland

The Kozia Dolinka valley lies at an altitude above 1900 m a.s.l. on the northern slope of the main ridge of the High Tatra Mountains. Mountain permafrost occurrences were studied with the use of BTS, infrared imaging, water and ground temperature measurements and DC resistivity soundings. The data suggest the existence of isolated patches of permafrost. The lowest observed bottom temperature of winter snow values was in the order of-10C. DC soundings revealed the existence of a high resistivity layer of limited extent. Permafrost seasonal monitoring was conducted with resistivity soundings. Measurements were carried out in spring-autumn 1999, when a distinct change in permafrost thickness was observed.     

Permafrost distribution in the Posets massif,Central Pyrenees

The Posets massif is located in the Central Pyrenees and reaches a height of 3363 m a.s.l. at the Posets peak, the second highest massif in the Pyrenees. Geomorphological maps of scales 1:25000 and 1:10000, BTS (bottom temperature of winter snow), ground measurements and snow poles were used to observe the more representative periglacial active landform association, ground thermal regime, the winter snow cover evolution and basal temperatures of snow. The main active periglacial landforms and processes related to the ground thermal regime and snow cover were studied. Mountain permafrost up to 2700 m a.s.l. on northexposed slopes and up to 2900 m a.s.l. on south-exposed slopes were detected. Three permafrost belts were differentiated: sporadic permafrost between 2700 and 2800 m a.s.l. and between 2850 and 3000 m a.s.l., discontinuous permafrost between 2800 and 2950 and between 2950 and 3050, and continuous permafrost up to 2900 m a.s.l. and up to 3050 m a.s.l. on northern and southern slopes, respectively.     

Permafrost dynamics in the north-east of European Russia at the end of the 20th century

In the major physiographic divisions of the north-east of European Russia, temperatures in the cryolithozone and the active/seasonally frozen layer were monitored during the period 1970 to 1995. Active layer depths increased on average by 11% to 15%, whereas the depths of the seasonally frozen layer decreased by 19% to 40%. The largest positive temperature increments, up to 1.2C, were characteristic for the piedmont and basement plains. Lacustrine-alluvial lowlands demonstrated oppositely directed temperature trends depending on a landform. Numerous sites with ongoing permafrost formation demonstrated negative temperature increments varying from 0.1C to 2.0C.     

Assessment of geomorphic hazards in connection with permafrost occurrence in the Zugspitze area (Bavarian Alps, Germany)

In the Zugspitze area (Bavarian Alps, Germany), permafrost conditions are present in limestone bedrock and in regolith. Distribution is strongly dependent on topography in the east–west oriented mountain crest with steep north- and south-facing slopes. Numerous structures mainly for tourist purposes (cable car and recreation buildings, ski-lift masts, rack-railway tunnel, tunnel with supply facilities) are situated in the area, and several of them are placed on ground with permafrost. Results from a temperature measurement programme and distribution modelling show that for some of these constructions, the effects of permafrost degradation have to be considered in terms of stability of the foundations.The permafrost limit is close to the summit crest, and therefore, stability evaluations for the constructions in this area have to bear in mind the possible warming or even melting of ice within the bedrock crevasses caused by climate warming. Stability of the foundations as well as stability of rock walls in this area will probably be affected by a shifting of the permafrost limit. Constructions in the Zugspitzplatt area are already affected by the melting ground ice, and stabilizing measures have to be evaluated for several foundations where subsidence is likely to occur.Besides the local results, the study provides for the first time data on permafrost distribution in the northern Alpine margin based on standard methods of BTS measurements and numerical modelling.     

积沙影响下伏冻土的水热耦合模型研究

青藏高原地区冻土正呈退化趋势,除气候变化、人为活动的影响外,沙漠化也被认为是冻土退化的原因之一,但仍存在较大争议。基于不饱和土渗流和热传导理论,结合CoLM和Coup-Model模型,初步构建了积沙-冻土-水热概念模型和耦合模型。并在两模型的基础上,讨论了沙层反射率、积沙体热容量、积沙体厚度和沙的传热率等参数对下伏冻土的热影响过程。结果表明,沙层的反射率、地面发射率均高于天然地表,沙层接受的热量较天然地表偏少;积沙地表下的沙层和活动层能截留更多热量,使冻结层获得的热量相对减少;沙的导热性较差,导致积沙地表下地温变化出现延迟,从而延缓冻土退化;同时,积沙无论厚薄,都将起到延缓冻土退化的作用。因而,沙漠化对青藏高原冻土退化的影响可能较小,但全面揭示沙漠化对冻土的影响仍需深入研究。     

黄河源区冻土分布制图及其热稳定性特征模拟

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。     

气候变化下的祁连山地区近40 年多年冻土分布变化模拟

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。     

Mountain permafrost distribution modeling using Multivariate Adaptive Regression Spline (MARS) in the Wenquan area over the Qinghai-Tibet Plateau

In high mountainous areas, the development and distribution of alpine permafrost is greatly affected by macro- and micro-topographic factors. The effects of latitude, altitude, slope, and aspect on the distribution of permafrost were studied to understand the distribution patterns of permafrost in Wenquan on the Qinghai-Tibet Plateau. Cluster and correlation analysis were performed based on 30 m Global Digital Elevation Model (GDEM) data and field data obtained using geophysical exploration and borehole drilling methods. A Multivariate Adaptive Regression Spline model (MARS) was developed to simulate permafrost spatial distribution over the studied area. A validation was followed by comparing to 201 geophysical exploration sites, as well as by comparing to two other models, i.e., a binary logistic regression model and the Mean Annual Ground Temperature model (MAGT). The MARS model provides a better simulation than the other two models. Besides the control effect of elevation on permafrost distribution, the MARS model also takes into account the impact of direct solar radiation on permafrost distribution.     

试论青藏高原多年冻土类型的划分

本文采用综合分析与主导因素相结合的原则，以干燥度作为主要指标并参考年降水量，年平均相对湿度及气温较差等，结合地形因素将青藏庙的多年冻土划分为：湿润，亚湿润，半干旱，干旱和极干旱５种类型，并对各类型代表性和冻土地区进行分别论述。     

Morphology and geotechnique of active-layer detachment failures in discontinuous and continuous permafrost, northern Canada

Fifty active-layer detachment failures triggered after forest fire in the discontinuous permafrost zone (central Mackenzie Valley, 65° N.) are compared to several hundred others caused by summer meteorological triggers in continuous permafrost (Fosheim Peninsula, Ellesmere Island, 80°N). Most failures fall into compact or elongated morphological categories. The compact type occur next to stream channels and have little internal disturbance of the displaced block, whereas the elongated types can develop on any part of the slope and exhibit greater internal deformation. Frequency distributions of length-to-width and length-to-depth ratios are similar at all sites. Positive pore pressures, expected theoretically, were measured in the field at the base of the thawing layer. Effective stress analysis could predict the instability of slopes in both areas, providing cohesion across the thaw plane was set to zero and/or residual strength parameters were employed. The location of the shear planes or zones in relation to the permafrost table and the degree of post-failure secondary movements (including headwall recession and thermokarst development within the failure track) differed between the localities, reflecting dissimilarity in the environmental triggers and in the degree of ground thermal disturbance.     

Channel network morphology and sediment dynamics under alternating periglacial and temperate regimes: a numerical simulation study

The occurrence of permafrost in a highly permeable catchment has a profound effect on runoff generation. The presence of permafrost effectively makes the subsoil impermeable. Therefore, overland flow can be the dominant runoff-generating process during periglacial conditions. The absence of permafrost will promote subsurface drainage and, therefore, saturation excess overland flow can become the dominant runoff-generating process during temperate conditions. In this paper, we present a numerical modelling study in which the effect of alternating climate-related phases of permafrost and nonpermafrost on catchment hydrology and geomorphology is investigated. Special attention is given to the characteristics of the channel network being formed, and the sediment yield from these catchments. We find that channel networks expand under permafrost conditions and contract under nonpermafrost conditions. A change from permafrost to nonpermafrost conditions is characterised by a decrease in sediment yield, while a change towards permafrost conditions is marked by a peak in sediment yield. This peak is explained by the build-up of a reservoir of erodible sediment during the nonpermafrost phase. The driving force behind this reservoir build-up may be local base-level change due to tectonic uplift or eustacy. We present a number of experiments, which show the details of this process. The results are in line with existing reconstructions of climate and fluvial dynamics during the Pleistocene in Europe and offer a new explanation to these observations.