Variability Of Active Layer Thickness Research Articles

A Physics-Based Compact DC Model for AOS TFTs Considering Effects of Active Layer Thickness Variation

A Physics-Based Compact DC Model for AOS TFTs Considering Effects of Active Layer Thickness Variation

Study on effect of different HTL and ETL materials on the perovskite solar cell performance with TCAD simulator

Perovskite solar cell (PSC) has gained lots of attention in the scientific community because of achieving high efficiency in a short period of time. The basic structure of PSC is the active layer sandwiched between the electron transport layer (ETL) and hole transport layer (HTL). Overall device performance depends on the materials of ETL and HTL. This research studied the effect of different ETL and HTL materials and the variation of active layer thickness on the PSC performance with the Sentaurus TCAD simulator. For HTL and ETL, two types of materials were used: organic and inorganic. Organic HTL material was spiro-OMeTAD, inorganic HTL material was NiOx, Organic ETL was PCBM, and inorganic ETL was SnO2. It was observed that inorganic ETL and organic HTL showed the best result for the specific active layer thickness, and the best result was PCE of 21.61%, Voc of 1.23 V, Jsc of 19.31 mA/cm2 and FF of 90%.

Perforated Turbostratic Graphene As Active Layer in a Nonvolatile Resistive Switching Memory Device

Perforated turbostratic graphene (PTG) sheets have been synthesized from a natural waste material, dead bougainvillea bracts, using a single-step pyrolysis method, and a resistive switching (RS) memory device has been constructed with it for the very first time. Herein, the edges of these large-area multilayer graphene sheets are highly conducting due to the turbostratic stacking between the adjacent layers of the graphene sheets. These highly conducting PTG sheets embedded inside an insulating polymer matrix can act as an active layer for resistive switching memory devices. This hybrid structure shows nonlinear resistance change between two distinct resistance states by simple bias voltage variation. The trap-assisted space-charge-limited conduction can realize the high resistive state (HRS), whereas the low resistive state (LRS) takes place through direct conduction. To achieve the best performing device, a number of optimizations have been performed, like the variation of polymer matrices, variation of PTG and polymer concentration, active layer thickness variation, and top electrode area variation. The best performing device showed reproducibility of current–voltage data (>200 cycles), low power consumption (SET voltage <1 V), a high ON/OFF ratio (>104), a long retention time (>104 s), and a large number of endurance cycles (>103). High writing-read-erase-read speed and flexibility/bending cycle tests were also carried out on the best-performing device to examine its tenacity. The current PTG-based flexible RS memory device derived from a biowaste, dead bougainvillea bracts, can provide an important step toward developing green electronics.

Spatial Variability of Active Layer Thickness along the Qinghai–Tibet Engineering Corridor Resolved Using Ground-Penetrating Radar

Active layer thickness (ALT) is a sensitive indicator of response to climate change. ALT has important influence on various aspects of the regional environment such as hydrological processes and vegetation. In this study, 57 ground-penetrating radar (GPR) sections were surveyed along the Qinghai–Tibet Engineering Corridor (QTEC) during 2018–2021, covering a total length of 58.5 km. The suitability of GPR-derived ALT was evaluated using in situ measurements and reference datasets, for which the bias and root mean square error were approximately −0.16 and 0.43 m, respectively. The GPR results show that the QTEC ALT was in the range of 1.25–6.70 m (mean: 2.49 ± 0.57 m). Observed ALT demonstrated pronounced spatial variability at both regional and fine scales. We developed a statistical estimation model that explicitly considers the soil thermal regime (i.e., ground thawing index, TIg), soil properties, and vegetation. This model was found suitable for simulating ALT over the QTEC, and it could explain 52% (R2 = 0.52) of ALT variability. The statistical model shows that a difference of 10 °C.d in TIg is equivalent to a change of 0.67 m in ALT, and an increase of 0.1 in the normalized difference vegetation index (NDVI) is equivalent to a decrease of 0.23 m in ALT. The fine-scale (&lt;1 km) variation in ALT could account for 77.6% of the regional-scale (approximately 550 km) variation. These results provide a timely ALT benchmark along the QTEC, which can inform the construction and maintenance of engineering facilities along the QTEC.

Thaw Settlement Monitoring and Active Layer Thickness Retrieval Using Time Series COSMO-SkyMed Imagery in Iqaluit Airport

Thaw consolidation of degrading permafrost is a serious hazard to the safety and operation of infrastructure. Monitoring thermal changes in the active layer (AL), the proportion of the soil above permafrost that thaws and freezes periodically, is critical to understanding the conditions of the top layer above the permafrost and regulating the construction, operation, and maintenance of facilities. However, this is a very challenging task using ground-based methods such as ground-penetrating radar (GPR) or temperature sensors. This study explores the integration of interferometric measurements from high-resolution X-band Synthetic Aperture Radar (SAR) images and volumetric water content (VWC) data from SoilGrids to quantify detailed spatial variations in active layer thickness (ALT) in Iqaluit, the territorial capital of Nunavut in Canada. A total of 21 SAR images from COSMO Sky-Med (CSK) were first analyzed using the freely connected network interferometric synthetic aperture radar (FCNInSAR) method to map spatial and temporal variations in ground surface subsidence in the study area. Subsequently, we built an ALT retrieval model by introducing the thaw settlement coefficient, which takes soil properties and saturation state into account. The subsidence measurements from InSAR were then integrated with VWC extracted from the SoilGrids database to estimate changes in ALT. For validation, we conducted a comparison between estimated ALTs and in situ measurements in the airport sector. The InSAR survey identifies several sites of ground deformation at Iqaluit, subsiding at rates exceeding 80 mm/year. The subsidence rate changes along the runway coincide with frost cracks and ice-wedge furrows. The obtained ALTs, ranging from 0 to 5 m, vary significantly in different sediments. Maximum ALTs are found for rock areas, while shallow ALTs are distributed in the till blanket (Tb), the intertidal (Mi) sediments, and the alluvial flood plain (Afp) sediment units. The intersection of taxiway and runway has an AL thicker than other parts in the glaciomarine deltaic (GMd) sediments. Our study suggests that combining high-resolution SAR imagery with VWC data can provide more comprehensive ALT knowledge for hazard prevention and infrastructure operation in the permafrost zone.

Spatial variability and influential factors of active layer thickness and permafrost temperature change on the Qinghai-Tibet Plateau from 2012 to 2018

Due to the complex topography and localized climate, active layer thickening and permafrost warming varied distinctly in different regions on the Qinghai-Tibet Plateau (QTP). Based on the borehole-temperature data at 93 sites from 2012 to 2018, we analyzed the temporal and spatial characteristics of active layer thickness, permafrost temperature, and relevant climatic factors in 8 typical geomorphological units on the QTP. The active layer thickened at 86 sites and thinned at 7 sites. The permafrost warmed at 89 sites and cooled at 4 sites. The median values of the annual increase rate of active layer thickness were from 0.04 to 0.13 m/a for the monitored regions. The highest rate reached 0.46 m/a, indicating severe permafrost degradation in local areas. The mean annual soil temperatures at a 6-m depth generally increased faster for cold permafrost, and the active layer thickened more significantly in warm permafrost sites. Among these regions, Kekexili Mountains showed a lower increase rate of active layer thickness, and the temperature rise of permafrost in the Fenghuoshan Mountains was more significant. The temporal change of snow cover duration was closely related to the active layer thickness variation in the northern permafrost regions on the QTP (Kunlunshan Mountains and Chumaerhe High Plain). In contrast, the temporal variation of freezing index was the dominant factor in the southern regions (Wuli Basin, Tongtianhe Basin, and Tanggula Mountains). No linear correlation between the temporal variations of climatical factors and active layer thickness variation was found for the regions in the middle of QTP (Kekexili Mountains, Beiluhe Basin, and Fenghuoshan Mountains ). The comprehensive effects of freezing index and snow cover duration result in the different relationships between air temperature variation and permafrost change in different regions on the QTP. These findings are beneficial for understanding the relationship between climate change and permafrost evolution.

Active Layer Thickness Variation on the Qinghai‐Tibetan Plateau: Historical and Projected Trends

AbstractAs the buffer layer between the atmosphere and permafrost, the active layer is vulnerable to climate change. The variation in the active layer thickness (ALT) has important effects on surface energy balance, ecosystem, hydrological cycle, vegetation cover, and engineering construction in permafrost regions. The goal of this study is to discuss the active layer variation under different shared socioeconomic pathways (SSPs) for specific warming levels and to reveal the potential interactions between the ALT and the associated driving factors in typical hydrological basins. We revised the Stefan solution using the edaphic factor and the thawing index calculated by multimodel data from the Coupled Model Intercomparison Project Phase 6 to estimate the variation in the ALT. During 2015 to 2100, the ALT will increase by 14 cm (SSP1‐2.6), 43 cm (SSP2‐4.5), and 1.44 m (SSP5‐8.5), with average increase rates of 2.5 cm/decade, 5.8 cm/decade, and 17.5 cm/decade, respectively. The rates of increase of the ALT in the Hexi basin, Inner basin, Mekong basin, Yangtze basin, and Yellow basin are 12.6 cm/decade, 6.7 cm/decade, 5.2 cm/decade, 8.0 cm/decade, and 5 cm/decade, respectively. These results illustrate that air temperature is the primary determinant of ALT variation and normalized difference vegetation index (NDVI) and snow depth may influence the ALT change. The most significant correlations are between the ALT and NDVI in the Yangtze basin. In different seasons, the spring snow depth has the greatest impact on the ALT in the Hexi basin.

Effect of active layer thickness variation on scaling response in a-IGZO thin film transistors under Schottky limited operation

Active layer thickness variation in highly-doped amorphous indium-gallium-zinc oxide thin film transistors with molybdenum-chromium contacts is studied to reveal parametric dependencies under both channel length and gate-contact overlap length scaling. Devices with thickness variations from 5 nm to 30 nm, channel length variation from 3 µm to 100 µm and gate-contact overlap length variation from 1 µm to 10 µm were fabricated, characterized and analyzed. Analysis from a field effect transistor perspective show typical thickness variation trends where threshold voltage shifts positively, subthreshold slope improves and I on/I off ratio increases as the active layer thickness is scaled down. Peculiar observations like extremely low saturation voltage, insensitivity towards channel length variations, two different slopes in the subthreshold region and peaks in the transconductance characteristics can be explained only by invoking the principle of Schottky transistor operation. Thinner devices exhibit high field Schottky operation with barrier lowering which causes monotonously increasing transconductance, while thicker devices show low field behavior with no barrier lowering signified by peaks with saturated behavior of transconductance. Channel length modulates this dependence of transconductance on thickness. Sensitivity towards gate-contact overlap length scaling increases with thickness. Devices with active layer thickness of 5 nm can withstand overlap length scaling up to 5 µm without transconductance degradation, while devices of 10 nm thickness can withstand overlap length scaling only upto 10 µm. Devices of 30 nm thickness show contact limited operation even at 10 µm overlap length. Conventional FET operating principles cannot explain these observations and the phenomenon of Schottky contact transistor operation has been invoked. The results point towards a thin borderline in low dimensional transistors, differentiating a FET from Schottky contact transistors, through a field dependent barrier lowering mechanism, which is modulated by active layer thickness, channel length and gate contact overlap length.

Permafrost thaw and ground settlement considering long-term climate impact in northern Alaska

Alaska’s North Slope is predicted to experience twice the warming expected globally. When summers are longer and winters are shortened, ground surface conditions in the Arctic are expected to change considerably. This is significant for Arctic Alaska, a region that supports surface infrastructure such as energy extraction and transport assets (pipelines), buildings, roadways, and bridges. Climatic change at the ground surface has been shown to impact soil layers beneath through the harmonic fluctuation of the active layer, and warmer air temperature can result in progressive permafrost thaw, leading to a deeper active layer. This study attempts to assess climate change based on the climate model data from the fifth phase of the Coupled Model Intercomparison Project and its impact on a permafrost environment in Northern Alaska. The predicted air temperature data are analyzed to evaluate how the freezing and thawing indices will change due to climate warming. A thermal model was developed that incorporated a ground surface condition defined by either undisturbed intact tundra or a gravel fill surface and applied climate model predicted air temperatures. Results indicate similar fluctuation in active layer thickness and values that fall within the range of minimum and maximum readings for the last quarter-century. It is found that the active layer thickness increases, with the amount depending on climate model predictions and ground surface conditions. These variations in active layer thickness are then analyzed by considering the near-surface frozen soil ice content. Analysis of results indicates that thaw strain is most significant in the near-surface layers, indicating that settlement would be concurrent with annual thaw penetration. Moreover, ice content is a major factor in the settlement prediction. This assessment methodology, after improvement, and the results can help enhance the resilience of the existing and future new infrastructure in a changing Arctic environment.

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.

Thermal effects of lateral supra‐permafrost water flow around a thermokarst lake on the Qinghai–Tibet Plateau

AbstractBoth the inflow and outflow of supra‐permafrost water to lakes play important roles in the hydrologic process of thermokarst lakes. The accompanying thermal effects on the adjacent permafrost are required for assessing their influences on the development of thermokarst lakes. For these purposes, the lake water level, temperature dynamics, and supra‐permafrost water flow of a lake were monitored on the Qinghai‐Tibet Plateau. In addition, the spatial and temporal variation of the active layer thickness and permafrost distribution around the lake were investigated by combining ground penetrating radar, electrical resistivity tomography, and borehole temperature monitoring. The results revealed that the yearly unfrozen supra‐permafrost water flow around the lake lasted approximately 5 months. The temperature and water level measurements during this period indicate that the lake water was recharged by relatively colder supra‐permafrost water from the north‐western lakeshore and was discharged through the eastern lakeshore. This process, accompanied by heat exchange with the underlying permafrost, might cause a directional difference of the active layer thickness and permafrost characteristics around the lake. Specifically, the active layer thickness variation was minimal, and the ice‐rich permafrost was found adjacent to the lakeshore along the recharge groundwater pathways, whereas a deeper active layer and ice‐poor permafrost were observed close to the lakeshore from which the warm lake water was discharged. This study suggests that the lateral flow of warm lake water can be a major driver for the rapid expansion of thermokarst lakes and provides clues for evaluating the relationships between the thermokarst expansion process and climate warming.

Internal structure of two alpine rock glaciers investigated by quasi-3-D electrical resistivity imaging

Abstract. Interactions between different formative processes are reflected in the internal structure of rock glaciers. Therefore, the detection of subsurface conditions can help to enhance our understanding of landform development. For an assessment of subsurface conditions, we present an analysis of the spatial variability of active layer thickness, ground ice content and frost table topography for two different rock glaciers in the Eastern Swiss Alps by means of quasi-3-D electrical resistivity imaging (ERI). This approach enables an extensive mapping of subsurface structures and a spatial overlay between site-specific surface and subsurface characteristics. At Nair rock glacier, we discovered a gradual descent of the frost table in a downslope direction and a constant decrease of ice content which follows the observed surface topography. This is attributed to ice formation by refreezing meltwater from an embedded snow bank or from a subsurface ice patch which reshapes the permafrost layer. The heterogeneous ground ice distribution at Uertsch rock glacier indicates that multiple processes on different time domains were involved in the development. Resistivity values which represent frozen conditions vary within a wide range and indicate a successive formation which includes several advances, past glacial overrides and creep processes on the rock glacier surface. In combination with the observed topography, quasi-3-D ERI enables us to delimit areas of extensive and compressive flow in close proximity. Excellent data quality was provided by a good coupling of electrodes to the ground in the pebbly material of the investigated rock glaciers. Results show the value of the quasi-3-D ERI approach but advise the application of complementary geophysical methods for interpreting the results.

Spatial variability of active layer thickness detected by ground‐penetrating radar in the Qilian Mountains, Western China

AbstractThe active layer plays a key role in geomorphic, hydrologic, and biogeochemical processes in permafrost regions. We conducted a systematic investigation of active layer thickness (ALT) in northeastern Qinghai‐Tibetan Plateau by using ground‐penetrating radar (GPR) with 100 and 200 MHz antennas. We used mechanical probing, pit, and soil temperature profiles for evaluating ALT derived from GPR. The results showed that GPR is competent for detecting ALT, and the error was ±0.08 m at common midpoint co‐located sites. Considerable spatial variability of ALT owing to variation in elevation, peat thickness, and slope aspect was found. The mean ALT was 1.32 ± 0.29 m with a range from 0.81 to 2.1 m in Eboling Mountain. In Yeniu Gou, mean ALT was 2.72 ± 0.88 m and varied from 1.07 m on the north‐facing slope to 4.86 m around the area near the lower boundary of permafrost. ALT in peat decreased with increasing elevation at rates of −1.31 m/km (Eboling Mountain) and −2.1 m/km (Yeniu Gou), and in mineral soil in Yeniu Gou, the rate changed to −4.18 m/km. At the same elevation, ALT on the south‐facing slope was about 0.8 m thicker than that on the north‐facing slopes, while the difference was only 0.18 m in peat‐covered area. Within a 100 m2 area with a local elevation difference of 0.8 m, ALT varied from 0.68 m to 1.25 m. Both field monitoring and modeling studies on spatial ALT variations require rethinking of the current strategy and comprehensive design.

Soil moisture redistribution and its effect on inter-annual active layer temperature and thickness variations in a dry loess terrace in Adventdalen, Svalbard

Abstract. High-resolution field data for the period 2000–2014 consisting of active layer and permafrost temperature, active layer soil moisture, and thaw depth progression from the UNISCALM research site in Adventdalen, Svalbard, is combined with a physically based coupled cryotic and hydrogeological model to investigate active layer dynamics. The site is a loess-covered river terrace characterized by dry conditions with little to no summer infiltration and an unsaturated active layer. A range of soil moisture characteristic curves consistent with loess sediments is considered and their effects on ice and moisture redistribution, heat flux, energy storage through latent heat transfer, and active layer thickness is investigated and quantified based on hydro-climatic site conditions. Results show that soil moisture retention characteristics exhibit notable control on ice distribution and circulation within the active layer through cryosuction and are subject to seasonal variability and site-specific surface temperature variations. The retention characteristics also impact unfrozen water and ice content in the permafrost. Although these effects lead to differences in thaw progression rates, the resulting inter-annual variability in active layer thickness is not large. Field data analysis reveals that variations in summer degree days do not notably affect the active layer thaw depths; instead, a cumulative winter degree day index is found to more significantly control inter-annual active layer thickness variation at this site. A tendency of increasing winter temperatures is found to cause a general warming of the subsurface down to 10 m depth (0.05 to 0.26 °C yr−1, observed and modelled) including an increasing active layer thickness (0.8 cm yr−1, observed and 0.3 to 0.8 cm yr−1, modelled) during the 14-year study period.

Soil organic carbon stocks in permafrost-affected soils in West Greenland

Little is known about soil organic carbon (SOC) stocks in permafrost-affected soils in Greenland. Generally, occurrence and stocks of SOC in permafrost-affected soils of the Arctic were underestimated for many years. Compared to the assumed dimension of the influence of carbon dynamics on climate change this knowledge should be substantially widened. A total of 155 soil samples were used to get a better understanding about SOC stocks, depth function and spatial distribution of SOC in permafrost-affected soils in a characteristic deglaciated valley in West Greenland southeast of Kangerlussuaq. The valley is characterized by a high variability of active layer thickness and pedo-variance mainly caused by topography.The average SOC stock of the Umimmalissuaq valley is 9.9kgm−2 in the upper 30cm and around 30kgm−2 in the first meter, which is remarkably higher than regional predictions with 6–15.9kgm−2 in the first 100cm. To account for spatial heterogeneity landscape units are developed which are most useful for grouping and predicting SOC stocks. The SOC store measured 14.2kgm−2 in the upper 30cm, 11.5kgm−2 on north-facing slopes, and 8.4kgm−2 on south-facing slopes. Little SOC stocks with around 6kgm−2 were found under abrasion fields particularly on hilltops and moraine ridges. Soils on south-facing slopes usually have very low SOC stocks in deeper soil horizons except of organic rich horizons in rarely occurring paleosols. North-facing soils and valley bottom slopes generally have high SOC stocks of around 19kg SOC m−2 in soil horizons with a depth of 30–100cm.In general, the main influencing parameter on SOC stocks is the soil organic matter input from the vegetative cover. The vegetative cover is mainly a result of topographic position and aspect related to the ice margin and katabatic winds. Soil moisture and high active layer may influence SOC stocks positively.

A SPATIO-TEMPORAL FRAMEWORK FOR MODELING ACTIVE LAYER THICKNESS

Abstract. The Arctic is experiencing an unprecedented rate of environmental and climate change. The active layer (the uppermost layer of soil between the atmosphere and permafrost that freezes in winter and thaws in summer) is sensitive to both climatic and environmental changes, and plays an important role in the functioning, planning, and economic activities of Arctic human and natural ecosystems. This study develops a methodology for modeling and estimating spatial-temporal variations in active layer thickness (ALT) using data from several sites of the Circumpolar Active Layer Monitoring network, and demonstrates its use in spatial-temporal interpolation. The simplest model’s stochastic component exhibits no spatial or spatio-temporal dependency and is referred to as the naïve model, against which we evaluate the performance of the other models, which assume that the stochastic component exhibits either spatial or spatio-temporal dependency. The methods used to fit the models are then discussed, along with point forecasting. We compare the predicted fit of the various models at key study sites located in the North Slope of Alaska and demonstrate the advantages of space-time models through a series of error statistics such as mean squared error, mean absolute and percent deviance from observed data. We find the difference in performance between the spatio-temporal and remaining models is significant for all three error statistics. The best stochastic spatio-temporal model increases predictive accuracy, compared to the naïve model, of 33.3%, 36.2% and 32.5% on average across the three error metrics at the key sites for a one-year hold out period.

Naphtho[1,2-b:5,6-b′]dithiophene Based Two-Dimensional Conjugated Polymers for Highly Efficient Thick-Film Inverted Polymer Solar Cells

Two-dimensional conjugated zigzag naphthodithiophene was used for construction of novel polymer photovoltaic materials. Two novel copolymers based on zigzag naphthodithiophene and alkylthieno[3,4-c]pyrrole-4,6-dione inserted with different alkyl substituted thiophene as bridges have been designed and synthesized (PzNDTT-TPD1 and PzNDTT-TPD2, respectively). The best power conversion efficiency of a PzNDTT-TPD1-based device reaches 7.50% at an active layer thickness of 203 nm and the device performances of PzNDTT-TPD1-based polymer solar cells are all above 6.4% with active layer thickness variations from 141 to 244 nm, suggesting that it is very suitable for the fabrication of high performance, large area solution-processed polymer solar cells.

Modelling and mapping climate change impacts on permafrost at high spatial resolution for an Arctic region with complex terrain

Abstract. Most spatial modelling of climate change impacts on permafrost has been conducted at half-degree latitude/longitude or coarser spatial resolution. At such coarse resolution, topographic effects on insolation cannot be considered accurately and the results are not suitable for land-use planning and ecological assessment. Here we mapped climate change impacts on permafrost from 1968 to 2100 at 10 m resolution using a process-based model for Ivvavik National Park, an Arctic region with complex terrain in northern Yukon, Canada. Soil and drainage conditions were defined based on ecosystem types, which were mapped using SPOT imagery. Leaf area indices were mapped using Landsat imagery and the ecosystem map. Climate distribution was estimated based on elevation and station observations, and the effects of topography on insolation were calculated based on slope, aspect and viewshed. To reduce computation time, we clustered climate distribution and topographic effects on insolation into discrete types. The modelled active-layer thickness and permafrost distribution were comparable with field observations and other studies. The map portrayed large variations in active-layer thickness, with ecosystem types being the most important controlling variable, followed by climate, including topographic effects on insolation. The results show deepening in active-layer thickness and progressive degradation of permafrost, although permafrost will persist in most of the park during the 21st century. This study also shows that ground conditions and climate scenarios are the major sources of uncertainty for high-resolution permafrost mapping.

Modelling and mapping permafrost at high spatial resolution in Wapusk National Park, Hudson Bay Lowlands1This article is one of a series of papers published in this CJES Special Issue on the theme ofFundamental and applied research on permafrost in Canada.2Earth Science Sector Contribution 20110058.

Most spatial modelling of permafrost distribution and dynamics has been conducted at half-degree latitude/longitude or coarser resolution. Such coarse results are difficult to use for land managers and ecologists. Here we mapped permafrost distribution at 30 m × 30 m resolution for a region in the northwest Hudson Bay Lowlands using a process-based model. Land-cover types and leaf area indices were derived from Landsat imagery; peat thickness was estimated from elevation based on field measurements; and climate data were interpolated from station observations. The modelled active-layer thickness and permafrost extent compared well with field observations, demonstrating that modelling and mapping permafrost at a high spatial resolution is practical for terrains such as these lowlands. The map portrayed large variations in active-layer thickness, with land-cover type and peat thickness being the most important controlling variables. The modelled active-layer thickness on average increased by 37% during the twentieth century due to increases in air temperature and precipitation, and permafrost disappeared in some southern areas. The spatial scale of the permafrost maps developed in this study is close to that of the ecosystem and landscape features; therefore, the results are useful for land management and ecosystem assessment.

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.