Changes In Active Layer Thickness Research Articles

Permafrost on the Tibetan Plateau is degrading: Historical and projected trends

Permafrost degradation on the Tibetan Plateau (TP) will significantly affect local water cycle processes, downstream water ecology, and water security. In this study, we evaluate the long-term interannual dynamics of permafrost distribution and active layer thickness (ALT) on the TP based on historical data from Climatic Research Unit gridded Time Series (CRU TS) downscaling and projected data under four shared socio-economic pathways (SSPs) in Scenario Model Intercomparison Project (ScenarioMIP) of the Coupled Model Intercomparison Project Phase 6 (CMIP 6). To achieve this, we employ a data-driven scheme at 1 km resolution for both historical and future periods (1901–2100) that compares the performance of four machine learning algorithms to select the optimal algorithm for permafrost distribution and ALT simulations. Our results indicate that the permafrost on the TP has been undergoing degradation in both historical and future periods, with a decrease in permafrost area and an increase in ALT. The changing rates of permafrost area and regionally averaged ALT during the historical period (1901–2020) are −1.05 × 104 km2 decade–1 and 0.012 m decade–1, while an accelerated degradation is observed after the 1970 s (with changing rates of permafrost area and regionally average ALT of −3.62 × 104 km2 decade–1 and 0.055 m decade–1). Our results also suggested that permafrost degradation on the TP will continue in the future under the four SSP scenarios. The individual global climate models (GCMs) exhibit a consistent degradation trend but great uncertainty in degradation speed. The ensemble mean of simulations across 15 selected GCMs showed that the degradation percentage of permafrost area on the TP under scenarios SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5 was 26.0 ± 6.8 %, 50.4 ± 5.6 %, 79.2 ± 4.5 %, and 89.0 ± 4.0 % by 2100, and the regionally average ALT increased by 0.301 ± 0.112 m, 0.628 ± 0.113 m, 1.204 ± 0.119 m, and 1.486 ± 0.125 m, respectively. We also analyze permafrost stability and elevation-dependent changes of ALT on the TP. The permafrost stability increases with elevation and latitude, and ALT changes more intensely with increasing elevation. This study will provide valuable data for hydrological and ecological studies related to permafrost on the TP.

Response of active layer thickening to wildfire in the pan-Arctic region: Permafrost type and vegetation type influences

Northern high-latitude permafrost holds the largest soil carbon pool in the world. Understanding the responses of permafrost to wildfire is crucial for improving our ability to predict permafrost degradation and further carbon emissions. Recently, studies have demonstrated that wildfires in the pan-Arctic region induced the thickening of the active layer based on site or fire event observations. However, how this induced thickening is influenced by vegetation and permafrost types remains not fully understood due to the lack of wall-to-wall analysis. Therefore, this study employed remotely sensed fire data and modelled active layer thickness (ALT) to identify the fire-induced ALT change (ΔALT) for the pan-Arctic region, and the contributions of vegetation and permafrost were quantified using the random forest (RF) model. Our results showed that the average ΔALT and the sensitivity of ΔALT to burn severity both increased with decreasing ground ice content in permafrost. The largest values were detected in thick permafrost with low ground ice content. Regarding vegetation, the average and sensitivity of ΔALT in tundra were highest, followed by those in forest and shrub. When the individual environmental factors were all taken into account, the results showed that the contribution of vegetation types was much higher than that of permafrost types (20.2 % vs. 3.5 %). Our findings highlighted the importance of environmental factors in regulating the responses of permafrost to fire.

Changes in permafrost spatial distribution and active layer thickness from 1980 to 2020 on the Tibet Plateau

The Tibetan Plateau (TP) is experiencing extensive permafrost degradation due to climate change, which seriously threatens sustainable water and ecosystem management in the TP and its downstream areas. Understanding the evolution of permafrost is critical for studying changes in the water cycle, carbon flux, and ecology of the TP. In this study, we mapped the spatial distribution of permafrost and active layer thickness (ALT) at 1 km resolution for each decade using empirical models and machine learning methods validated with borehole data. A comprehensive comparison of model results and validation accuracy shows that the machine learning method is more advantageous in simulating the permafrost distribution, while the ALT simulated by the empirical model (i.e., Stefan model) better reflects the actual ALT distribution. We further evaluated the dynamics of permafrost distribution and ALT from 1980 to 2020 based on the results of the better-performing models, and analyzed the patterns and influencing factors of the changes in permafrost distribution and ALT. The results show that the permafrost area on the TP has decreased by 15.5 %, and the regionally average ALT has increased by 18.94 cm in the 2010s compared to the 1980s. The average decreasing rate of permafrost area is 6.33 × 104 km2 decade−1, and the average increasing rate of ALT is 6.31 cm decade−1. Permafrost degradation includes the decreasing permafrost area and the thickening active layer mainly related to the warming of the TP. Spatially, permafrost area decrease is more susceptible to occur at lower latitudes and lower altitudes, while ALT increases more dramatically at lower latitudes and higher altitudes. In addition, permafrost is more likely to degrade to seasonally frozen ground in areas with deeper ALT.

Interannual and seasonal variations of permafrost thaw depth on the Qinghai-Tibetan Plateau: A comparative study using long short-term memory, convolutional neural networks, and random forest.

An accurate estimation of thaw depth is critical to understanding permafrost changes due to climate warming on the Qinghai-Tibetan Plateau (QTP). However, previous studies mainly focused on the interannual changes of active layer thickness (ALT) across the QTP, and little is known about the changes in the seasonal thaw depth. Machine learning (ML) is a critical tool to accurately estimate the ALT of permafrost, but a direct comparison of ML with deep learning (DL) in ALT projection regarding the model performance is still lacking. Here, ML, namely random forest (RF), and DL algorithms like convolutional neural networks (CNN) and long short-term memory (LSTM) neural networks were compared to estimate the interannual changes of ALT and seasonal thaw depth on the QTP. Meteorological series, in-situ collected ALT observations, and geospatial information were used as predictors. The results show that both ML and DL methods are capable of estimating ALT and seasonal thaw depth in permafrost areas. The CNN and LSTM models developed using longer lagging times exhibit better performance in thaw depth prediction while the RF models are either mediocre or sometimes even worse as the lagging time increases. The results show that the ALT from 2003 to 2011 on the QTP exhibits an increasing trend, especially in the northern region. In addition, 68.8%, 88.7%, 52.5%, and 47.5% of the permafrost regions on the QTP have deepened seasonal thaw depth in spring, summer, autumn, and winter, respectively. The correlation between air temperature and permafrost thaw depth ranges from 0.65 to 1 with the time lag ranging from 1 to 32 days. This study shows that ML and DL can be effectively used in retrieving ALT and seasonal thaw depth of permafrost, and could present an efficient way to figure out the interannual and seasonal variations of permafrost conditions under climate warming.

Using a mechanistic model to explain the rising non-linearity in storage discharge relationships as the extent of permafrost decreases in Arctic catchments

• There is a progression in the value of hydraulic parameters as permafrost thaws. • The hydrologic response transforms as permafrost goes from continuous to absent. • The hillslope gradient can be the controlling influence of the catchment response. • The response is the result of the interaction of multiple interdependent processes. The relationship between groundwater and discharge in Arctic and sub-Arctic regions is strongly controlled by permafrost. Previous work has shown that catchments with thawing frozen soils due to the warming climate are expected to show changes in their storage-discharge relationship. In this study, we use a mechanistic modelling approach to demonstrate that a thawing catchment underlain with continuous permafrost undergoes a dramatic change in storage-discharge relationship. We demonstrate that the effect of permafrost thaw, conceptualized as a reduction of an impermeable layer in the subsurface, will likely only be clearly observable as a change in slope of the recession curve of catchments with hillslope gradients>5 %. For flat catchments (<1% hillslope gradient), we find no relation with permafrost extent and change in recession curve slope will likely be dominated by changes in active layer parameters, such as in shallow surface permeability (Hydraulic Conductivity, above permafrost) and shallow surface and subsurface water retention (Specific Yield of Groundwater & Specific Yield of Surface). For mildly sloped Arctic catchments (5 % hillslope gradient), change in recession curve slope is controlled both by changes in permafrost extent and the subsurface flow length and subsurface hydraulic properties for the shallow flow, with minimal impact from overland flow properties and changes in meteorological factors. For moderately sloped Arctic catchments (10 % hillslope gradient), change in recession curve slope change is dominated by changes in permafrost extent, and secondly by changes in the subsurface flow length and subsurface hydraulic properties, with no impact from meteorological factors or changes in overland flow properties. Several of the parameters found to be driving shifts in recession curve slopes in our modeling, such as changes in active layer thickness and the formation of taliks, are more likely than others to evolve with the ongoing Arctic climate change in hillslopes, helping us understand what drives the real-world increases in non-linearity of storage-discharge relationships.

Active Layer Thickness in the Northern Hemisphere: Changes From 2000 to 2018 and Future Simulations

AbstractActive layer dynamics are basic information for understanding permafrost degradation, but there are gaps in our knowledge of the active layer thickness (ALT) variations during the past two decades and their future changes; this is especially true for data with high spatial resolution. Here, based on permafrost monitoring data and ERA5 (the 5th generation reanalysis project from the European Centre for Medium‐Range Weather Forecasts)‐Land temperature data, we simulated spatial changes in ALT in the Northern Hemisphere during 2000–2018 at a spatial resolution of 1 km2 using the Stefan model. We also simulated future changes in the active layer based on the CMIP6 temperature data. The results showed that ALTs less than 50 cm were mainly distributed in northeastern Siberia in Russia, Alaska and Greenland. The areas with ALTs greater than 600 cm were mainly in southern Norway, and the Mongolian Plateau. The mean ALT of permafrost in the Northern Hemisphere from 2000 to 2018 increased from 127.19 to 145.37 cm at a linear rate of 0.65 cm year−1 (R2 = 0.37, p &lt; 0.05). During 2000–2018, the ALT increased in 71.17% of the total permafrost area, and only 27.23% of the permafrost area showed a decreasing trend. Under different shared socioeconomic pathways (SSP1‐2.6, SSP2‐4.5, SSP3‐7.0, and SSP5‐8.5), the ALT will increase considerably by 2,100. There is a greater increase in ALT in low‐ and mid‐latitude permafrost areas such as the Mongolian Plateau and Qinghai‐Tibet Plateau, with the ALT increasing from 50 to 500 cm. Our results present an overall picture of contemporary distribution as well as future changes of ALT in the Northern Hemisphere.

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.

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.

Changes in permafrost extent and active layer thickness in the Northern Hemisphere from 1969 to 2018

Understanding the evolutions of the permafrost extent and active layer thickness (ALT) in the Northern Hemisphere (NH) are critical for global carbon flux simulation, climate change prediction, and engineering risk assessment. The temporal change characteristics of the permafrost extent and ALT for the NH have not been studied. We used the Kudryavtsev method, integrating a 0.5° × 0.5° spatial resolution of air temperature, soil texture, snow depth, vegetation type, soil volume moisture content, and organic content to simulate the changes of permafrost extent and ALT in the NH from 1969 to 2018. The results indicated that permafrost extent decreased from 23.25 × 106 km2 (average from 1969 to 1973) to 21.64 × 106 km2 (average from 2014 to 2018), with a linear rate of −0.023 × 106 km2/a. Siberia had the highest degradation rate of 0.014 × 106 km2/a, followed by Alaska, Mongolian Plateau, Qinghai-Tibet Plateau, Northern Canada, and Greenland, with linear rates of −0.012 × 106, −0.005 × 106, −0.004 × 106, −0.0014 × 106, and − 0.0004× 106 km2/a, respectively. The average ALT in the NH increased at a linear rate of 0.0086 m/a. Alaska and Mongolian Plateau had the highest thickening rate of 0.024 m/a, followed by Qinghai-Tibet Plateau, Siberia, Northern Canada, and Greenland, which had linear rates of 0.009, 0.008, 0.0072, and 0.003 m/a, respectively. The uncertainty of the results could be attributed to the inaccurate forcing data and limitations of the Kudryavtsev model.

Modeling and mapping permafrost active layer thickness using field measurements and remote sensing techniques

Quantifying end of summer season Active Layer Thickness (ALT) of permafrost is critical for understanding the effects of climate warming, disturbance, and hydrologic changes on permafrost. Current research mainly focuses on ALT estimation and mapping at large scales using process-based or statistical-empirical models with biophysical variables as predictors. Here we modeled multi-year ALT field measurements between 2014 and 2019 at a site in Interior Alaska using 1-m hyperspectral imaging data and an object-based ensemble approach at a local scale (1 km2), examined the efficacy of the multispectral sensor WorldView (WV)-2 for ALT estimation, and explored the potential of integrating single-date imaging data with multi-year in-situ measurements for mapping the spatial and temporal variation of ALT. Modeling results showed hyperspectral imaging was accurate for estimating ALT with a correlation coefficient (r) larger than 0.7, while application of WV-2 data produced an r around 0.4. Reasonable ALT patterns were generated, and the spatial and temporal variation of ALT was delineated between the shallowest (2015) and deepest (2019) years using hyperspectral data. This study suggests hyperspectral imaging is a promising tool for predicting field ALT measurements and monitoring ALT change at local scales. We expect this study will stimulate hyperspectral optical sensors for permafrost studies in general, and particularly for ALT upscaling.

Simulation of the Present and Future Projection of Permafrost on the Qinghai‐Tibet Plateau with Statistical and Machine Learning Models

AbstractThe comprehensive understanding of the occurred changes of permafrost, including the changes of mean annual ground temperature (MAGT) and active layer thickness (ALT), on the Qinghai‐Tibet Plateau (QTP) is critical to project permafrost changes due to climate change. Here, we use statistical and machine learning (ML) modeling approaches to simulate the present and future changes of MAGT and ALT in the permafrost regions of the QTP. The results show that the combination of statistical and ML method is reliable to simulate the MAGT and ALT, with the root‐mean‐square error of 0.53°C and 0.69 m for the MAGT and ALT, respectively. The results show that the present (2000–2015) permafrost area on the QTP is 1.04 × 106 km2 (0.80–1.28 × 106 km2), and the average MAGT and ALT are −1.35 ± 0.42°C and 2.3 ± 0.60 m, respectively. According to the classification system of permafrost stability, 37.3% of the QTP permafrost is suffering from the risk of disappearance. In the future (2061–2080), the near‐surface permafrost area will shrink significantly under different Representative Concentration Pathway scenarios (RCPs). It is predicted that the permafrost area will be reduced to 42% of the present area under RCP8.5. Overall, the future changes of MAGT and ALT are pronounced and region‐specific. As a result, the combined statistical method with ML requires less parameters and input variables for simulation permafrost thermal regimes and could present an efficient way to figure out the response of permafrost to climatic changes on the QTP.

Simulated response of the active layer thickness of permafrost to climate change: 模拟多年冻土活动层厚度对气候变化的响应

The active layer thickness (ALT) in permafrost regions, which affects water and energy exchange, is a key variable for assessing hydrological processes, cold-region engineering, and climate change. In this study, the authors analyzed the variation trends and relative changes of simulated ALTs using the Chinese Academy of Sciences Land Surface Model (CAS-LSM) and the Chinese Academy of Sciences Flexible Global Ocean–Atmosphere–Land System Model, gridpoint version 3 (CAS-FGOALS-g3). Firstly, the simulated ALTs produced by CAS-LSM were shown to be reasonable by comparing them with Circumpolar Active Layer Monitoring observations. Then, the authors simulated the ALTs from 1979 to 2014, and their relative changes across the entire Northern Hemisphere from 2015 to 2100. It is shown that the ALTs have an increasing trend. From 1979 to 2014, the average ALTs and their variation trends over all permafrost regions were 1.08 m and 0.33 cm yr−1, respectively. The relative changes of the ALTs ranged from 1% to 58%, and the average relative change was 10.9%. The variation trends of the ALTs were basically consistent with the variation trends of the 2-m air temperature. By 2100, the relative changes of ALTs are predicted to be 10.3%, 14.6%, 30.1%, and 51%, respectively, under the four considered hypothetical climate scenarios (SSP-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5). This study indicates that climate change has a substantial impact on ALTs, and our results can help in understanding the responses of the ALTs of permafrost due to climate change.摘要在气候变化背景下, 活动层厚度的变化会对多年冻土区水文,生态,寒区工程等产生较大的影响.本研究利用中科院气候系统模式CAS-FGOALS-g3和陆面过程模式CAS-LSM 模拟分析了活动层厚度的变化趋势和相对变化.结果表明:活动层厚度整体上呈现出增加的趋势.1979 - 2014年, 多年冻土区活动层厚度的区域平均为1.08 m, 变化趋势为0.33 cm yr−1, 其变化趋势与2 m气温变化趋势基本一致, 相对变化范围为1%-58%, 平均为10.9%.在未来四种不同的气候情景(SSP-2.6,SSP2-4.5,SSP3-7.0和SSP5-8.5)下, 到2100年预计活动层厚度的相对变化分别为10.3%,14.6%,30.1%和51%.

Remote sensing spatiotemporal patterns of frozen soil and the environmental controls over the Tibetan Plateau during 2002–2016

The changing climate is affecting the frozen soil at an unprecedented rate across the Northern Hemisphere. However, due to sparse ground measurements, the changes of frozen soil and the environmental controls over the vast cryosphere are still unclear, such as in the Tibetan Plateau (TP). In this study, a process-based model solely driven by satellite remote sensing data is employed to investigate the spatiotemporal changes of seasonally frozen ground and permafrost over the entire TP (~3 million km2) during 2002–2016 at a spatial resolution of 1 km. Comprehensive validations against in situ observations of frozen ground types, mean annual ground temperature, active layer thickness, soil temperature, and frozen depth at 608 boreholes and 109 meteorological stations demonstrate an overall satisfactory performance of the model in reproducing the spatial pattern and temporal evolution of the frozen soil in the region. Spatially, land surface temperature (LST; both in-season and off-season) primarily controls the frozen ground types and frozen depth, with seasonally frozen ground and permafrost covering ~56% and ~ 37% of the plateau, respectively. The estimated spatial-averaged annual maximum soil freeze depth (SFD) is ~1.29 m, and the annual maximum active layer thickness (ALT) of permafrost is ~1.85 m. Temporally, ALT shows an overall increasing trend at an average rate of +3.17 cm yr−1, while SFD exhibits both decreasing (at ~62% areas) and increasing (at ~38% areas) trends in the region. Again, LST is found to be the dominant factor that controls the temporal changes in both SFD and ALT while precipitation (i.e., both rainfall and snowfall) plays an important (especially in more arid areas and regions near the lower limit of permafrost) but secondary role. Our results demonstrate the advantages of the satellite-based method in frozen soil simulations over large scales with complex topography and landscape and highlight the important roles of both temperature and precipitation in shaping the frozen soil patterns on the TP or other cold, dry regions.

Changing climate and the permafrost environment on the Qinghai–Tibet (Xizang) plateau

AbstractPermafrost on the Qinghai–Tibet Plateau (QTP) has undergone degradation as a result of recent climate change. This may alter the thermo‐hydrological processes and unlock soil organic carbon, and thereby affect local hydrological, ecological, and climatic systems. The relationships between permafrost and climate change have received extensive attention, and in this paper we review climate change for permafrost regions of the QTP over the past 30 years. We summarize the current state and changes in permafrost distribution and thickness, ground temperature, and ground ice conditions. We focus on changes in permafrost thermal state and in active‐layer thickness (ALT). Possible future changes in ground temperature and ALT are also discussed. Finally, we discuss the changes in hydrological processes and to ecosystems caused by permafrost degradation. Air temperature and ground temperature in the permafrost regions of the QTP have increased from 1980 to 2018, and the active layer has been thickening at a rate of 19.5 cm per decade. The response of permafrost to climate change is not as fast as in some reports, and permafrost degradation is slower than projected by models that do not account for conditions deep in permafrost.

Experimental observations that simulated active‐layer deepening drives deeper rock fracture

AbstractThe impact of changes in active‐layer thickness on the depth of pervasive macrofracturing (brecciation) in frost‐susceptible bedrock is unclear but important to understanding its physical properties and geohazard potential. Here we report results from a laboratory experiment to test the hypothesis that active‐layer deepening drives an increase in the depth of brecciation. The experiment simulated active‐layer deepening in 300 mm cubic blocks of limestone (chalk) and sandstone. Temperature, surface heave and strain at depth were measured during 16 freeze–thaw cycles. Macrocracks photographed at intervals were digitally analyzed to visualize crack growth and to quantify crack inclination and length. In chalk, an upper horizon of macrocracks developed first at about 100 mm depth in a shallow active layer during cycles 1–8, followed by a lower horizon at about 175–225 mm depth in a deeper active layer during cycles 9–16. The longest cracks (&gt;35 mm) were most common at inclinations of 0–30° from the horizontal, and numerous cracks &lt;5 to 15 mm long developed at inclinations of 40–50°, with some longer vertical to subvertical cracks linking the two brecciated horizons. Overall, the observations support the hypothesis that a thickening active layer drives deeper rock fracture by ice segregation.

Dynamical Gaseous Rings in Global Simulations of Protoplanetary Disk Formation

Abstract Global numerical simulations of protoplanetary disk formation and evolution were conducted in the thin-disk limit, where the model included a magnetically layered disk structure, a self-consistent treatment for the infall from cloud core, and the smallest possible inner computational boundary. We compared the evolution of a layered disk with a fully magnetically active disk. We also studied how the evolution depends on the parameters of the layered disk model—the MRI triggering temperature and active layer thickness—as well as the mass of the prestellar cloud core. With the canonical values of parameters a dead zone formed within the inner ≈15 au region of the magnetically layered disk. The dead zone was not a uniform structure, and long-lived, axisymmetric, gaseous rings ubiquitously formed within this region owing to the action of viscous torques. The rings showed a remarkable contrast in the disk environment as compared to a fully magnetically active disk and were characterized by high surface density and low effective viscosity. Multiple gaseous rings could form simultaneously in the dead zone region, which were highly dynamical and showed complex, time-dependent behavior such as inward migration, vortices, gravitational instability, and large-scale spiral waves. An increase in MRI triggering temperature had only marginal effects, while changes in active layer thickness and the initial cloud core mass had significant effects on the structure and evolution of the inner disk. Dust with large fragmentation barrier could be trapped in the rings, which may play a key role in planet formation.

Projected Changes in Permafrost Active Layer Thickness Over the Qinghai‐Tibet Plateau Under Climate Change

AbstractClimate warming would increase the active layer thickness (ALT) of permafrost, which can cause changes in the hydrological cycle, ecological processes, and carbon flux in cold regions. However, changes in permafrost ALT due to climate warming remain poorly quantified, which limits our understanding of environmental change in cold regions. In this study, the Lund‐Postam‐Jena dynamic vegetation model is coupled to the Kudryavtsev model to examine changes in permafrost ALT on the Qinghai‐Tibet Plateau (QTP) under climate change scenarios based on the representative concentration pathways (RCPs). The results suggest that the permafrost ALT on the QTP would exhibit a significant increasing trend under the climate change scenarios, and a large increment of ALT may occur in the northwestern QTP. In the near‐term (2011–2040), the change in ALT on the QTP is different under the RCP2.6, RCP4.5, RCP6.0, and RCP8.5 emissions scenarios, with an increment of 5–30 cm. In the mid‐term (2041–2070), ALT would deepen further with an obvious reduction in permafrost area, while the increase in ALT decreases from south to north. In the long‐term (2071–2099), the average increment of ALT would be greater than 30 cm under the RCP4.5, RCP6.0, and RCP8.5 scenarios, and the increment in ALT increases from south to north, with a remarkable retreat in permafrost area from south to north.

Diagnosis of the hydrology of a small Arctic permafrost catchment using HBV conceptual rainfall-runoff model

Abstract Changes in active layer thickness (ALT) over Arctic and permafrost regions have an important impact on rainfall-runoff transformation. General warming is observed across Svalbard Archipelago and corresponds to increases in ground temperatures. Permafrost thaw and changes in ALT due to climate warming alter how water is routed and stored in catchments, and thus impact both surface and subsurface processes. The overall aim of the present study is to examine the relationships between temporal changes of active layer depth and hydrological model parameters, together with variation in the catchment response. The analysis was carried out for the small unglaciated catchment Fuglebekken, located in the vicinity of the Polish Polar Station Hornsund on Spitsbergen. For hydrological modelling, the conceptual rainfall-runoff HBV (Hydrologiska Byråns Vattenbalansavdelning) model was used. The model was calibrated and validated on runoff within subperiods. A moving window approach (3 weeks long) was applied to derive temporal variation of parameters. Model calibration, together with an estimation of parametric uncertainty, was carried out using the Shuffled Complex Evolution Metropolis algorithm. This allowed the dependence of HBV model parameters on ALT to be analysed. Also, we tested the influence of model simplification, correction of precipitation, and initial conditions on the modelling results.

Modeling Wildfire-Induced Permafrost Deformation in an Alaskan Boreal Forest Using InSAR Observations

The discontinuous permafrost zone is one of the world’s most sensitive areas to climate change. Alaskan boreal forest is underlain by discontinuous permafrost, and wildfires are one of the most influential agents negatively impacting the condition of permafrost in the arctic region. Using interferometric synthetic aperture radar (InSAR) of Advanced Land Observation Satellite (ALOS) Phased Array type L-band Synthetic Aperture Radar (PALSAR) images, we mapped extensive permafrost degradation over interior Alaskan boreal forest in Yukon Flats, induced by the 2009 Big Creek wildfire. Our analyses showed that fire-induced permafrost degradation in the second post-fire thawing season contributed up to 20 cm of ground surface subsidence. We generated post-fire deformation time series and introduced a model that exploited the deformation time series to estimate fire-induced permafrost degradation and changes in active layer thickness. The model showed a wildfire-induced increase of up to 80 cm in active layer thickness in the second post-fire year due to pore-ice permafrost thawing. The model also showed up to 15 cm of permafrost degradation due to excess-ice thawing with little or no increase in active layer thickness. The uncertainties of the estimated change in active layer thickness and the thickness of thawed excess ice permafrost are 27.77 and 1.50 cm, respectively. Our results demonstrate that InSAR-derived deformation measurements along with physics models are capable of quantifying fire-induced permafrost degradation in Alaskan boreal forests underlain by discontinuous permafrost. Our results also have illustrated that fire-induced increase of active layer thickness and excess ice thawing contributed to ground surface subsidence.

Spatiotemporal Changes in Active Layer Thickness under Contemporary and Projected Climate in the Northern Hemisphere

Abstract Variability of active layer thickness (ALT) in permafrost regions is critical for assessments of climate change, water resources, and engineering applications. Detailed knowledge of ALT variations is also important for studies on ecosystem, hydrological, and geomorphological processes in cold regions. The primary objective of this study is therefore to provide a comprehensive 1971–2000 climatology of ALT and its changes across the entire Northern Hemisphere from 1850 through 2100. To accomplish this, in situ observations, the Stefan solution based on a thawing index, and the edaphic factor (E factor) are employed to calculate ALT. The thawing index is derived from (i) the multimodel ensemble mean of 16 models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) over 1850–2005, (ii) three representative concentration pathways (RCP2.6, RCP4.5, and RCP8.5) for 2006–2100, and (iii) Climatic Research Unit (CRU) gridded observations for 1901–2014. The results show significant spatial variability in in situ ALT that generally ranges from 40 to 320 cm, with some extreme values of 900 cm in the Alps. The differences in the ALT climatology between the three RCPs and the historical experiments ranged from 0 to 200 cm. The biggest increases, of 120–200 cm, are on the Qinghai–Tibetan Plateau, while the smallest increases of less than 20 cm are in Alaska. Averaged over all permafrost regions, mean ALT from CMIP5 increased significantly at 0.57 ± 0.04 cm decade−1 during 1850–2005, while 2006–2100 projections show ALT increases of 0.77 ± 0.08 cm decade−1 for RCP2.6, 2.56 ± 0.07 cm decade−1 for RCP4.5, and 6.51 ± 0.07 cm decade−1 for RCP8.5.