scholarly journals Characterizing permafrost soil active layer dynamics and sensitivity to landscape spatial heterogeneity in Alaska

2017 ◽  
Author(s):  
Yonghong Yi ◽  
John S. Kimball ◽  
Richard Chen ◽  
Mahta Moghaddam ◽  
Rolf H. Reichle ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Spatial Heterogeneity ◽  
Active Layer ◽  
Landscape Heterogeneity ◽  
The Arctic ◽  
Integrated Modelling ◽  
Permafrost Soil ◽  
Soil Conditions ◽  
Active Layer Thickness ◽  
Recent Climate

Abstract. An important feature of the Arctic is large spatial heterogeneity in active layer conditions, which is generally poorly represented by global models. In this study, we developed a spatially integrated modelling and analysis framework combining field observations, local scale (~ 50 m) active layer thickness (ALT) and soil moisture maps derived from airborne low frequency (L + P-band) radar measurements, and global satellite environmental observations to investigate the ALT sensitivity to recent climate trends and landscape heterogeneity in Alaska. Model simulated ALT results show good correspondence with in-situ measurements in higher permafrost probability (PP ≥ 70 %) areas (n = 33, R = 0.60, mean bias = 1.58 cm, RMSE = 20.32 cm). The model results also reveal widespread ALT deepening since 2001, with smaller ALT increases in northern Alaska (mean trend = 0.32 ± 1.18 cm yr-1) and much larger increases (> 3 cm yr-1) across interior and southern Alaska. The positive ALT trend coincides with regional warming and a longer snow-free season (R = 0.60 ± 0.32). Uncertainty in the spatial and vertical distribution of soil organic carbon (SOC) was found to be the most important factor affecting model ALT accuracy. Potential improvements in characterizing SOC heterogeneity, including better spatial sampling of soil conditions and advances in remote sensing of SOC and soil moisture, will enable more accurate predictions of permafrost active layer conditions.

scholarly journals Characterizing permafrost active layer dynamics and sensitivity to landscape spatial heterogeneity in Alaska

2018 ◽  
Vol 12 (1) ◽  
pp. 145-161 ◽  
Author(s):  
Yonghong Yi ◽  
John S. Kimball ◽  
Richard H. Chen ◽  
Mahta Moghaddam ◽  
Rolf H. Reichle ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Spatial Heterogeneity ◽  
Active Layer ◽  
The Arctic ◽  
Soil Conditions ◽  
Integrated Analysis ◽  
Active Layer Thickness ◽  
Modeling Framework ◽  
Discontinuous Permafrost ◽  
Recent Climate

Abstract. An important feature of the Arctic is large spatial heterogeneity in active layer conditions, which is generally poorly represented by global models and can lead to large uncertainties in predicting regional ecosystem responses and climate feedbacks. In this study, we developed a spatially integrated modeling and analysis framework combining field observations, local-scale ( ∼  50 m resolution) active layer thickness (ALT) and soil moisture maps derived from low-frequency (L + P-band) airborne radar measurements, and global satellite environmental observations to investigate the ALT sensitivity to recent climate trends and landscape heterogeneity in Alaska. Modeled ALT results show good correspondence with in situ measurements in higher-permafrost-probability (PP  ≥  70 %) areas (n = 33; R = 0.60; mean bias  =  1.58 cm; RMSE  =  20.32 cm), but with larger uncertainty in sporadic and discontinuous permafrost areas. The model results also reveal widespread ALT deepening since 2001, with smaller ALT increases in northern Alaska (mean trend  = 0.32±1.18 cm yr−1) and much larger increases (>  3 cm yr−1) across interior and southern Alaska. The positive ALT trend coincides with regional warming and a longer snow-free season (R =  0.60 ± 0.32). A spatially integrated analysis of the radar retrievals and model sensitivity simulations demonstrated that uncertainty in the spatial and vertical distribution of soil organic carbon (SOC) was the largest factor affecting modeled ALT accuracy, while soil moisture played a secondary role. Potential improvements in characterizing SOC heterogeneity, including better spatial sampling of soil conditions and advances in remote sensing of SOC and soil moisture, will enable more accurate predictions of active layer conditions and refinement of the modeling framework across a larger domain.

scholarly journals The influence of climate and hydrological variables on opposite anomaly in active layer thickness between Eurasian and North American watersheds

2012 ◽  
Vol 6 (4) ◽  
pp. 2537-2574 ◽  
Author(s):  
H. Park ◽  
J. Walsh ◽  
A. N. Fedorov ◽  
A. B. Sherstiukov ◽  
Y. Iijima ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Layer Thickness ◽  
Active Layer ◽  
Air Temperature ◽  
North American ◽  
Snow Depth ◽  
The Arctic ◽  
Surface Model ◽  
Active Layer Thickness ◽  
Hydrological Variables

Abstract. This study not only examined the spatiotemporal variations of permafrost active layer thickness (ALT) during 1948–2006 over the terrestrial Arctic regions experiencing climate changes, but also identified the associated drivers based on observational data and a simulation conducted by a land surface model (CHANGE). The focus on the ALT extends previous studies that have emphasized ground temperatures in permafrost regions. The Ob, Yenisey, Lena, Yukon, and Mackenzie watersheds are foci of the study. Time series of ALT in Eurasian watersheds showed generally increasing trends, while ALT in North American watersheds showed decreases. An opposition of ALT variations implicated with climate and hydrological variables was most significant when the Arctic air temperature entered into a warming phase. The warming temperatures were not simply expressed to increases in ALT. Since 1990 when the warming increased, the forcing of the ALT by the higher Annual Thawing Index in the Mackenzie and Yukon Basins was offset by the combined effects of less insulation caused by thinner snow depth and drier soil during summer. In contrast, the increasing Annual Thawing Index together with thicker snow depth and higher summer soil moisture in the Lena contributed to the increase in ALT. The results imply that the soil thermal and moisture regimes formed in the pre-thaw season(s) provide memory that manifests itself during the summer. While it is widely believed that ALT will increase with global warming, this hypothesis may need modification because the ALT also shows responses to variations in snow depth and soil moisture that can over-ride the effect of air temperature. The dependence of the hydrological variables driven by the atmosphere further increases the uncertainty in future changes of the permafrost active layer.

scholarly journals The influence of climate and hydrological variables on opposite anomaly in active-layer thickness between Eurasian and North American watersheds

2013 ◽  
Vol 7 (2) ◽  
pp. 631-645 ◽  
Author(s):  
H. Park ◽  
J. Walsh ◽  
A. N. Fedorov ◽  
A. B. Sherstiukov ◽  
Y. Iijima ◽  
...  
Keyword(s):  
Layer Thickness ◽  
Active Layer ◽  
North American ◽  
Land Surface ◽  
Snow Depth ◽  
The Arctic ◽  
Surface Model ◽  
Active Layer Thickness ◽  
Hydrological Variables ◽  
Permafrost Regions

Abstract. This study not only examined the spatiotemporal variations of active-layer thickness (ALT) in permafrost regions during 1948–2006 over the terrestrial Arctic regions experiencing climate changes, but also identified the associated drivers based on observational data and a simulation conducted by a land surface model (CHANGE). The focus on the ALT extends previous studies that have emphasized ground temperatures in permafrost regions. The Ob, Yenisey, Lena, Yukon, and Mackenzie watersheds are foci of the study. Time series of ALT in Eurasian watersheds showed generally increasing trends, while the increase in ALT in North American watersheds was not significant. However, ALT in the North American watersheds has been negatively anomalous since 1990 when the Arctic air temperature entered into a warming phase. The warming temperatures were not simply expressed to increases in ALT. Since 1990 when the warming increased, the forcing of the ALT by the higher annual thawing index (ATI) in the Mackenzie and Yukon basins has been offset by the combined effects of less insulation caused by thinner snow depth and drier soil during summer. In contrast, the increasing ATI together with thicker snow depth and higher summer soil moisture in the Lena contributed to the increase in ALT. The results imply that the soil thermal and moisture regimes formed in the pre-thaw season(s) provide memory that manifests itself during the summer. The different ALT anomalies between Eurasian and North American watersheds highlight increased importance of the variability of hydrological variables.

scholarly journals An improved representation of physical permafrost dynamics in the JULES land surface model

2015 ◽  
Vol 8 (1) ◽  
pp. 715-759 ◽  
Author(s):  
S. Chadburn ◽  
E. Burke ◽  
R. Essery ◽  
J. Boike ◽  
M. Langer ◽  
...  
Keyword(s):  
Organic Matter ◽  
Soil Moisture ◽  
Active Layer ◽  
Land Surface ◽  
Climate Models ◽  
Surface Soil ◽  
Active Layer Thickness ◽  
Mean Square ◽  
Near Surface ◽  
Soil Temperatures

Abstract. It is important to correctly simulate permafrost in global climate models, since the stored carbon represents the source of a potentially important climate feedback. This carbon feedback depends on the physical state of the permafrost. We have therefore included improved physical permafrost processes in JULES, which is the land-surface scheme used in the Hadley Centre climate models. The thermal and hydraulic properties of the soil were modified to account for the presence of organic matter, and the insulating effects of a surface layer of moss were added, allowing for fractional moss cover. We also simulate a higher-resolution soil column and deeper soil, and include an additional thermal column at the base of the soil to represent bedrock. In addition, the snow scheme was improved to allow it to run with arbitrarily thin layers. Point-site simulations at Samoylov Island, Siberia, show that the model is now able to simulate soil temperatures and thaw depth much closer to the observations. The root mean square error for the near-surface soil temperatures reduces by approximately 30%, and the active layer thickness is reduced from being over 1 m too deep to within 0.1 m of the observed active layer thickness. All of the model improvements contribute to improving the simulations, with organic matter having the single greatest impact. A new method is used to estimate active layer depth more accurately using the fraction of unfrozen water. Soil hydrology and snow are investigated further by holding the soil moisture fixed and adjusting the parameters to make the soil moisture and snow density match better with observations. The root mean square error in near-surface soil temperatures is reduced by a further 20% as a result.

scholarly journals Nonlinear thermal and moisture dynamics of high Arctic wetland polygons following permafrost disturbance

2015 ◽  
Vol 12 (14) ◽  
pp. 11797-11831 ◽  
Author(s):  
E. Godin ◽  
D. Fortier ◽  
E. Lévesque
Keyword(s):  
Active Layer ◽  
Arid Region ◽  
High Arctic ◽  
Permafrost Soil ◽  
Active Layer Thickness ◽  
Green House Gas ◽  
Heterogeneous Nature ◽  
Thaw Depth ◽  
Moisture Dynamics ◽  
Permafrost Regions

Abstract. Low-centre polygonal terrain developing within gentle sloping surfaces and lowlands in the high Arctic have a potential to retain snowmelt water in their bowl-shaped centre and as such are considered high latitude wetlands. Such wetlands in the continuous permafrost regions have an important ecological role in an otherwise generally arid region. In the valley of the glacier C-79 on Bylot Island (Nunavut, Canada), thermal erosion gullies are rapidly eroding the permafrost along ice wedges affecting the integrity of the polygons by breaching and collapsing the surrounding rims. While intact polygons were characterized by a relative homogeneity (topography, snow cover, maximum active layer thaw depth, ground moisture content, vegetation cover), eroded polygons had a non-linear response for the same elements following their perturbation. The heterogeneous nature of disturbed terrains impacts active layer thickness, ground ice aggradation in the upper portion of permafrost, soil moisture and vegetation dynamics, carbon storage and terrestrial green-house gas emissions.

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

2016 ◽  
Author(s):  
C. Schuh ◽  
A. Frampton ◽  
H. H. Christiansen
Keyword(s):  
Soil Moisture ◽  
Layer Thickness ◽  
Active Layer ◽  
Field Data ◽  
Large Field ◽  
Thickness Variation ◽  
Unfrozen Water ◽  
Active Layer Thickness ◽  
Retention Characteristics ◽  
Moisture Redistribution

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 are 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 of ice distribution and circulation within the active layer by cryosuction 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, observed and modelled) including an increasing active layer thickness (0.8 cm/yr, observed and 0.3 to 0.8 cm/yr, modelled) during the 14-year study period.

Contrasting thermal responses of permafrost to winter warming events under different snow regimes in the subarctic

2021 ◽  
Author(s):  
Didac Pascual Descarrega ◽  
Margareta Johansson
Keyword(s):  
Layer Thickness ◽  
Active Layer ◽  
Snow Depth ◽  
Thermal Response ◽  
Winter Precipitation ◽  
The Arctic ◽  
Active Layer Thickness ◽  
Thermal Dynamics ◽  
Winter Warming

<p>Winter warming events (WWE) in the Swedish subarctic are abrupt and short-lasting (hours-to-days) events of positive air temperature that occur during wintertime, sometimes accompanied by rainfall (rain on snow; ROS). These events cause changes in snow properties, which affect the below-ground thermal regime that, in turn, controls a suite of ecosystem processes ranging from microbial activity to permafrost and vegetation dynamics. For instance, winter melting can cause ground warming due to the shortening of the snow cover season, or ground cooling as the reduced snow depth and the formation of refrozen layers of high thermal conductivity at the base of the snowpack facilitate the release of soil heat. Apart from these interacting processes, the overall impacts of WWE on ground temperatures may also depend on the timing of the events and the preceding snowpack characteristics. The frequency and intensity of these events in the Arctic, including the Swedish subarctic, has increased remarkably during the recent decades, and is expected to increase even further during the 21st Century. In addition, snow depth (not necessarily snow duration) is projected to increase in many parts of the Arctic, including the Swedish subarctic. In 2005, a manipulation experiment was set up on a lowland permafrost mire in the Swedish subarctic, to simulate projected future increases in winter precipitation. In this study, we analyse this 15-year record of ground temperature, active layer thickness, and meteorological variables, to evaluate the short- (days to weeks) and long-term (up to 1 year) impacts of WWE on the thermal dynamics of lowland permafrost, and provide new insights into the influence of the timing of WWE and the underlying snowpack conditions on the thermal response of permafrost. On the short-term, the thermal responses to WWE are faster and stronger in areas with a shallow snowpack (5-10 cm), although these responses are more persistent in areas with a thicker snowpack (>25 cm), especially after ROS events. On the long term, permafrost in areas with a thicker snowpack exhibit a more durable warming response to WWE that results in thicker active layers at the end of the season. On the contrary, we do not observe a correlation between WWE and end of season active layer thickness in areas with a shallow snowpack. </p>

Permafrost Dynamics Observatory: Retrieval of Active Layer Thickness and Soil Moisture from Airborne Insar and Polsar Data

2021 ◽  
Author(s):  
Richard H. Chen ◽  
Roger J. Michaelides ◽  
Yuhuan Zhao ◽  
Lingcao Huang ◽  
Elizabeth Wig ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Layer Thickness ◽  
Active Layer ◽  
Active Layer Thickness

scholarly journals An improved representation of physical permafrost dynamics in the JULES land-surface model

2015 ◽  
Vol 8 (5) ◽  
pp. 1493-1508 ◽  
Author(s):  
S. Chadburn ◽  
E. Burke ◽  
R. Essery ◽  
J. Boike ◽  
M. Langer ◽  
...  
Keyword(s):  
Organic Matter ◽  
Soil Moisture ◽  
Active Layer ◽  
Land Surface ◽  
Climate Models ◽  
Surface Soil ◽  
Active Layer Thickness ◽  
Mean Square ◽  
Near Surface ◽  
Soil Temperatures

Abstract. It is important to correctly simulate permafrost in global climate models, since the stored carbon represents the source of a potentially important climate feedback. This carbon feedback depends on the physical state of the permafrost. We have therefore included improved physical permafrost processes in JULES (Joint UK Land Environment Simulator), which is the land-surface scheme used in the Hadley Centre climate models. The thermal and hydraulic properties of the soil were modified to account for the presence of organic matter, and the insulating effects of a surface layer of moss were added, allowing for fractional moss cover. These processes are particularly relevant in permafrost zones. We also simulate a higher-resolution soil column and deeper soil, and include an additional thermal column at the base of the soil to represent bedrock. In addition, the snow scheme was improved to allow it to run with arbitrarily thin layers. Point-site simulations at Samoylov Island, Siberia, show that the model is now able to simulate soil temperatures and thaw depth much closer to the observations. The root mean square error for the near-surface soil temperatures reduces by approximately 30%, and the active layer thickness is reduced from being over 1 m too deep to within 0.1 m of the observed active layer thickness. All of the model improvements contribute to improving the simulations, with organic matter having the single greatest impact. A new method is used to estimate active layer depth more accurately using the fraction of unfrozen water. Soil hydrology and snow are investigated further by holding the soil moisture fixed and adjusting the parameters to make the soil moisture and snow density match better with observations. The root mean square error in near-surface soil temperatures is reduced by a further 20% as a result.

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