Articles | Volume 12, issue 1
The Cryosphere, 12, 145–161, 2018
The Cryosphere, 12, 145–161, 2018

Research article 16 Jan 2018

Research article | 16 Jan 2018

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

Yonghong Yi1, John S. Kimball1, Richard H. Chen2, Mahta Moghaddam2, Rolf H. Reichle3, Umakant Mishra4, Donatella Zona5, and Walter C. Oechel5 Yonghong Yi et al.
  • 1Numerical Terradynamic Simulation Group, The University of Montana, Missoula MT, USA
  • 2Department of Electrical Engineering, University of Southern California, CA, USA
  • 3Global Modeling and Assimilation Office, NASA Goddard Space Flight Center, Greenbelt, MD, USA
  • 4Environmental Science Division, Argonne National Laboratory, Argonne, IL, USA
  • 5Department of Biology, San Diego State University, San Diego, CA, USA

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.

Short summary
An important feature of the Arctic is large spatial heterogeneity in active layer conditions. We developed a modeling framework integrating airborne longwave radar and satellite data to investigate active layer thickness (ALT) sensitivity to landscape heterogeneity in Alaska. We find uncertainty in spatial and vertical distribution of soil organic carbon is the largest factor affecting ALT accuracy. Advances in remote sensing of soil conditions will enable more accurate ALT predictions.