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Predicting Active-Layer Thicknesses of Permafrost-Affected Soils

Paper Reviewed
Mishra, U. and Riley, W.J. 2014. Active-layer thickness across Alaska: Comparing observation-based estimates with CMIP5 earth system model predictions. Soil Science Society of America Journal 78: 894-902.

In introducing their work, Mishra and Riley (2014) write that "predicted active-layer (AL) thicknesses of permafrost-affected soils influence Earth system model predictions of carbon-climate feedbacks," yet they say "only a few observation-based studies have estimated AL thicknesses across large regions and at the spatial scale at which they vary." Consequently, they went on to use spatially-referenced soil profile description data and environmental variables (topography, climate and land cover) in a geographically-weighted regression approach designed to predict the spatial variability of AL thicknesses across Alaska at a 60-meter spatial resolution.

This work of the two researchers revealed that "mean annual surface air temperature, land cover type, and slope gradient were primary controllers of AL thickness spatial variability." But when they compared their results with those that employed climate output obtained from Coupled Model Intercomparison Project Phase 5 (CMIP5) predictions, they found there were "large interquartile ranges in predicted AL thicknesses (0.35-4.4 m), indicating substantial overestimate of current AL thickness in Alaska, which might result in higher positive permafrost carbon feedback under future warming scenarios." And they further note, in this regard, that "the CMIP5 predictions of AL thickness spatial heterogeneity were unrealistic when compared with observations," adding that the prediction errors were several times larger compared to errors associated with their observation-based approach.

As for what this all means, the two scientists say their results indicate a "need for better process representations and representation of natural spatial heterogeneity due to local environment (topography, vegetation and soil properties) in Earth system models to generate a realistic variation of regional scale AL thickness, which could reduce the existing uncertainty in predicting permafrost carbon-climate feedbacks."

Posted 13 January 2015