Comparison of model-produced active layer fields: Results for northern Alaska

In this study we compare gridded active layer thickness (ALT) fields representing northern Alaska produced by the State Hydrological Institute (SHI), National Snow and Ice Data Center (NSIDC), and Geophysical Institute–University of Alaska Fairbanks (UAF-GIPL 2.0) spatial permafrost models. Comparison of model-produced ALT fields representing northern Alaska revealed substantial differences. The largest difference in modeled ALT was found in the interior of Alaska. However, the spatial distribution of observational sites, most of which are on the North Slope, precludes definitive conclusions about the accuracy of model prediction for the Alaskan interior. Accuracy of the model-produced ALT fields was assessed at a series of monitoring sites and over a 27,000 km2 region in north-central Alaska with known spatial ALT distribution. The NSIDC model is very accurate over the extent of the topographically homogeneous Coastal Plain but overestimates ALT in more complex terrain of the Brooks Range Foothills. The UAF-GIPL 2.0 model reproduced site-specific active layer values well but overestimated ALT on the Coastal Plain. Although the SHI model provided relatively accurate estimates, it was unable to reproduce interannual active layer dynamics. Large differences in ALT fields have primarily resulted from differences in approaches adopted in each model for characterization of largely unknown spatial distribution of surface (vegetation, snow) and subsurface (soil properties, soil moisture) conditions. Results from this study identify the nature and magnitude of error in ALT fields produced by permafrost models.