Inferring Permafrost Active Layer Thermal Properties From Numerical Model Optimization

Permafrost has become increasingly unstable as a result of surface warming; therefore it is crucial to improve our understanding of permafrost spatiotemporal dynamics to assess the impact of active layer thickening on future hydrogeological processes. However, direct determinations of permafrost active-layer thermal properties are few, resulting in large uncertainty in forecasts of active layer thickness. To assess how to reduce the uncertainty without expanding monitoring efforts, a total of 1,728 numerical 1D models were compared using three error measures against observed active layer temperature data from the Qinghai-Tibetan Plateau. Resulting optimized parameter values varied depending on the error measure used, but agree with reported ones: bulk volumetric heat capacity is 1.82-1.94 x106Jm3 K, bulk thermal conductivity 1.0-1.2 W/m K and porosity 0.25-0.45 (-). The active layer thickening rate varied significantly for the three error measures, as demonstrated by a similar to 15 years thawing time-lag between the error measures over a 100 years modeling period.

Automated summary

Comparison of numerical models with observed data revealed ranges of thermal properties in the active layer and significant differences in thickening rates under different error measures.