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.