Transient Modeling of Permafrost Distribution From 1986 to 2016 in Mongolia

The distribution of permafrost in the southernmost zones is complicated in both time and space. We assessed this complexity by applying transient heat transfer schemes to model permafrost in Mongolia between 1986 and 2016. The modeling took into account the spatial distribution of soil thermal properties and time series of ground temperature profiles observed at 69 borehole sites. Spatial modeling was forced by downscaled ERA5 air temperatures that were further debiased with local meteorological records. The results indicated that permafrost warmed by 0°C to 0.4°C/decade, most significantly in eastern and northern Hangai and at high elevations in the Altai Mountains. The extent of permafrost remained stable, but the active layer was thickened, especially after the late 1990s. Forested wet soils experienced less warming, while temperatures in soils with low organic matter and low moisture content increased by 0.5°C over the modeling period. The lower limits of mountain permafrost were estimated to be between 1320 and 2030 m a.s.l., depending on the latitude. Our permafrost map allows the delineation of a complex distribution of permafrost in Mongolia, which is strongly controlled by the spatially complex topography, landcovers, and soil wetness.