Modeling of permafrost dynamics at two different biophysical settings near Dry Creek, Interior Alaska

The mean annual air temperature (MAAT) and winter snow cover are the two most important climate factors that bring changes to the thermal state of permafrost and active-layer at various temporal scales. However, the complex interaction among surface biophysical factors (such as topography, surface organic layer, soil texture, soil moisture, volume of ground ice and snow) manipulates the response of permafrost to climatic changes. To evaluate the effects of recent (1941-2008) climate change (i.e. change in air temperature and winter snow depth) on permafrost dynamics (particularly temperature) we reconstructed the thermal history of permafrost at two different biophysical settings using Geophysical Institute Permafrost Laboratory (GIPL) 2.0 numerical model. The modeling results suggest significant difference in response of permafrost to climate change at these two sites even though they experience similar climatic condition. The study found that permafrost temperature (at 1 m depth) rose by 0.6 °C and 1.0 °C and active-layer deepen to a maximum depth of 0.5 m and 1.0 m during 1976-1995 at the two sites in response to increase in MAAT, winter air temperature and snow depth. During 1996-2008 the permafrost temperature decreased by 0.5 °C at both the sites mainly due to record low winter snow depth. We found that snow has a much stronger influence on permafrost temperature and active-layer depth than previously understood. Further, the modeling results demonstrated that active-layer is not only a function of summer air temperature but also MAAT, winter air temperature and snow depth. The difference in the permafrost response between these two sites is due to the difference in the volume of ground ice. Permafrost at the site with more ground ice is more resilient to climate change.