Monitoring and modelling the evolution of ice-rich peat plateaus and palsas in Northern Norway

Peat plateaus are permafrost bearing morphologies distributed in the discontinuous permafrost zone, at the margin of permafrost areas. It is a warm type of permafrost, particularly sensitive to climate changes. In Northern Norway, peat plateaus have been degrading over the last 60 years (Borge et al., 2016), giving the opportunity for process studies that can shed light on the future of vast permafrost peatlands such as in Western Siberia. The large scale temperature signal that drives permafrost dynamics on the long run is largely modulated by local factors on the decadal time scale, such as the micro-topography that affects the snow distribution and the soil water balance. These local parameters create a high spatial variability of the ground surface temperatures, and, within a few meters, conditions can evolve from permafrost stability to permafrost incompatibility. We present a permafrost modelling work that is coupled to a monitoring data set of peat plateaus in Northern Norway. We use this dataset to identify key variables and processes driving the ground surface temperature and to benchmark the CryoGrid3 permafrost model (Westermann et al., 2016). The forcing data are derived from meso-scale atmospheric modelling (Aas et al. 2015).

We investigate the impact of the winter and summer hydrology (snow distribution, precipitation and surface/subsurface water flow). We show how these parameters can locally create favorable conditions for permafrost stability. Based on a steady state sensitivity test, we confirm the crucial effect of the snow cover than can affect the 1 m deep Mean Annual Ground Temperature (1m-MAGT) by more than 3°C. Soil moisture is also critical, with a temperature offset reaching 2°C on the 1m-MAGT between drained and saturated conditions.

In a second time, a new version of the model performing coupled realization is used to reproduce the lateral erosion of the peat plateau we observe on drone imagery. This version includes lateral fluxes of heat, snow and water between the realizations and account for the excess ice melt. This modelling work provides new insights on the timing of the expected degradation of the peat plateaus. It also gives the opportunity to investigate the feedback between the modification of the micro-topography, the temperature profile evolution and the lateral fluxes.