Hydrologic-land surface modelling of the Canadian sporadic-discontinuous
permafrost: initialization and uncertainty propagation
Permafrost thaw has been observed in recent decades in the Northern
Hemisphere and is expected to accelerate with continued global warming.
Predicting the future of permafrost requires proper representation of
the interrelated surface/subsurface thermal and hydrologic regimes. Land
surface models (LSMs) are well suited for such predictions, as they
couple heat and water interactions across soil-vegetation-atmosphere
interfaces and can be applied over large scales. LSMs, however, are
challenged by the long-term thermal and hydraulic memories of permafrost
and the paucity of historical records to represent permafrost dynamics
under transient climate conditions. In this study, we address the
challenge of model initialization by characterizing the impact of
initial climate conditions and initial soil frozen and liquid water
contents on the simulation length required to reach equilibrium.
Further, we quantify how the uncertainty in model initialization
propagates to simulated permafrost dynamics. Modelling experiments are
conducted with the Modélisation Environmentale Communautaire – Surface
and Hydrology (MESH) framework and its embedded Canadian Land Surface
Scheme (CLASS). The study area is in the Liard River basin in the
Northwest Territories of Canada with sporadic and discontinuous regions.
Results show that uncertainty in model initialization controls various
attributes of simulated permafrost, especially the active layer
thickness, which could change by 0.5-1.5m depending on the initial
condition chosen. The least number of spin-up cycles is achieved with
near field capacity condition, but the number of cycles varies depending
on the spin-up year climate. We advise an extended spin-up of 200-1000
cycles to ensure proper model initialization under different climatic
conditions and initial soil moisture contents.