Ninth International Conference on Permafrost ... - IARC Research

Modeling Thermal and Moisture Regimes of Permafrost with New Deep SoilConfiguration in CLASSJean-Philippe Blanchette, Laxmi Sushama, René LapriseCentre pour l’étude et la simulation à l’échelle régionale, Université du Québec à Montréal, Montréal, CanadaCanadian Regional Climate Modelling and Diagnostics Network, Montréal, CanadaConsortium Ouranos on Regional Climate and Adaptation to Climate Changes, Montréal CanadaIntroductionMost of the climate models, including Regional ClimateModels (RCMs), employ land-surface schemes that vary indepth between 3 and 10 m; for example, the current versionof the Canadian Regional Climate Model (CRCM) has aphysically-based land surface scheme, CLASS (CanadianLand Surface Scheme; Verseghy et al. 1991, Verseghy 1993),which is 4.1 m deep, with three soil layers that are 0.1, 0.25,and 3.75 m thick, respectively. As shown by many recentstudies (Smerdon & Stieglitz 2006, Alexeev et al. 2007,Nicolsky et al. 2007, Stevens et al. 2007), such shallow-soilmodels, though coupled, cannot simulate active-layer andnear-surface permafrost realistically. To simulate realisticsoil thermal and moisture regimes in the CRCM, it isFigure 1. Average ground heat flux for the 1980–1990 period, for6 (dash-multidotted line) and 10-layer (solid line) configurations,and their differences (dash-dotted line). The annual maximumdifference, the annual mean difference, and the standard deviationare also indicated in the Figures.intended to use the latest version (v. 3.3) of CLASS, whichis particularly suitable for permafrost studies due to its moreflexible layering scheme and bottom boundary conditions.Sensitivity of the soil thermal and moisture regimes to thesoil model depth/configuration is assessed using offlinesimulations with this latest version of CLASS, which ispresented in this paper.Experiments and Model ConfigurationThe offline simulations were performed with CLASS fora location in northern Québec with continuous permafrost,for the 1961–1999 period. The input variables (downwardvisible and infrared radiation, precipitation, atmosphericpressure, surface air temperature, specific humidity, andwind) required to drive the soil model were specified usingthe European Re-analysis datasets (ERA-40, Uppala et al.2005). The soil properties were specified using the landsurface datasets developed by Wilson and Henderson-Sellers (1985), according to which the bedrock is at 0.1 mbelow surface for the chosen location. Three experimentswere performed, with the lower boundary at 4.1, 40.2, and133.7 m below surface, respectively. The layer thicknessvaries exponentially from top to bottom (0.10, 0.17, 0.31,0.57, 1.04, and 1.91 m for the first six layers and so on),and accordingly the number of layers for the three cases is6, 10, and 12, respectively. The initial profile is determinedby iteratively running the soil model from chosen conditionsusing 1961 data, until equilibrium is reached.ResultsPreliminary results confirm that adding deeper layers toCLASS, and in doing so, lowering the bottom boundary withzero soil heat conduction flux, changes the thermal regime, asshown in Figures 1, 2, and 3, comparing the six and ten-layerconfiguration. The thermal inertia brought by new deeperFigure 2. Average temperature differences between the 10- and 6-layer configuration for the 1995–1999 period.23