Abstract
This study investigates the sensitivity of the Canadian Regional Climate Model (CRCM5) simulated near surface permafrost and its climate interactions to soil and snow formulations. In particular, sensitivities to the depth of the soil column, inclusion of organic soils and modified snow conductivity formulation are investigated. The impact of these modifications are first assessed in offline simulations performed with the Canadian Land Surface Scheme (CLASS), which is the land surface scheme used in CRCM5, when driven by ERA-40/ERA-Interim for the 1957–2008 period. Analysis of CLASS simulations shows major improvements in the simulated permafrost extent, particularly with a deeper soil column. Inclusion of organic soil decreased the summer ground heat flux and therefore the summer soil temperatures, leading to improvements in the simulated active layer thickness (ALT). The impact of the new snow thermal conductivity formulation is moderate compared to the effect of organic soils, but reduces the cold biases in winter soil temperatures. CRCM5 experiments revealed similar sensitivities to soil depth, organic soil and snow conductivity changes as with the offline simulations. Significant changes are noted in the land–atmosphere interactions, through modified energy and moisture partitioning at the surface resulting from the inclusion of the organic soils. The inter-annual variability of the ALT shows larger sensitivities to summer temperatures for mineral soil while experiments including organic soils show increased sensitivities to annual temperatures. The ALT trends in the CRCM5 are similar to the observed values, despite the overestimation of ALT associated with a warm bias in the CRCM5 climate.
Highlights
Permafrost covers approximately one quarter of all the exposed land of the continental northern hemisphere (Zhang et al 1999)
This study investigates the sensitivity of the Canadian Regional Climate Model (CRCM5) simulated near surface permafrost and its climate interactions to soil and snow formulations
The CRCM5 experiments are between CRU3.1 and UDel estimates, showing that CRCM5 is within the observational uncertainties but tends to be biased warm, in good agreement with the simulated biases noted over Eastern Siberia and North America (Fig. 8)
Summary
Permafrost covers approximately one quarter of all the exposed land of the continental northern hemisphere (Zhang et al 1999). Since the majority of the microbial decomposition occurs in the seasonally thawed active layer, increases in the ALT and permafrost thaw will increase decomposition of the soil organic matter, resulting in the release of carbon dioxide and/or methane to the atmosphere, depending on the type of decomposition, i.e. aerobic or anaerobic. This release of greenhouse gases, associated with permafrost thaw, will act as a positive feedback to climate warming (Zimov et al 2006) estimated between 2.8 and 7.8 °C by the end of the century
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