The Canadian Land Surface Scheme (CLASS)

The Canadian Land Surface Scheme (CLASS) was initiated in 1987 to produce a ‘second generation’ land surface scheme for inclusion in the Canadian GCM (CanGCM) and has been under continual development since. The first publications describing CLASS were by Verseghy (1991)1 for the soil and snow algorithms and Verseghy (1993)2 for the vegetation algorithms. Development of CLASS has been predominantly within Environment Canada (later renamed Environment and Climate Change Canada; ECCC) with the exception of an organized community effort as part of the Canadian Climate Research Network (1994 – 1997; Verseghy, 2000)3 as well as ad-hoc collaborations with the broader research community. The final version of CLASS prior to incorporation in CLASSIC is version 3.6.24. As a land surface scheme, CLASS simulates the fluxes of energy, momentum, and water between the atmosphere and land surface.

General overview of processes simulated by CLASS

Evaluation of the performance of CLASS over the course of the model’s development has been extensive with numerous publications directly applying or evaluating the model. CLASS has been applied in an offline context (forced with observed meteorology; e.g., Bailey et al. (2000)5, Kothavala et al. (2005)6, Roy et al. (2013)7, Bartlett et al. (2006)8, Brown et al. (2006)9, Wu et al. (2016)10, Verseghy and MacKay (2017)11, Melton et al. 201912), as part of a regional climate model, e.g. CRCM (Ganji et al., 201513; Paquin and Sushama, 201414) and CanRCM (Scinocca et al., 2016)15, and integrated into each version of the Canadian Atmospheric Model (CanAM), Coupled Global Climate Model (CanCM), and Earth System Model (CanESM) since the early 1990s.

CLASS operates on a varying time-step between 15 and 30 minutes. This is typically set to 15 minutes when coupled to an atmosphere model and 30 minutes when forced with observed meteorology. CLASS uses vegetation characteristics (rooting depth, canopy mass, leaf area index (LAI), and vegetation height) for calculating the transfers of energy and momentum with the atmosphere. The number of soil layers can vary depending on application but the standard model setup uses twenty soil layers ranging from 10 layers of 0.1 m thickness gradually increasing to a 30 m thick layer for a total ground depth of over 61 m. CLASS prognostically determines the water content (liquid and frozen) and temperature of all soil layers each timestep. Water fluxes are calculated for ground layers within the permeable soil depth of the ground column, but not the underlying bedrock layers, whereas layer temperatures are calculated in both soil and bedrock layers. Also calculated each timestep are the temperature, mass, albedo, and density of the single layer snow pack (where it exists), the temperature and interception and storage of rain and snow on the vegetation canopy, and the temperature and depth of ponded water on the soil surface. Each CLASS grid cell is independent with no lateral transfers of heat or moisture (however, CLASS has been incorporated into the MEC-Surface & Hydrology System (MESH) framework that does allow lateral transfers (Pietroniro et al., 2007)16.

  1. Verseghy, D. L.: CLASS – A Canadian land surface scheme for GCMs. I. Soil model, Int. J. Climatol., 11(2), 111–133, 1991. ↩︎

  2. Verseghy, D. L., McFarlane, N. A. and Lazare, M.: CLASS – A Canadian land surface scheme for GCMs, II. Vegetation model and coupled runs, Int. J. Climatol., 13(4), 347–370, 1993. ↩︎

  3. Verseghy, D. L.: The Canadian land surface scheme (CLASS): Its history and future, Atmosphere-Ocean, 38(1), 1–13, 2000. ↩︎

  4. Verseghy, D.: CLASS – The Canadian land surface scheme, Climate Research Division, Science and Technology Branch, Environment Canada., 2017. ↩︎

  5. Bailey, W. G., Saunders, I. R., Bowers, J. D. and Verseghy, D. L.: Application of the Canadian land surface scheme to a full canopy crop during a drying cycle, Atmosphere-Ocean, 38(1), 57–80, 2000. ↩︎

  6. Kothavala, Z., Arain, M. A., Black, T. A. and Verseghy, D.: The simulation of energy, water vapor and carbon dioxide fluxes over common crops by the Canadian Land Surface Scheme (CLASS), Agric. For. Meteorol., 133(1–4), 89–108, 2005. ↩︎

  7. Roy, A., Royer, A., Montpetit, B., Bartlett, P. A. and Langlois, A.: Snow specific surface area simulation using the one-layer snow model in the Canadian LAnd Surface Scheme (CLASS), The Cryosphere, 7(3), 961–975, 2013. ↩︎

  8. Bartlett, P. A., MacKay, M. D. and Verseghy, D. L.: Modified snow algorithms in the Canadian land surface scheme: Model runs and sensitivity analysis at three boreal forest stands, Atmosphere-Ocean, 44(3), 207–222, 2006. ↩︎

  9. Brown, R., Bartlett, P., MacKay, M. and Verseghy, D.: Evaluation of snow cover in CLASS for SnowMIP, Atmosphere-Ocean, 44(3), 223–238, 2006. ↩︎

  10. Wu, Y., Verseghy, D. L. and Melton, J. R.: Integrating peatlands into the coupled Canadian Land Surface Scheme (CLASS) v3.6 and the Canadian Terrestrial Ecosystem Model (CTEM) v2.0, Geoscientific Model Development, 9(8), 2639–2663, 2016. ↩︎

  11. Verseghy, D. L. and MacKay, M. D.: Offline Implementation and Evaluation of the Canadian Small Lake Model with the Canadian Land Surface Scheme over Western Canada, J. Hydrometeorol., 18(6), 1563–1582, 2017. ↩︎

  12. Melton, J. R., Verseghy, D. L., Sospedra-Alfonso, R. and Gruber, S.: Improving permafrost physics in the coupled Canadian Land Surface Scheme (v. 3.6.2) and Canadian Terrestrial Ecosystem Model (v. 2.1) (CLASS-CTEM), Geosci. Model Dev. Discuss., 1–73, 2019. ↩︎

  13. Ganji, A., Sushama, L., Verseghy, D. and Harvey, R.: On improving cold region hydrological processes in the Canadian Land Surface Scheme, Theor. Appl. Climatol., 127(1-2), 45–59, 2015. ↩︎

  14. Paquin, J.-P. and Sushama, L.: On the Arctic near-surface permafrost and climate sensitivities to soil and snow model formulations in climate models, Clim. Dyn., 44(1-2), 203–228, 2014. ↩︎

  15. Scinocca, J. F., Kharin, V. V., Jiao, Y., Qian, M. W., Lazare, M., Solheim, L., Flato, G. M., Biner, S., Desgagne, M. and Dugas, B.: Coordinated Global and Regional Climate Modeling, J. Clim., 29(1), 17–35, 2016. ↩︎

  16. Pietroniro, A., Fortin, V., Kouwen, N., Neal, C., Turcotte, R., Davison, B., Verseghy, D., Soulis, E. D., Caldwell, R., Evora, N. and Pellerin, P.: Development of the MESH modelling system for hydrological ensemble forecasting of the Laurentian Great Lakes at the regional scale, Hydrol. Earth Syst. Sci., 11(4), 1279–1294, 2007. ↩︎