1. Please write down the name (and abbreviation) of your snow model or land-surface model with snow component?


Canadian Land Surface Scheme for GCMs (CLASS) (1D stand-alone version 2.6)


2. Name and address of model developer;

Dr. Diana Verseghy

Atmospheric Environment Service

Downsview, Ontario


M3H 5T4


3. Name and address of model user;


Ross Brown

Atmospheric Environment Service

2121 Trans-Canada Highway

Dorval, Qc


H9P 1J3


4. Please indicate whether your model is developed for application

As a land surface scheme for coupling to atmospheric models (RCMs, GCMs and NWP)


5. The first year when the model was used;


First results published in Verseghy (1991) - Intl. J. Climatology, Vol. 11:111-133

6. One paragraph description of your model (e.g. abstract from report or paper);

A land surface scheme incorporating three soil layers, a snow layer, and a vegetation canopy with physically-based calculations of heat and moisture transfers at the surface and across layer boundaries. Snow is treated as a variable depth fourth ‘soil’ layer and snow-covered and snow-free areas are treated separately. Canopy snow processes (interception, sublimation, and melt) are also treated in CLASS. The energy balance equation is solved iteratively for the surface temperature and the surface infiltration rate is calculated using a simplified theoretical analysis which allows for surface ponding and runoff.

7. Please specify any known application range or restrictions;


8. What are the development data needs?


9. What are the operational data needs?


10.Please indicate with an "x" for those meteorological variables used to DRIVE your snow model?


precipitation :x

air temperature :x

wind speed :x

wind direction :

humidity :x

downwelling shortwave radiation :x

downwelling longwave radiation :x (or net longwave)

cloud cover :

surface pressure :


11. List the state variables (e.g., snow temperature, snow water equivalent, etc) your snow model uses?

snow temperature

snow mass (water equivalent)

snow density

snow albedo

snow depth

snow transmissivity


12. List the measurable/adjustable parameters (e.g., snow surface aerodynamic roughness, maximum albedo at visible wavelength, etc, excluding initial conditions) your snow model uses?



13. What are the output data?


( same as 11 with exception of snow depth and transmissivity)


14. What computer language does your model use?




15. How many subroutines (or functions) does your snow model have?


?? many!


16. Number of lines of the snow code?


?? numerous!


17. What is the recommended hardware?


UNIX server (can run on PC)


18. How does your model determine the form of precipitation

(i.e., snowfall and rainfall)?

Please give the formulation.


Diagnosed based on 0 deg. C threshold (default) - can be readily replaced with any user-defined parameterization or by observed precipitation phase.


19. Is your snow model one dimensional or multi-dimensional?

Please specify.


Can be run in 1-D stand-alone mode or coupled to atmospheric model


20. If one dimensional, how many layers are there in your snow model?

Please specify layering structure.


One layer


21. What is your snow model time step?


1800 s (specified by user)


22. Does your model snow albedo allow its

spectral differences (visible vs. near-IR)? Yes

directional differences (direct vs. diffuse)? No



23. Is your model snow albedo a function of

snow age Yes

grain size

solar zenith angle Yes


snow depth? Yes


24. Does your snow model explicitly treat liquid water retention and percolation within the snowpack?




25. Does your snow model account for changes in the hydraulic and thermal properties of snow due to meltwater refreezing?




26. Is snow density in your snow model changing with time or fixed?


Snow density function of time


27. Is heat capacity and conductivity in your snow model changing with time or fixed?


Snow thermal properties are functions of snow density


28. Does your snow model simulate vapor transfer in the snowpack?


Not within the pack i.e. no simulation of depth hoar


29. Does your snow model account for the heat transfer between the bottom of the snowpack and the underlying soil?




30. In snow energy balance, does your model consider heat convected by rain or falling snow?




31. Does your snow model include snow drifting and redistribution by wind (or avalanche)? If so, how?




32. How is areal snow distribution treated?


Not treated in 1-D version


33. Does your snow model account for sub-grid (or sub-watershed) effects of topography? No


If so, how is temperature distributed?

how is precipitation (spatial, elevation and corrections) distributed?

how is solar radiation distributed?

how is wind distributed?

how are other meteorological variables distributed?

34. Does your snow model consider snow-vegetation interaction?




35. Does the snow-vegetation interaction account for

different vegetation types (grass vs. forest), Yes

different vegetation heights (short vs. tall), Yes

different vegetation densities (small vs. large LAI), Yes

different vegetation coverages (sparse vs. dense vegetation)?



36. Are snow interception, drip and melt on canopy surface allowed in your model?




37. How is the upper limit of the canopy interception determined?




38. In the presence of vegetation, how is snow surface albedo altered?


Albedo partitioned between snow-covered and non-snow covered portions of surface until snow depth reaches a vegetation masking depth.


39. In the presence of vegetation, how is snow surface roughness altered?



40. In the presence of forest, does your snow model allow spatial variability of snow depth and water equivalent on forest floor?


n/a for 1-D version


41(a). How does your model deliver snowmelt to the soil system (e.g. affecting soil moisture)?




(b). Once snowmelt is generated, how does your model relate it to runoff?


?? excess water over infiltration rate and storage capacity


42. How is frozen soil treated in your model?

Ice fraction changes thermal properties…

43. Has your snow model been tested with the field data?




Is so, what data? Col de Porte and Goose Bay

what are their temporal and spatial scales? Daily snow depth, weekly swe


44. Has your snow model been used together with remote sensing data as input?




If so, how?


45. If your snow model is coupled with a numerical weather forecasting model or climate model, has the model snow product been compared with satellite data?


Yes - Foster et al. (1996), J. Climate, 9:409-426.


If so, what satellite data were used?


Passive microwave (SMMR and SSMI) and NOAA visible.


46. Please list any other previous applications.


47. Please specify verification criteria, if any?

Bias, rmse (monthly snow depth and swe)

Correlation between observed and simulated monthly snow statistics for multiple years.


48. What are the model fitting procedures, if any?


49. What are future plans for using/improving the model?

Further validation as part of SNOWMIP comparison study.

50. Please provide references relevant to the model description and use.

Verseghy, D.L., 1991: CLASS - A Canadian land surface scheme for GCMs. I. Soil Model. Intl. J. Climatology, 11, 111-133.

Verseghy, D.L., N.A. McFarlane and M. Lazare, 1993: CLASS - A Canadian Land Surface Scheme for GCMs. Part II: Vegetation model and coupled runs, Intl. J. Climatology, 13, 347-370.

Foster, J., G. Liston, R. Koster, R. Essery, H. Behr, L. Dumenil, D. Verseghy, S. Thompson, D. Pollard, J. Cohen, 1996: Snow cover and snow mass intercomparisons of general circulation models and remotely sensed datasets, J. Clim., 9, 409-426.

-- Last updated Wed March 24 09:35:00 MST 1999 by Zong-Liang Yang.
For questions and comments, please contact Zong-Liang Yang