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

Utah energy balance snow accumulation and melt model (UEB)

2. Name and address of model developer;

David Tarboton                     Email: dtarb@cc.usu.edu
Associate Professor                Ph: 801-797-3172
Utah Water Research Laboratory     Fax: 801-797-1185
Civil and Environmental Engineering
Utah State University, Logan UT 84322-4110

3. Name and address of model user;

David Tarboton
Utah State University

4. Please indicate whether your model is developed for application

   in understanding snow processes,     X  
   in a runoff forecasting model,	X 
   in a weather forecasting model,   
   in a global climate model (GCM),         
   or other (please specify)?           X
      For understanding snow processes and for runoff, erosion 
      and water balance forecasting and modeling.

5. The first year when the model was used;


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

The snow model used was the Utah Energy Balance (UEB) model (Tarboton et al., 1995; Tarboton and Luce, 1996) which represents the snowpack at each point on a grid over the watershed in terms of two state variables, water equivalence and energy content. A third state variable is used to quantify the snow surface age, used for albedo calculations. The use of only three state variables makes the model parsimonious and suitable for application at each grid cell within a distributed hydrological model. The model uses a parameterization of surface heat flux into the snow based on the difference between the snow surface and average snowpack temperatures to balance external energy fluxes at the snow surface and calculate snow surface temperature without introducing additional state variables.

7. Please specify any known application range or restrictions;

8. What are the development data needs;

Slope, aspect, elevation, vegetation (Canopy closure and height/rougness) at each point the model is applied.

9. What are the operational data needs?

See 10. Below.

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
   cloud cover                     : 
   surface pressure                : X 

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

Snow Water Equivalence
Energy Content
Dimensionless age of the surface

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?

Snow surface thermal conductance
Snow saturated hydraulic conductivity
Snow surface roughness
Maximum albedo at visible wavelength.
[These were adjusted in initial model development and calibration 
but are intended to be held at the fixed values obtained for other 

13. What are the output data?

Melt Outflow
Updated state variables
Surface temperature
All energy and mass fluxes to and from the snow.

14. What computer language does your model use?


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

About 10

16. Number of lines of the snow code?

About 600

17. What is the recommended hardware?

Any with a Fortran compiler - Has been successfully run on Sun Solaris, IBM RS6000 and Intel 486 and Pentium hardware.

18. How does your model determine the form of precipitation (i.e., snowfall and rainfall)? Please give the formulation.

Precip is rain if Air Temperature > 3 C Precip is snow if Air temperature < -1 C Precip is mixed with linear mixture if Tepmperature within this range

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


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

1 layer

21. What is your snow model time step?

Flexible but longer than 6 hours not recommended. The diurnal cycle is important and 6 hours is the minimum to have half a chance at representing the diurnal cycle.

22. Does your model snow albedo allow its

    spectral differences    (visible vs. near-IR)? 
    directional differences (direct  vs. diffuse)? 

23. Is your model snow albedo a function of

      snow age                  X
      grain size                  
      solar zenith angle        X
      snow depth?               X

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?


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


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


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

Yes in a rough way

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?

Yes - Through a factor that multiplies snowfall.

32. How is areal snow distribution treated?

The model may be run on a grid.

33. Does your snow model account for sub-grid (or sub-watershed) effects of topography? If so, how is temperature distributed?

The model may be run on a grid. Temperature may be input whatever you like at each grid point. We have used various interpolation and lapse rate schemes.

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

This is treated outside the snow model. Again various interpolation schemes have been tried.

how is solar radiation distributed?

Measurements used to estimate atmospheric transmissivity which is then used to compute slope, aspect and shading adjusted incident radiation.

how is wind distributed?

Spatially interpolated.

how are other meteorological variables distributed?

Spatially interpolated

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

Not yet.

35. Does the snow-vegetation interaction account for

 different vegetation types     (grass vs. forest), 
 different vegetation heights   (short vs. tall),  
 different vegetation densities (small vs. large LAI),        
 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?

Based upon snow 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?

Yes - by running on a grid with different canopy densities.

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

It just delivers it.

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

A separate topographically based runoff model is used to deal with the disposition of snowmelt.

42. How is frozen soil treated in your model?

The energy content state variable includes the top 40 cm of soil.

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


If so, what data? (areas)

what are their temporal and spatial scales?

See the report: Tarboton, D. G. and C. H. Luce, (1996), "Utah Energy Balance Snow Accumulation and Melt Model (UEB)," Computer model technical description and users guide, Utah Water Research Laboratory and USDA Forest Service Intermountain Research Station. This is available from http://www.engineering.usu.edu/dtarb/

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? If so, what satellite data were used?

46. Please list any other previous applications.

47. Please specify verification criteria, if any?

See report in answer to 43.

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

See report in answer to 43.

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

Given time and money I'd like to do the following:
1.  Testing in paired open and forest situation.
2.  Address problems matching internal energy to measured internal 
3.  Revise the treatment of vegetation to include more physical
    representation of radiation penetration through canopies and 
    energy exchanges within and between snow and canopy.
4.  Evaluate benefit to be had from including variable surface density 
    and hence snow thermal conductivity in the model.

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

Tarboton, D. G. and C. H. Luce, (1996), "Utah Energy Balance Snow Accumulation and Melt Model (UEB)," Computer model technical description and users guide, Utah Water Research Laboratory and USDA Forest Service Intermountain Research Station. See also http://www.engineering.usu.edu/dtarb/

-- Last updated Fri Oct 8 12:47:54 MST 1999 by Zong-Liang Yang.
For questions and comments, please contact Zong-Liang Yang