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

SOIL

2. Name and address of model developer;

Per-Erik Jansson
SLU, Department of Soil Sciences
Box 7014
750 07 Uppsala
Sweden

3. Name and address of model user;

Manfred Stähli & Per-Erik Jansson
SLU, Department of Soil Sciences
Box 7014
750 07 Uppsala
Sweden
Tel: ..46 - 18 67 29 29        Fax: ..46 - 18 67 27 95
WWW: http://www.ito.umnw.ethz.ch/SoilPhys/staff/staehli/manfred.htm

4. Please indicate whether your model is developed for application

   in understanding snow processes,   X
   in a runoff forecasting model,	 
   in a weather forecasting model,   
   in a global climate model (GCM),         
   or other (please specify)?         X  
      in understanding snow and frozen soil processes

5. The first year when the model was used;

1979

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

The SOIL-model is calculating combined heat and water fluxes in the (one-dimensional) soil-snow-atmosphere system. The two basic assumptions for the soil are the Richards-equation (Richards, 1931) for water flow and Fourier's law for heat flow. Standard meteorological data are used as inputs, and the boundaries are determined by formulations of interception, drainage flow, percolation and geothermal heat flux. For the description of those parts of the model which are not focused by the present study it is referred to Jansson (1996) or Johnsson & Jansson (1991).

7. Please specify any known application range or restrictions;

The model is a point model, that means it does not account for variations in the landscape. The model is focusing on the dynamics in the soil. Therefore the snow part is kept rather simplistic.

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 radiation) (optionally)
   cloud cover                     : X (optionally)
   surface pressure                :   

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

snow water equivalent
snow density
snow surface temperature
snow depth

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?

density of new-fallen snow
retention capacity of snow
thermal conductivity coefficient
rain temperature threshold
snow temperature threshold
temperature and radiation coefficients in snow melt function

13. What are the output data?

snow depth
snow water equivalent
snow surface temperature
soil surface temperature
sensible heat flux from snow pack
latent heat flux from snow pack
snow density
snow age
snow albedo

14. What computer language does your model use?

FORTRAN

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

The whole SOIL-model has about 77 subroutines, one of which is the snow-subroutine.

16. Number of lines of the snow code?

ca. 100

17. What is the recommended hardware?

PC

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

You can specify with a parameter the threshold air temperature below which all precipitation falls as snow, and with a parameter the threshold air temperature above which all precipitation falls as rain. Between those values mixed precipitation is assumed.

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

One dimensional

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?

It is set by the user, often hourly or daily inputs.

22. Does your model snow albedo allow its

    spectral differences    (visible vs. near-IR)? 
      No.
    directional differences (direct  vs. diffuse)? 
      No.

23. Is your model snow albedo a function of

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

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

Water transfer within the snowpack is not considered. A certain retention capacity of the snowpack is assumed. When it is exceeded the water is infiltrating to the soil or running of on the soil surface.

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

No.

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

It is changing with time.

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

Heat conductivity is a function of snow density, so it is also changing with time.

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

No.

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

Yes.

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

No.

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

No.

32. How is areal snow distribution treated?

The model is one dimensional.

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

NA.

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?

Yes, snow interception on vegetation. (simplistic approach)

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),          X
 different vegetation coverages (sparse vs. dense vegetation)?

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

interception: yes

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

The interception storage capacity per LAI unit is a model parameter.

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

Not altered by vegetation.

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

Not altered.

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

No.

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

A certain retention capacity of the snowpack is assumed. When it is exceeded the water is infiltrating to the soil or running of on the soil surface.

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

The infiltration capacity of the soil is determined by the volume of air-filled pores in the uppermost soil layer and a hydraulic conductivity of this layer. If the infiltration capacity is exceeded by the snowmelt it starts to run off on the surface.

42. How is frozen soil treated in your model?

Very advanced. The main focus of the model is on soil processes.

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

Yes, two winter seasons in Central Sweden, plot measurements.

If so, what data? (areas)

what are their temporal and spatial scales?

Snow temperatures, soil temperatures, soil water content:
     (continuously, 1 hour resolution).
Snow depth: daily (or weekly if unchanged).
Snow density: some few occasions

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

No.

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?

No.

46. Please list any other previous applications.

Many applications on water and heat dynamics in frozen soils where the snow part was a kind of "boundary conditions" (see below references).

47. Please specify verification criteria, if any?

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

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

A research student is starting developping the snow part of the SOIL model: he will introduce a multi-layer system including water redistribution within the snow layers. He will also test the snow surface energy balance approach. The model will be used within a EC-project on water and energy exchange in the boreal landscape (WINTEX).

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

Jansson, P.-E. 1991: Simulation model for soil water and heat conditions. Description of the SOIL model, Swed. Univ. of Agric. Sci., Dep. of Soil Sci. Report 165.

Other references:

Jansson, P.-E. & Gustafsson, A. 1987: Simulation of surface runoff and pipe discharge from an agricultural soil in northern Sweden, Nordic Hydrology, 18, 151-166.

Johnsson, H. & Lundin, L.-C. 1991: Surface runoff and soil water percolation as affected by snow and soil frost, Journal of Hydrology, 122, 141-159.

Stadler, D. 1996: Water and solute dynamics in frozen fores soils - measurements and modelling, Dissertation ETH No., ETH Zurich.

Stähli, M., Jansson, P.-E. and Lundin, L.-C. 1996: Preferential water flow in a frozen soil - a two-domain model approach, Hyd. Proc., 10, 1305-1316.

Stähli, M. & Stadler, D. 1997. 'Measurement of water and solute dynamics in freezing soil columns with time domain reflectometry', Journal of Hydrology, 195: 352-369.

Stähli, M. & Jansson, P.-E. 1998. 'Test of two SVAT snow submodels during different winter conditions', Agricultural and Forest Meteorology, (accepted for publication).

Stähli, M., Jansson, P.-E. & Lundin, L.-C. 1998. 'Soil moisture redistribution and infiltration in frozen sandy soils', Submitted to Water Resources Research.