Also known as
Model type Single
Model part of larger framework
Incorporated models or components:
Spatial dimensions 2D
Spatial extent Landscape-Scale, Watershed-Scale
Model domain Hydrology
One-line model description Snowmelt process component (Degree-Day method) for a D8-based, spatial hydrologic model
Extended model description This process component is part of a spatially-distributed hydrologic model called TopoFlow, but it can now be used as a stand-alone model.


First name Scott
Last name Peckham
Type of contact Model developer
Institute / Organization CSDMS, INSTAAR, University of Colorado
Postal address 1 1560 30th street
Postal address 2
Town / City Boulder
Postal code 80305
State Colorado
Country United States
Email address
Phone 303-492-6752

Supported platforms Unix, Linux, Mac OS, Windows
Other platform
Programming language Python
Other program language None (but uses NumPy package)
Code optimized Single Processor
Multiple processors implemented
Nr of distributed processors
Nr of shared processors
Start year development 2001
Does model development still take place? Yes
If above answer is no, provide end year model development
Code development status Active
When did you indicate the 'code development status'? 2020
Model availability As code, As teaching tool
Source code availability
(Or provide future intension)
Through web repository
Source web address
Source csdms web address
Program license type Apache public license
Program license type other
Memory requirements Standard
Typical run time Minutes to hours

Describe input parameters The input variables used for the Degree-Day method of estimating runoff due to snowmelt are defined as follows:
c_0 	= coefficient
T_0 	= threshold temperature (deg C)
T_air 	= air temperature (deg C)
ρ_snow 	= density of the snow (kg / m^3)
ρ_water = density of liquid water, 1000 (kg / m^3)
h0_snow = initial snow depth (m)
h0_swe 	= initial depth, snow water equivalent (m)

The behavior of this component is controlled with a configuration (CFG) file, which may point to other files that contain input data. Here is a sample configuration (CFG) file for this component:

Method code:            0
Method name:            Degree-Day
Time step:              Scalar         3600.00000000           (sec)
Cp_snow:                Scalar         2090.00000000           (J/kg/K)
rho_snow:               Scalar         300.00000000            (kg/m^3)
c0:                     Scalar         2.70000005              (mm/day/deg C)
T0:                     Scalar         -0.20000000             (deg C)
h0_snow:                Scalar         0.50000000              (m)
h0_swe:                 Scalar         0.15000000              (m)
Save grid timestep:     Scalar         60.00000000             (sec)
Save mr grids:          0              Case5_2D-SMrate.rts     (m/s)
Save hs grids:          0              Case5_2D-hsnow.rts      (m)
Save sw grids:          0              Case5_2D-hswe.rts       (m)
Save cc grids:          0              Case5_2D-Ecc.rts        (J/m^2)
Save pixels timestep:   Scalar         60.00000000             (sec)
Save mr pixels:         0              Case5_0D-SMrate.txt     (m/s)
Save hs pixels:         0              Case5_0D-hsnow.txt      (m)
Save sw pixels:         0              Case5_0D-hswe.txt       (m)
Save cc pixels:         0              Case5_0D-Ecc.txt        (J/m^2)
Input format ASCII, Binary
Other input format
Describe output parameters
Output format ASCII, Binary
Other output format
Pre-processing software needed? Yes
Describe pre-processing software Another program must be used to create the input grids. This includes a D8 flow grid derived from a DEM for the region to be modeled. The earlier, IDL version of TopoFlow can be used to create some of these.
Post-processing software needed? Yes
Describe post-processing software None, except visualization software. Grid sequences saved in netCDF files can be viewed as animations and saved as movies using VisIt.
Visualization software needed? Yes
If above answer is yes
Other visualization software VisIt

Describe processes represented by the model The Degree-Day method for modeling Snowmelt.
Describe key physical parameters and equations Equations Used by the Degree-Day Method
M 	 = (c_0 / 86400) * (T_air - T_0) 	= meltrate (mm / sec)
M_max 	 = (1000 * h_snow / dt) * (ρ_water / ρ_snow) 	= max possible meltrate (mm / sec)
dh_snow  = M * (ρ_water / ρ_snow) * dt 	= change in snow depth (m)
Describe length scale and resolution constraints Recommended grid cell size is around 100 meters, but can be parameterized to run with a wide range of grid cell sizes. DEM grid dimensions are typically less than 1000 columns by 1000 rows.
Describe time scale and resolution constraints The basic stability condition is: dt < (dx / u_min), where dt is the timestep, dx is the grid cell size and u_min is the smallest velocity in the grid. This ensures that flow cannot cross a grid cell in less than one time step. Typical timesteps are on the order of seconds to minutes. Model can be run for a full year or longer, if necessary.
Describe any numerical limitations and issues This model/component needs more rigorous testing.

Describe available calibration data sets This model/component is typically not calibrated to fit data, but is run with a best guess or measured value for each input parameter.
Upload calibration data sets if available:
Describe available test data sets Available test data sets:
  • Treynor watershed, in the Nishnabotna River basin, Iowa, USA.
  • (Two large rainfall events.)
  • Small basin in Kentucky.
  • Inclined plane for testing.
  • Arctic watershed data from Larry Hinzman (UAF).
  • See /data/progs/topoflow/3.0/data on CSDMS cluster.
Upload test data sets if available:
Describe ideal data for testing Several test datasets are stored on the CSDMS cluster at: /data/progs/topoflow/3.0/data.

Do you have current or future plans for collaborating with other researchers? Collaborators include: Larry Hinzman (UAF), Bob Bolton, Anna Liljedahl (UAF), Stefan Pohl and others
Is there a manual available? Yes
Upload manual if available:
Model website if any This site.
Model forum / discussion board
Comments About this component:
  • This component was developed as part of the TopoFlow hydrologic model, which was originally written in IDL and had a point-and-click GUI. For more information on TopoFlow, please goto:
  • When used from within the CSDMS Modeling Tool (CMT), this component has "config" button which launches a graphical user interface (GUI) for changing input parameters. The GUI is a tabbed dialog with a Help button at the bottom that displays HTML help in a browser window.
  • This component also has a configuration (CFG) file, with a name of the form: <case_prefix>_channels_diff_wave.cfg. This file can be edited with a text editor.
  • The Numerical Python module (numpy) is used for fast, array-based processing.
  • This model has an OpenMI-style interface, similar to OpenMI 2.0. Part of this interface is inherited from "".

Model info
Nr. of publications: 1
Total citations: 7
h-index: 1
Qrcode TopoFlow-Snowmelt-Degree-Day.png
Link to this page




Nr. of publications: 1
Total citations: 7
h-index: 1




Input Files

Output Files