Snowmelt → Degree-Day Method

The input variables used for the Degree-Day method of estimating runoff due to snowmelt are defined as follows:

c0 = coefficient
T0 = threshold temperature [deg C]
Tair = air temperature [deg C]
ρsnow = density of the snow [kg / m3]
ρwater = density of liquid water, 1000 [kg / m3]
h0snow = initial snow depth [m]
h0swe = initial depth, snow water equivalent [m]

For each variable, you may choose from the droplist of data types. For the "Scalar" data type, enter a numeric value with the units indicated in the dialog. For the other data types, enter a filename. Values in files must also have the indicated units.

Single grids and grid sequences are assumed to be stored as RTG and RTS files, respectively. Time series are assumed to be stored as text files, with one value per line. For a time series or grid sequence, the time between values must coincide with the timestep provided.

A Tair variable entered here is automatically shared with other processes such as Evapotranspiration and Precipitation.


Equations Used by the Degree-Day Method

M = (c0 / 86400) * (Tair - T0) = meltrate [mm / sec]
Mmax = (1000 * hsnow / dt) * (ρwater / ρsnow) = max possible meltrate [mm / sec]
dhsnow = M * (ρwater / ρsnow) * dt = change in snow depth [m]


References

Zhang, Z., D.L. Kane and L.D. Hinzman (2000) Development and application of a spatially-distributed Arctic hydrological and thermal process model (ARHYTHM), Hydrological Processes, 14, 1017-1044.