Snowmelt → Energy Balance MethodThe input variables for the Energy Balance method of estimating runoff due
to snowmelt are defined as follows:
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. Note: If net total radiation has been measured, it can be entered as QSW and then QLW can be set to zero. Any meteorological variables entered here (such as Tair) are automatically shared with other other processes, such as Evapotranspiration and Precipitation. Equations Used by the Energy-Balance Method
Notes on the EquationsThe cold content of the snow pack, Ecc, represents an energy deficit that must be overcome before snow begins to melt. First, Qnet is computed as the sum of all energy fluxes (the Q's). Wherever (Qnet < 0 and hsnow > 0) the snow cools and the cold content increases. Similarly, wherever (Qnet > 0 and hsnow > 0) the snow warms and the cold content decreases. In both cases the cold content changes according to: Ecc = [Ecc - (Qnet * dt)] and we have M=0 as long as (Ecc > 0). However, if warming continues long enough to consume the cold content (so that Ecc drops to zero), then the snow begins to melt (M > 0). In this case the meltrate is given by M = Qnet / (ρwater * Lf). ReferencesBrutsaert, W. (1975) On a derivable formula for long-wave radiation from clear skies, Water Resources Research, 11, 742-744. Dingman, S.L (2002) Physical Hydrology, 2nd ed., Prentice Hall, New Jersey. (see Chapter 7, pp. 285-299) Schlicting, H. (1960) Boundary Layer Theory, 4th ed., McGraw-Hill, New York, 647 pp. 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. |