The Snow AccretionDepletion Module is also used to predict the amount of water
available from snowmelt. If the ground surface is frozen, the meltwater is assumed to run
off and the moisture content of the soil is unchanged. If there is a thawed layer, the
moisture content of the soil increases, as the meltwater infiltrates the soil. If the Snow
AccretionDepletion Module is not being used to calculate the amount of meltwater from
the snowpack, then the available water (cm) is assumed to be 0.28 times the change in
thickness of the snow cover (cm). A factor of 0.28 instead of 0.33 is used to allow for the
likelihood that some of the water in the snowpack evaporates and some of it runs off once
the thawed soil layer is near saturation.
1.2 Basic Program Format
The individual models comprising FASST are grouped into nine modules. These modules
accomplish the following tasks:
1. Read in the meteorological data and make any necessary unit conversions and
assumptions. (Chapter 9)
2. If the solar or infrared flux information is missing, generate the appropriate values
based on the cloud amount and type for all required flux information except the
ground emitted IR flux, which is dependent on the surface temperature. (Chapters
2 and 3)
3. Read in the control file containing information concerning initial conditions, soil
profile, and meteorological data. (Chapter 9)
4. Initialize the soil profile and the state of the ground. (Chapter 10)
START OF MAIN CALCULATION LOOP
5. Calculate the emitted and net IR fluxes. (Chapter 3)
6. Calculate the soil temperature and volumetric moisture content profiles. (Chapters
4 and 5)
7. Check for freezing and/or thawing. Calculate the soil strength. (Chapters 5 and 6)
8. If there is snow or ice on the ground, check to see if it is melting or accumulating.
If it is melting, calculate the corresponding amount of runoff. (Chapters 7 and 8)
9. Check the calculation time increment, update as necessary.
END OF MAIN CALCULATION LOOP
10. Output the results.