Soil Moisture
                            ---- --------

The soil moisture is expressed as a fraction.  For example, if the
soil moisture is 0.2 in the 0-10 cm layer, then this layer has 2 cm 
of water.

The saturation value of soil moisture is 0.477 and the field capacity
is 0.358 (75% of saturation).  The soil moisture can exceed field
capacity during heavy rains; however, the value will quickly reach
field capacity.  The wilting value is set at 0.1.

The soil depth (layer depth) and field capacity are horizontally uniform
which is a limitation.

The "Mahrt and Pan" (1984) and "Pan and Mahrt" (1987) papers
describe a gravitational percolation through the bottom layer.
The ground water flow out of the model was added to the surface 
runoff term so that one could calculate a water budget.

Note: values also apply to the model for Reanalysis 2.