There are five soil parameters that comprise the set of variables to rely on for model calibration. More detailed descriptions of each parameter are included in the VIC Soil Parameter File documentation. These parameters, their typical ranges, and a short description of the effect of each one on simulated hydrographs follows.
Ds - [>0 to 1] This is the fraction of Dsmax where non-linear (rapidly increasing) baseflow begins. With a higher value of Ds, the baseflow will be higher at lower water content in lowest soil layer.
Dsmax - [>0 to ~30, depends on hydraulic conductivity] This is the maximum baseflow that can occur from the lowest soil layer (in mm/day).
Ws - [>0 to 1] This is the fraction of the maximum soil moisture (of the lowest soil layer) where non-linear baseflow occurs. This is analogous to Ds. A higher value of Ws will raise the water content required for rapidly increasing, non-linear baseflow, which will tend to delay runoff peaks.
binf - [>0 to ~0.4] This parameter defines the shape of the Variable Infiltration Capacity curve. It describes the amount of available infiltration capacity as a function of relative saturated gridcell area. A higher value of binf gives lower infiltration and yields higher surface runoff.
Soil Depth (of each layer) - [typically 0.1 to 1.5 meters] Soil depth effects many model variables. In general, for runoff considerations, thicker soil depths slow down (baseflow dominated) seasonal peak flows and increase the loss due to evapotranspiration.
Although other input parameters can be adjusted (such as snow albedo) these are the primary ones to use. Only in particularly stubborn cases should other parameters be adjusted.