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The procedure for calibrating the model was to use multipliers to
vary the desired parameters of the model. This calibration focused
upon the effect of the hydraulic diffusivity of the soil (Dj_) and the
surface heat (h^) and mass (hm) coefficients primarily due to the
uncertainty of their values used during the validation phase of
modeling. A sensitivity analysis was performed by running the
simulation using several values of the multiplier for hydraulic
diffusivity, then selecting a value for the remaining calibration which
seemed to provide the least deviation between evaporation rates and
soil surface temperature. Since the calculation of the two surface
coefficients were derived from the same basic equations and are
proportional to each other, then a single multiplier was utilized for
both the heat and mass transfer coefficients. All other soil
properties such as heat capacity, thermal conductivity, soil water
potential and diffusivity of water vapor were allowed to vary according
to the temperature and water content of the soil as described in
Chapter II. This sensitivity analysis and calibration procedure was
used primarily to establish limits of values of the multipliers for
more precise calibration in future research efforts.
Sensitivity analysis for the effect of varying the hydraulic
diffusivity upon evaporation and soil temperature was conducted first.
Multipliers for the hydraulic diffusivity were 0.5, 2.0 and 5.0 and
shifted the relationship of diffusivity to water content vertically and
did not make any shifts with respect to water content (Figure 5-21).
Very little difference was seen in the simulated cumulative evaporation
using the hydraulic diffusivity multipliers of 2 and 5 until the
beginning of the third day of the simulation (January 7), at which time