  Process-based hydrologic models allow to identify the behavior of a basin
providing a mathematical description of the hydrologic processes underlying the
runoff mechanisms that govern the streamflow generation. This study focuses on
a macroscale application of the Variable Infiltration Capacity (VIC) model over
31 headwater subwatersheds belonging to the Duero River Basin, located in the
Iberian Peninsula, through a three-part approach: (1) the calibration and
validation of the VIC model for all the subwatersheds; (2) an integrated
sensitivity analysis concerning the soil parameters chosen for the calibration,
and (3) an assessment of equifinality and the efficiency of the calibration
algorithm. The calibration and validation processes showed good results for
most of the subwatersheds in a computationally efficient way using the
Shuffled-Complex-Evolution algorithm. The sensitivity measures were obtained
with the Standardized Regression Coefficients method through a post-process of
the outputs of a Monte Carlo simulation carried out for 10 000 parameter
samples for each subwatershed. This allowed to quantify the sensitivity of the
water balance components to the selected parameters for the calibration and
understanding the strong dependencies between them. The final assessment of the
equifinality hypothesis manifested that there are many parameter samples with
performances as good as the optimum, calculated using the calibration
algorithm. For almost all the analyzed subwatersheds the calibration algorithm
resulted efficient, reaching the optimal fit. Both the Monte Carlo simulation
and the use of a calibration algorithm will be of interest for other feasible
applications of the VIC model in other river basins.
