Land surface hydrologic models are commonly evaluated based upon the degree of correspondence between measured and modeled discharge. In this paper we illustrate significant shortcomings associated with the simple discharge based evaluation strategy. A standard conceptual hydrologic model is applied within a Monte Carlo framework to two catchments representing significantly different hydrologic regimes. Time source hydrograph separations are derived, in addition to modeled discharge, and used to more completely characterize model functioning, across the entire a priori parameter distribution. The inclusion of hydrograph separation results in improved characterization of parameter uncertainty, and in one of the cases, complete model rejection.