A CONCEPTUAL-MODEL OF CATCHMENT WATER-BALANCE .1. FORMULATION AND CALIBRATION

A conceptual model of a catchment's annual water balance is developed. The model is based on the sequential separation of annual precipitation into surface runoff and wetting, and wetting into baseflow and vaporization. The separation is based on a proportional relation linking the three variables involved at each step. The generic form of the proportional relation is (X - lambda Z(p) - Y)/[(1 - lambda)Z(p)] = Y/(X - lambda Z(p)), in which X is an independent variable, Y is a dependent variable, X is the initial abstraction coefficient, and Z(p) is the potential value of the difference Z = X - Y. Given a set of model parameters, the method can be used to separate annual precipitation into its three major components: surface runoff, baseflow, and vaporization. Initial application of the method to literature catchment data provided encouraging results. The method can be used for estimates of the annual water yield throughout the climatic spectrum. The model parameters can be estimated from past experience or calibrated using measured data.