Mass Budget Methods

Abstract

Mass budget methods are based on the principle of conservation of mass applied to some part of the hydrological cycle. Conservation of mass, formulated as a mass budget equation, requires that, in general, for any given control volume, the inflow rate minus the outflow rate equal the rate of change of the water stored. Accordingly, evaporation can be determined as the only unknown rest term in the budget equation if all the other terms can be determined independently. Although, from the conceptual point of view, mass budget methods are by far the simplest, their application is often difficult and impractical. Therefore, they are less commonly used than aerodynamic or energy budget methods. Nevertheless, their conceptual simplicity is an appealing feature and, in certain situations, a mass budget approach can be quite appropriate. In this chapter a brief description is given of several ways in which the mass budget can be applied in practice.