A formal approach to hydrological model conceptualization

Abstract A two-stage formal approach to hydrological model conceptualization is described. The approach requires the definition of hydrological variables in terms of states and rates, the construction of state-rate diagrams and the definition of equations for the rates based on an indepth understanding of the related hydrological processes. It is inferred that the approach can help modellers arrive at models which are conceptually more feasible for operational use and for theoretical studies. STELLA, a programme specifically designed to facilitate model conceptualization using this approach, is also briefly described. The use of the two stage formal approach with STELLA will be an excellent teaching tool for hydrological modelling.