The reliability of the extended Time Compression Approximation (TCA), commonly adopted in watershed models in order to represent the infiltration associated with erratic rainfalls, is investigated. This approximation is considered as a component of an adaptive real-time flood forecasting model. The forecasted flows are compared with those obtained replacing the extended TCA with the Complex Storm Point Infiltration Model (CSPIM) recently proposed by Smith et al. (1993). The discharge forecasted through the infiltration component based on the numerical solution of Richards' equation is used as a bench mark. The models were applied to situations representative of real areas in Central Italy. The CSPIM based watershed model was found to provide excellent results. The TCA based model, in spite of the adaptive component, yielded poor results for various rainfall patterns. However, it seems to be a reasonable approximation when a uniform rainfall spatial distribution is involved.

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