A variety of models and formulas exist to represent the precipitation-flow transformation. In the recent years, simple formulas describing the long-term hydrological balance have received a lot of interest; the most widely discussed being the Turc-Mezentsev (Turc, 1954; Mezentsev, 1955) and the Tixeront-Fu (Tixeront, 1964; Fu, 1981) formulas.