Modeling is a powerful tool that allows the reproduction of complex ecosystems involving numerous interactions between the components of the system. In the field of agricultural hydraulics, data on rainfall and runoff constitute the raw material on which the calculations of the various hydrotechnical works are based. The lack of data and their qualities make modeling an indispensable means; it allows to complete the historical information and reproduces as faithfully as possible the observed series while bringing new information concerning their long-term behavior.