The rainfall-runoff modeling is very useful for forecasting purposes.
A good methodology for forecasting the future stream flow is a key req
uirement for designers and operators of water resources systems. A com
promise between conceptual and classical time series modeling is appli
ed to model the relationship between rainfall and runoff. The dynamic
nonlinear model is composed of a probability distribution describing t
he observation, a link function relating its mean to the so called sta
te parameters and a system of equations defining the evolution of thes
e parameters. Its Bayesian nature permits to take into account subject
ive information: making forward intervention, defining monitoring sche
mes and introducing smoothing facilities. An application using the dat
a of Fartura river's basin is reported. The assessment of the prior di
stribution is discussed and the predictive performance of the linear a
nd the non-linear models is reported.