A methodology is developed to predict available water supply levels for a region. Using the technique of system identification the relationship between precipitation and runoff is mathematically modeled by a non-linear, time-variant system of partial differential equations derived from a kinematic wave formulation. The theoretical model is adapted to a particular watershed using parameter identification techniques. The development mathematical model is utilized to generate runoff data from long precipitation data. The methodology is particularly applicable to regions of long term precipitation data but limited streamflow runoff data. Predictions of available regional water supply can be made through the use of confidence interval estimations. (Author)