Gamma autoregressive model for annual streamflow verification and validation

Gamma Autoregressive model of order one [GAR(1)] is used for modelling the annual streamflow data of six different rivers selected from a few hydrologic regions over the globe. The bias corrections suggested by Fernandez and Salas [1] have been made use of. The model parameters are estimated using the method of moments. The validation statistics were: minimum, maximum flows, min./max. ratio, Hurst ratio, drought characteristics namely, drought duration and deficit sum. The results of verification as well as validation have been presented for all the six rivers. Four out of the six cases analyzed performed well at both the verification and validation stages, though the moments and correlations were well reproduced for all the six cases. The drought durations in general, were poorly preserved compared to deficit sum. Especially durations of severe historical droughts were very much underestimated like in the case of classical Box-Jenkins models.