Some Comments on Regionalization in Hydrologic Studies

At the j th site, a choice must be made between y i , a statistical characteristic of the observed flows, and ŷ i , a regionalized estimate of the characteristic, for use in the model for generating synthetic flows at the j th site. The regional estimate is obtained from a regression of y on a set of basin characteristics. IfV ˆ i i/ V i i  <   2 −   ρ ′ , then ŷ i instead of y i , is used in the generating model, whereV ˆ i iand V ii are the variances of ŷ i and y i , respectively, and ρ ′ is a measure of the interstation correlations. This criterion is shown to be independent of the j th basin characteristics. The criterion is a function of the j th basin characteristics if the data at the j th site are not used in developing the regression relation. For an ungaged site, ŷ i may be obtained with variance that depends upon the basin characteristics at the j th ungaged site. (Key words: Statistics; regionalization; synthesis)