THE PARTIAL DURATION SERIES METHOD IN REGIONAL INDEX-FLOOD MODELING

A regional index-flood method based on the partial duration series mod el is introduced. The model comprises the assumptions of a Poisson-dis tributed number of threshold exceedances and generalized Pareto (GP) d istributed peak magnitudes. The regional T-year event estimator is bas ed on a regional estimate of the GP shape parameter. Analytical approx imations of bias and variance of the regional T-year event estimator a re deduced. The performance of the regional method is evaluated in the case of regional heterogeneity and intersite dependence. For small to moderate sample sizes, the regional estimator is superior to the at-s ite estimator even in extremely heterogenous regions, the performance of the regional estimator being relatively better in regions with a ne gative shape parameter. When the record length increases, the relative performance of the regional estimator decreases, but it is still pref erable to at-site estimation in moderately heterogeneous and homogeneo us regions for large sample sizes. Modest intersite dependence has onl y a small effect on the performance of the regional index-flood estima tor.