Recent work on regional flood frequency estimation has shown that accurate flood quantile estimates are possible when the underlying flood frequency distributions are identical at all sites in the region except for a scaling factor, particularly when the underlying distribution has a two‐parameter form. The class of regional probability‐weighted moment (PWM) estimators is investigated for robustness to mis‐specification of the assumed distributional form and to regional heterogeneity in moments of order higher than one. Whereas two‐parameter distributions belonging to the extreme value family perform quite well when the form of the underlying distribution is close to that of the fitted distribution, large biases can result when the distribution is misspecified. The three‐parameter generalized extreme value distribution (GEV), when fitted using the regional PWM method, has been shown to be relatively insensitive to violations of the distributional assumption, and to have low variability and bias. In this paper it is shown that regional estimation methods using the three‐parameter GEV distribution are relatively insensitive to modest regional heterogeneity in the coefficient of variation and quite insensitive to regional variation in the skew coefficient. The key determinant of the performance of the regional estimators is shown to be the regional mean coefficient of variation. For high values of the mean coefficient of variation, such as might be encountered in arid regions, an alternate PWM estimation method based on the GEV distribution that accommodates the regional heterogeneity in the higher order moments is preferred. The trade‐off between this alternate method and the approach that assumes regional homogeneity in moments higher than order one is sensitive to the record lengths.
All Science Journal Classification (ASJC) codes
- Water Science and Technology