Likelihood-based approaches to flood frequency estimation

The aim of a flood frequency analysis is to make inferences about the frequency with which extreme river flows occur at a location of interest, hereafter referred to as the target site. It is a common practice to use information from several locations for this purpose, especially when flood data are limited or non-existent at the target site. A crucial issue is then how information from different locations is combined. Should data from the target site be predominant or should the estimated flood characteristics be some sort of average of those at the locations used? How should information on the variability in flood characteristics between different locations be used? How best can information on important hydrological variables be incorporated? This article examines these issues. Two likelihood-based approaches, a regression model and an empirical Bayes analysis, are described and related to the widely used region-of-influence approach. In the discussion a regression model incorporating random site effects is proposed. (C) 2004 Elsevier B.V. All rights reserved.