Annual floods and the partial‐duration flood series

Flood data are ordinarily listed either in annual‐flood series or in a partial‐duration series. If the expectancy of a flood in the duration series ϵ is known, then the probability of that flood being an annual flood is shown to be e^−ϵ. From this relationship it is possible to transform recurrence intervals in the partial duration series to those in the annual‐flood series. It is shown that for equivalent floods, the recurrence intervals in the partial‐duration series are smaller than in the annual‐flood series, but that the difference becomes inconsequential for floods greater than about five‐year recurrence interval.