Uniqueness of the relationship between the return periods of the annual maximum series (AMS) and the partial duration series (PDS) are evaluated in light of the actual data. Rainfall intensities with durations of 15, 30, 60, and 360 minutes are calculated for seven stations representing a variety of climatic conditions (humid, cold, desert, and hot desert), and the corresponding AMS and PDS values are considered. PDS values are evaluated in view of annual exceedance series (AES), up to the minimum one observation (MOO). The two-parameter gamma distribution is found to be the most suitable to provide various return periods for the calculated rainfall intensities. A comparison of the results suggests that a unique relationship does not exist between return periods of AMS and PDS. Indeed, length ratio (ratio of record length of PDS series to that of AMS) should be considered as an additional independent variable. Therefore, any further attempts to extend the uniqueness of the relationship between AMS and PDS for the computation of hydrological variables such as rainfall depth are shown to be inappropriate. Finally, it is concluded that any relationship between AMS and PDS return periods is actually a function of rainfall duration as well as station location.

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