Robustness of Regionally Derived, Short-Duration Rainfall Depth-Duration-Frequency Estimates to the Choice of Minimum Interevent Time: Evidence across Climates, Rain Gauge Densities, and Regionalization Approaches

Abstract

The choice of minimum interevent time (MIT)—a criterion used to discern independent events from a continuous rainfall record—can affect the resulting partial duration series (PDS) and depth-duration-frequency values (DDFs). However, the mechanisms by which MIT choice affects regional DDFs—and how they are modulated by the choice of regional frequency analysis (RFA) framework—remain unclear. Here, we investigated these effects for short-duration ( ≤ 2    h ) precipitation, over a range of MITs (1 to 8 h) and average recurrence intervals (ARIs between 0.75 and 100 years), by applying two standard RFA frameworks—the station-year and the index-flood methods—to four study areas spanning diverse geoclimates and rain gauge densities. We found a robust preservation of tail-event identity for all regions: the magnitudes and ranks of the greatest exceedances that govern tail-events probabilities remain invariant to MIT. Shorter MITs increase the proportion of large exceedances in the PDS, and when combined with invariant tail behavior, produce a systematic sensitivity: MIT effects are most pronounced at low ARIs ( ≤ 2    years ), with smaller MIT values yielding larger DDFs. The index-flood method propagates station-level sensitivity to the regional scale through its index variable, whereas the station-year method attenuates it via spatial pooling. MIT choice introduces only modest variability in regional DDFs (for ARIs ≤ 25    years )—often within ± 1 % for most sites across all study regions—relative to dominant uncertainties such as sampling variability. Nonetheless, MIT is important for identifying independent events; in practice, a reasonably selected MIT combined with an appropriate RFA technique results in negligible effects on regional DDFs.