The primary processing of high-resolution precipitation records (5 min and shorter) is crucial for constructing dimensionless design hyetographs and identifying design-critical precipitation scenarios for urban drainage systems. A key step in this process is separating continuous precipitation records into individual precipitation events, typically based on minimum inter-event time (MIT) and precipitation amount thresholds. This separation directly influences the subsequent analysis steps and the accuracy of the design hyetographs. Building upon this foundation, this study systematically analyses how different MIT determination methods influence the construction of dimensionless Huff hyetographs in a moderately humid continental climate. Three approaches for defining MIT were examined: a fixed MIT method (1–12 h), an autocorrelation-based method (AC), and a kernel density estimation approach (KDE). The analysis also considers the effects of minimum precipitation thresholds (P = 1, 3, and 5 mm) and precipitation duration classes (all durations and short-duration events with T≤2 h), utilising a continuous 10-year series of 5 min precipitation data. The results demonstrate that the choice of MIT substantially affects the identified precipitation events, duration, total amount, and the median Huff curve’s shape, especially for precipitation types with early and late maximum intensity. Specifically, increasing MIT values produces longer and deeper events with steeper Huff curves, while precipitation thresholds mainly filter weaker events rather than impacting peak intensities. The AC method yields results similar to larger fixed MIT values (≈6–9 h), whereas the KDE method corresponds to shorter separations (≈1–3 h). To unify the assessment of design relevance, a composite design index combining Huff curve slope and short-term peak intensities was introduced. Analysis shows that short-duration convective precipitation with an early maximum is the most critical design scenario. However, late-maximum events (events in which peak intensity occurs in the fourth quartile of storm duration, Type 4) can become equally critical when longer MIT values or autocorrelation-based separation are applied. These findings underscore the importance of a transparent and methodologically consistent definition of precipitation event separation criteria when using dimensionless hyetographs in urban drainage design.
Grubišić et al. (Mon,) studied this question.