Defining intensity-duration-frequency curves at short durations: a methodological framework

In the field of sub-hourly durations, and especially in urban hydrology, selecting the most appropriate form of the intensity-duration-frequency (IDF) curve becomes a relevant question. In this study, two different formulations of IDF curves - that are characterized by a curvature in the sub-hourly intervals and a power-law formulation for the super-hourly intervals - are proposed in order to maximize the overall information contribution in the sub-hourly and the super-hourly domains. The proposed formulations are compared with two well-known IDF formulations, respectively characterized by a power-law and a curvature (from the power-law) formulation, calibrated only using data referring to super-hourly durations. Findings indicated that the proposed IDF curves allow to account for the different lengths of the sub-hourly and canonical data series and eventually for the different behaviour/trend of sub-hourly and super-hourly data, thus providing the best reliability indicator, at least in the investigated return period.