Probabilistic envelope curves for extreme rainfall events

This study extends the concept of the regional envelope curve (REC) of flood flows to extreme rainstorm events by introducing the Depth-Duration Envelope Curves (DDEC). DDEC are defined as regional upper bounds on observed rainfall maxima for several rainfall durations. The study adapts the probabilistic interpretation recently proposed for REC, which enables one to estimate the recurrence interval T of the curve, to DDEC. The study also assesses the suitability of DDEC for estimating the T-year rainfall event associated with a given duration and large T values. We illustrate an application of DDEC to annual maximum series of rainfall depth with duration spanning from 15 min to 24 h collected at 208 raingauges located in northern-central Italy. The accuracy of rainfall quantiles retrieved for ungauged sites from DDEC is assessed through a comparison with a Regional Depth-Duration-Frequency Equation that was recently proposed for the same study area.