Short-duration rainfall intensity-duration-frequency (IDF)

An IDF curve or graph is produced from an extreme value statistical analysis of at least 10 years of rate-of-rainfall observations. The basic IDF information is provided in files containing the IDF tables and graphs. It includes the frequency of extreme rainfall rates and amounts corresponding to the following durations: 5, 10, 15, 30 and 60 minutes, and 2, 6, 12, and 24 hours. Return periods are used as the measure of frequency of occurrence and are expressed in years. Estimates of the rates and amounts for the durations noted above and their confidence intervals for the rates are provided for return periods of 2, 5, 10, 25, 50 and 100 years.