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Precipitation Intensity - IDF Curves

About IDF curves (statistics)

IDF statistics characterize maximum rainfall events and calculate relations between intensities, duration and frequency of rain events in a stationary status. Environment Canada supplies this information for every station equipped with a tipping bucket rain gauge. These statistics provide also the probability of different rain event intensities for different durations (5, 10, 15, 30 minutes and 1, 2, 6, 12, 24 hours) in a given place. IDF curves are produced from these statistics and an each curve represents a certain frequency of occurrence or a certain return period expressed in terms of years.

Usefulness

Summer torrential rains and floods that may results from these rain events constitute one of the most striking illustrations of what is an extreme event. Risk evaluation and mitigation necessitate statistical information in order to plan appropriate infrastructures related to sewage, dikes... in order to protect with efficiency the population and the goods.

Users

Municipalities, governments, engineers, insurance and risk management companies... are all possible users of IDF curves.

Methodology

Past and current IDF statistics computed by the Meteorological Service of Canada (MSC) uses the Gumbel distribution of Fischer-Tippett type I to describe the frequency of extreme rains. This law of distribution is also used by most of the official meteorological services (OMM, 1981). The fit method of moments is used to adapt distribution Gumbel to extreme rains (Hogg and al., 1985) and to this date is part of the classical analysis approach.

The law of Gumbel has the advantage to be very known by the engineer's community which uses it within the works on the reliability of infrastructures.

Availability of IDF curves

These files can be downloaded for each province, territory or for all of Canada by using this link: IDF Files.