This is a three-way relationship that defines the statistical distribution of rainfalls expected to occur at a particular location. It is derived from statistical analysis of rainfall pluviometers or automatic raingauges, which record rainfalls occurring over different time durations.

The term 'I-D-F' is used more commonly outside of Australia. Forms of I-F-D relationships are shown below.

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They are often presented with logarithmic scales for intensities and special scales for durations.

In 2013, the Bureau of Meteorology (BOM) issued design rainfall data in the form of depths instead of intensities, producing a different type of chart that plotted depths for various durations and annual exceedance probabilities (AEPs).  These were updated in November 2016 and in early 2017, I-F-D tables and charts became available for both intensities or depths, as shown below:

This 2016 data can be entered into DRAINS by a two-stage process, first downloading files containing depths and temporal patterns and then inputting these into DRAINS.

The older 1987 IFD relationships can be calculated for any location in Australia using:

1. the BOM website at http://www.bom.gov.au/water/designRainfalls/ifd/index.shtml, using the latitude and longitude of the required location, in the process described here;
2. nine factors corresponding to the required location, taken from maps in Volume 2 of Australian Rainfall and Runoff (1987).  DRAINS can perform the necessary calculations using data entered in the IFD Data property sheet, I-F-D data was made available;
   
3. a table or chart of IFD data from the Bureau of Meteorology or the local council that administers the place where intensities are required.