Campania (Kincora) - IFD

The words on this page

Design rainfall, or IFD, is short for intensity, frequency and duration. It is the rainfall depth used for sizing drains, culverts and flood models: how much rain falls in a burst of a given length, at a given chance of happening. It is worked out from decades of records, so it is a statistic rather than a forecast.

AEP is annual exceedance probability, the chance in any one year of a burst that big or bigger. A 1% AEP burst is the one people often call a 1 in 100 year event.

ARR is Australian Rainfall and Runoff, the national guide to flood estimation. Its chapter on climate change was rewritten in 2024, and that rewrite is the method used here.

SSP is shared socioeconomic pathway, one of the standard scenarios for how much greenhouse gas the world emits this century. Of the four offered here, SSP1-2.6 is the lowest, then SSP2-4.5, then SSP3-7.0, and SSP5-8.5 is the highest.

What each choice does

• None draws the Bureau's 2016 design rainfall for this location, unchanged. These are the published figures, and they do not allow for future climate change.
• Present day raises those curves for the warming that has already happened, compared with the older climate the 2016 figures represent.
• Projection raises them for a year you choose, under a pathway you choose.

The year is the year you are designing for, usually near the end of the working life of whatever is being built. A later year normally means a bigger increase, except under the lowest pathway, where the increase stops growing after about 2070. A higher pathway always gives a bigger increase than a lower one in the same year. The increase is larger for short sharp bursts than for rain lasting a day or more.

Which one to pick

• Leave it on none if you want the figures the Bureau publishes, which is where most Australian design work still starts.
• Choose present day to see how far the numbers have already moved.
• Choose a projection if you are sizing something that has to last. Use the year nearest the end of its life, and the pathway your council or state guidance asks for. If nobody has told you which pathway to use, comparing the lowest and the highest shows you the range you are dealing with.

The adjusted figures on this page are worked out by us from the Bureau's values and the published national factors. They are not Bureau published design rainfall, and they do not replace the guidance that applies where you are.

Where the figures come from

• Bureau of Meteorology design rainfall, the source of the 2016 curves.
• Bureau of Meteorology design rainfall questions and answers, which says the 2016 figures do not include the effects of future climate change and points readers at the Australian Rainfall and Runoff climate change chapter.
• Australian Rainfall and Runoff, version 4.2. Book 1 chapter 6 carries the climate change method used here. It is a large download.
• The Australian Rainfall and Runoff data hub, which publishes the climate change factors, and its changelog, which dates the 2024 v1.01 factors to 11 September 2024.
• Design rainfall climate change considerations, an addendum published in June 2025, which is where the present day warming figure comes from.
• The data hub's about page states that its data is © Commonwealth of Australia (Geoscience Australia), published under CC BY 4.0.