1:45pm 25/08/2026 to 1:45pm 27/08/2026
Maximum observed rainfall by duration, estimated return period and AEP
Duration
Rainfall
Start
End
Years
AEP
15m
5.6 mm
4:15am 27/08/2026
4:30am 27/08/2026
1 in 1.2 years
86.87 %
30m
5.8 mm
4:00am 27/08/2026
4:30am 27/08/2026
1 in 1.0 years
96.78 %
45m
7.6 mm
4:15am 27/08/2026
5:00am 27/08/2026
1 in 1.1 years
92.61 %
60m
8.6 mm
4:15am 27/08/2026
5:15am 27/08/2026
1 in 1.1 years
91.65 %
90m
9.4 mm
4:00am 27/08/2026
5:30am 27/08/2026
1 in 1.1 years
94.78 %
120m
9.8 mm
3:45am 27/08/2026
5:45am 27/08/2026
1 in 1.0 years
96.47 %
3h
10.6 mm
2:45am 27/08/2026
5:45am 27/08/2026
1 in 1.0 years
98.17 %
4h
13.0 mm
4:15am 27/08/2026
8:45am 27/08/2026
1 in 1.0 years
96.62 %
6h
16.8 mm
4:15am 27/08/2026
10:15am 27/08/2026
1 in 1.1 years
90.74 %
9h
22.6 mm
4:00am 27/08/2026
1:00pm 27/08/2026
1 in 1.2 years
80.72 %
12h
24.4 mm
1:30am 27/08/2026
1:30pm 27/08/2026
1 in 1.2 years
82.87 %
18h
26.6 mm
7:30pm 26/08/2026
1:30pm 27/08/2026
1 in 1.2 years
86.63 %
24h
26.6 mm
1:30pm 26/08/2026
1:30pm 27/08/2026
1 in 1.1 years
90.35 %
30h
26.6 mm
7:30am 26/08/2026
1:30pm 27/08/2026
1 in 1.1 years
92.93 %
36h
26.6 mm
1:30am 26/08/2026
1:30pm 27/08/2026
1 in 1.1 years
95.02 %
Note: A '1 in 1.0 years' estimate means that it is almost certain to occur at least once in a year, and could occur much more than once per year on average. For smaller values like this the Annual Recurrance Interval (ARI) may be of more relevance, but it is complex to calculate for common events.
IFD describes how rainfall intensity relates to how long it lasts and how often it happens. It is the basis for design rainfall used in engineering and flood studies.
- Duration: the length of the rainfall burst, from a few minutes to several days.
- AEP (Annual Exceedance Probability): the chance, in any one year, of a rainfall of that depth or greater. A 1% AEP event has a 1 in 100 chance each year - what is often loosely called a '1 in 100 year' event.
- The curves show design rainfall depths for a range of AEPs. The observed maximums for this location and period are plotted against them so you can see how rare the event was.
Design rainfall data is sourced from the Bureau of Meteorology.

