QRA Specific Data Info

How do the QRA IFDs differ from previous IFDs?

The updated QRA IFDs were finalised in April 2025 and use a larger dataset than previous estimates, including data through the end of 2023. The IFDs are adjusted to a dataset midpoint of 2010 in accordance with the ARR version 4.2 rainfall factors. The methodology differs from previous IFD datasets and is described in the full report.

Background

Following the 2022 floods in South East Queensland, the Queensland Reconstruction Authority (QRA) commissioned HARC to review and revise design rainfall intensity data (IFD) for South East Queensland.

The study area covers the local government areas of:

• Brisbane City Council
• Bundaberg Regional Council
• Cherbourg Aboriginal Shire
• Fraser Coast Regional Council
• Gold Coast City Council
• Gympie Regional Council
• Ipswich City Council
• Lockyer Valley Regional Council
• Logan City Council
• Moreton Bay City Council
• Noosa Shire Council
• North Burnett Regional Council
• Redland City Council
• Scenic Rim Regional Council
• Somerset Regional Council
• South Burnett Regional Council
• Sunshine Coast Regional
• Toowoomba Regional Council
• Parts of Western Downs Regional Council

The updated IFD data includes all 24 standard rainfall burst durations between 5 minutes and 7 days and for all standard annual exceedance probabilities (AEP) between 63% and 1 in 2,000 AEP. Frequency analysis was undertaken on daily and sub-daily rainfall gauge data from 1,377 rainfall gauges and then regionalised and spatially interpolated to produce sets of design IFD grids. The updated data were corrected to allow for the progressive influence of climate change over the rainfall data period and guidance was provided with the data for practitioners to adjust the grids for projected climate change, applying the latest DCCEEW (2024) federal draft of the Climate Change Considerations Chapter of ARR.

The full report is available here and the quick guide for users is available here.