HARC was commissioned in 2023 by Queensland Reconstruction Authority (QRA) to review and revise design rainfall intensity data (IFD) for South East Queensland, Wide Bay and Burnett Regions, and parts of the Darling Downs region. The study region covered 11 local government areas with a total area of 77,215 km², including the entirety of the Borumba Dam catchment and Mary River basin. QRA managed the project, with joint funding provided by the Australian and Queensland governments. The stimulus for the project arose over concerns that the 2016 IFD grids produced by the Bureau of Meteorology were based on data up to 2012 and several very significant rainfall events have occurred after 2012, and that the derivation of the 2016 IFD grids excluded analysis of a large number of rainfall gauges operated by local government and dam owners.
HARC produced updated IFD data grids across the entire region, for 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 grids 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 (2004) draft of the Climate Change Considerations Chapter of ARR.
