2003 – The Impact of the Revision of Probable Maximum Precipitation Estimates in the GTSM Region of Australia

J.H. Green, D.J. Walland, N. Nandakumar

The Bureau of Meteorology has recently revised the Probable Maximum Precipitation (PMP) estimates for the Generalised Tropical Storm Method (GTSM) region of Australia. The revision process has involved the application of the more technically rigorous Generalised Southeast Australia Method (GSAM) that was previously developed for the southern part of Australia to a much larger data set of severe tropical storms. This has generally lead to an increase in the total GTSM PMP depths with a resultant increase in the Probable Maximum Precipitation Design Flood (PMPDF) and the Probable Maximum Flood (PMF).

In addition, the revision process has produced significant modifications to the temporal and spatial patterns adopted when applying the PMP depths to a dam’s catchment and these changes have also generally lead to increases in the resultant floods.

This paper discusses the rationale behind the increases in PMP depths and changes in the associated temporal and spatial patterns and presents the justification for the adoption of these more scientifically defensible estimates.

The application of the revised PMP estimates to the Keepit Dam catchment in northern NSW is presented and a comparison between the PMPDF and PMF estimates based on the original GTSM and the revised GTSM (GTSMR) made for this specific case study.

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