PMP Estimates

Probable Maximum Precipitation (PMP) Estimates can be produced for any catchment in Australia. There are
3 Generalised Methods used to estimate PMP, appropriate for different locations and durations:

Generalised Short-Duration Method (GSDM)

GSDM downloadable document merges the method and data from Bulletin 53 with recently introduced amendments.

Revised Generalised Tropical Storm Method (GTSMR)

GTSMR guide to the application of the method on compact disc.

Generalised Southeast Australia Method (GSAM)

GSAM guide to the application of the method on compact disc.

For long durations, for catchments located in western Tasmania, the West Coast of Tasmania Method of Storm Transposition and Maximisation is applicable.

A PMP report provides the PMP depth, averaged over the catchment, as a function of duration, from 1 hour to a maximum of 4 days depending on the location; the spatial distribution of the rainfall over the catchment; and the temporal distribution of the rainfall during the period of the PMP storm.

What is PMP?

Probable Maximum Precipitation (PMP) is defined by the Manual for Estimation of Probable Maximum Precipitation (WMO,1986) as:

"...the greatest depth of precipitation for a given duration meteorologically possible for a given size storm area at a particular location at a particular time of the year, with no allowance made for long-term climatic trends."

Hydrologists use a PMP magnitude, plus its spatial and temporal distributions, to calculate the Probable Maximum Flood (PMF) for the catchment of a dam. The PMF is used to design the dam.

What are Generalised Methods?

Generalised Methods of estimating PMP use data from all available storms over a large region and include adjustments for moisture availability and differing topographic effects on rainfall depth. The adjusted storm data are enveloped by smoothing over a range of areas and durations. Generalised methods also provide design spatial and temporal patterns of PMP for the catchment.

Last Modified: 23 November 2006, Hydrometeorological Advisory Service.