Drier than average winter–spring

A positive IOD often results in less rainfall than average over parts of Australia. The map below shows rainfall during positive IOD years is generally below the long-term average (decile 3 or lower, indicated by the red shading) across central and southern parts of the country. In no part of the country is there a tendency towards above-average rainfall (decile 8 or higher, indicated by the blue shading).

Positive IOD June–November rainfall deciles composite map

Warmer than average winter–spring in the south

A positive IOD often results in warmer than average temperatures for parts of Australia. The maps below show the typical maximum and minimum temperature impacts during a positive IOD. Average maximum temperatures are generally warmer than normal (decile 8 or higher, indicated by the yellow–orange shading) over large parts of Western Australia, South Australia, New South Wales and Victoria. Average minimum temperatures are typically warmer than normal in southwest Western Australia but cooler than normal in parts of the north.

Positive IOD June–November maximum temperature deciles composite map Positive IOD June–November minimum temperature deciles composite map

About the maps

The maps above are composites of the moderate to strong positive or negative Indian Ocean Dipole event years, since 1960. They provide guidance on the typical conditions during a moderate to strong event. For each of these event years, the deciles for the winter–spring and summer period are calculated against all years since data was available to the relevant latest month. These deciles are then averaged for each point in Australia, and the result mapped.

Rainfall and temperature in positive or negative Indian Ocean Dipole event years does not follow an identical pattern to the maps above. These maps show average patterns. In reality, each event will be slightly different and it is always possible for areas of below-average rainfall to occur during a negative Indian Ocean Dipole event, or above-average rainfall during positive Indian Ocean Dipole event.