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).
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 and Victoria. Average minimum temperatures are typically warmer than normal in southwest Western Australia but cooler than normal in parts of the north.
The maps above are composites of 9 positive IOD years since 1960. They provide guidance on the typical conditions to expect during a positive IOD. For each of the 9 years, the deciles for the winter–spring period are calculated against all years between 1900 and 2015 for the rainfall map, and 1910 and 2015 for the temperature maps. These deciles are then averaged for each point in Australia, and the result mapped. Rainfall and temperatures for any particular positive IOD years will 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 above-average rainfall and below-average temperature to still occur during a positive IOD.