The maps below are composites, or the average impact, of moderate to strong positive Indian Ocean Dipole (IOD) years since 1960. Moderate to strong years are years where there were 2 consecutive, 3-month averages of the IOD index more than 1.5 standard deviations above average, over all years between 1960 and 2023. The years since 1960 were analysed as sea surface temperatures were less reliable prior to this period, due to the reduced availability of satellite observations.
Using this criterion there are 11 moderate to strong positive IOD years between 1960 and 2023. They are: 1961, 1963, 1967, 1972, 1982, 1994, 1997, 2006, 2008, 2012, 2019.
These years were selected because they provide the clearest historical picture of their impact on our climate patterns. However, each positive IOD year is different, and many positive IOD years are weaker in strength. The composite maps are therefore only a guide to the potential influence of a positive IOD. It should not be expected that the climate pattens in any given positive IOD year will match those shown. It is always possible for some regions to receive above average rainfall during a positive IOD year. For each selected year, the deciles for each winter–spring period were calculated against all years since data was available, up to the relevant latest month in 2023. These deciles were then averaged for each point in Australia, and the result mapped.
Historically, a positive IOD has often resulted in less rainfall than average over parts of Australia. The map below shows rainfall during positive IOD years has typically been below average (decile 3 or lower, indicated by the red shading) across central and southern parts of the country.
The temperature deciles maps show the average pattern of maximum (Figure 2) and minimum (Figure 3) temperature during moderate to strong positive IOD events in the past. Historically, a positive IOD has often resulted in warmer than average maximum temperatures (decile 8 or higher, indicated by the yellow–orange shading) over large parts of Western Australia, South Australia, New South Wales and Victoria. Minimum temperatures have typically being warmer than average (decile 8 or higher) in the south-west of Western Australia, while being below average (decile 3 or lower) in parts of the north.
