Drying influence expands

Some positive IOD events, but not all, occur during the same year as an El Niño. The relationship between El Niño and the IOD is complicated, with the level of dependence between the two an area of active research. The map shows the mean rainfall deciles for total winter-spring rainfall for the 7 positive IOD events that coincided with El Niño since 1960.

June–November mean rainfall deciles across
Australia for seven positive IOD years and El Niño years.

The map shows that when positive IOD and El Niño coincide, the mean winter-spring rainfall is below average across nearly all of eastern and central Australia. There is a significant shift in the rainfall pattern towards dry conditions in the eastern half of the country, in line with impacts typically expected during El Niño. However, there is also a reduced rainfall signal across central Australia, which is not usually seen when El Niño occurs on its own. In no part of the country is there a consistent tendency towards above average (decile 8 or higher) rainfall.