The maps below are composites, or the average impact, of moderate to strong El Niño years. Moderate-to-strong El Niño years are where the June-to-November average Southern Oscillation Index (SOI) is greater than 1.5 standard deviations below the average over all years between 1900 and 2023.
Using this criterion there are 10 moderate to strong El Niño years between 1900 and 2023. They are: 1905, 1914, 1940, 1941, 1965, 1977, 1982, 1994, 1997 and 2015.
These years were selected because they provide the clearest historical picture of their impact on our climate patterns. However, each El Niño year is different, and many El Niño years are weaker in strength. The composite maps are therefore only a guide to the potential influence of an El Niño. It should not be expected that the climate pattens in any given El Niño year will match those shown. It is always possible for some regions to receive above average rainfall during an El Niño year.
For each selected year, the deciles for each seasonal period were calculated against all years since data were available, up to the relevant latest month in 2023. These deciles were then averaged for each point in Australia, and the result mapped. Rainfall has gridded data available from 1900, and temperature has gridded data available from 1910. This means that the temperature composite maps are for an average of 9 moderate to strong El Niño years, while rainfall has 10 years.
To illustrate the variations of rainfall and temperature, links to winter-spring and summer maps for each year are also included below.
Historically, a moderate to strong El Niño has typically resulted in less rainfall than average over much of eastern Australia.
Figure 1 shows rainfall has historically been below average (deciles 2 or 3, indicated by the red shading) for the six-month winter–spring period, across much of eastern Australia. Regions specifically affected include the north-eastern half of Tasmania, almost all of Victoria, almost all of New South Wales (excluding coastal districts), eastern and coastal parts of South Australia, and much of Queensland (excluding the south-east coast). Small coastal areas in southern and northern Western Australia are affected, as is the north of the Northern Territory.
The winter–spring period covers a lot of the dry season for northern Australia. In the dry season, zero monthly rainfall totals are quite common in some northern and central parts even in ordinary years, so it is not surprising that there typically has been little or no consistent signal from El Niño for this time of the year across central and southern parts of the Northern Territory and adjacent parts of Western Australia.
Winter–spring rainfall in moderate to strong El Niño years: 1905 1914 1940 1941 1965 1977 1982 1994 1997 2015
Historically, a moderate to strong El Niño has typically resulted in warmer-than-average temperatures across most of southern Australia, particularly in the spring and summer months. Although maximum temperatures (Figure 2) have typically being warmer than average, decreased cloud cover often leads to cooler-than-average night-time temperatures during winter–spring for parts of the south-east (Figure 3) and a longer frost season. Maximum and minimum temperatures have typically been cooler than average across much of far northern Australia.
Generally, El Niño's impact on Australian rainfall has diminished from November onwards, so that over summer the influence of El Niño on rainfall has been low, especially as the season progressed (Figure 4). The most significant exception is the east of Cape York, where there has typically been a tendency towards below average rainfall.
Summer rainfall in moderate to strong El Niño years: 1905–06 1914–15 1940–41 1941–42 1965–66 1977–78 1982–83 1994–95 1997–98 2015–16
El Niño summers have historically tended to be warmer across southern Australia, with hotter daily temperature extremes but fewer long warm spells. Further north, an increase in individual extreme hot days and multi-day warm spells has typically been observed during El Niño summers.
