The maps below are composites, or the average impact, of moderate to strong La Niña years. Moderate-to-strong La Niña years are where the June-to-November average Southern Oscillation Index (SOI) is greater than 1.5 standard deviations above the average over all years between 1900 and 2023.
Using this criterion there are 9 moderate to strong La Niña years between 1900 and 2023. They are: 1910, 1917, 1950, 1955, 1973, 1975, 1988, 2010 and 2022.
These years were selected because they provide the clearest historical picture of their impact on our climate patterns. However, each La Niña year is different, and many La Niña years are weaker in strength. The composite maps are therefore only a guide to the potential influence of an La Niña. It should not be expected that the climate pattens in any given La Niña year will match those shown. It is always possible for some regions to receive below average rainfall during a La Niña year. However, the historical patterns of above average rainfall over parts of Australia that are associated with La Niña have tended to be more consistent than climate patterns associated with El Niño.
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.
To illustrate the variations of rainfall and temperature between moderate to strong La Niña years, links to winter-spring and summer maps for each year are also included below.
Historically, a moderate to strong La Niña has typically resulted in more rainfall than average across much of central and eastern Australia.
Figure 1 shows rainfall has historically been above average (decile 8 or higher, indicated by the blue shading) for the six-month winter–spring period across northern and central Australia. Some heavier rainfall in October and November has been associated with a tendency towards an early start to the northern wet season in La Niña years.
Winter–spring rainfall has not been the exact opposite of the corresponding El Niño pattern. The strength of El Niño and La Niña patterns has generally matched over the east, but the strength of the La Niña pattern has been stronger further west and north.
The effect of La Niña on winter–spring rainfall is limited for coastal areas of Victoria and New South Wales, extending to K'gari (formerly Fraser Island) in southern Queensland. The reasons for the inconsistent response of winter–spring rainfall to El Niño and La Niña for the coastal areas of New South Wales and southern Queensland are the subject of current research. Rainfall in these parts often arises from the lifting of onshore air streams as they flow over the Great Dividing Range. A lot of the month to month and year to year rainfall variability from these airstreams seems to be due to the chaotic nature of the mid-latitude weather systems, which form a major feature of the weather and climate patterns of southern and central Australia.
Winter–spring rainfall in moderate to strong La Niña years: 1910 1917 1950 1955 1973 1975 1988 2010 2022
Historically, La Niña has tended to see cooler than average maximum temperatures (Figure 2) across most of mainland Australia south of the tropics, particularly during the second half of the year. Due to increased cloud cover and hence warmer nights (Figure 3), regions of southern New South Wales and northern Victoria have experienced fewer frost days.
Generally, La Niña's influence on Australian summer rainfall (Figure 4) has been less than its influence during winter–spring. This has especially been the case over Tasmania, South Australia, and Western Australia, which have historically observed large areas of close to average rainfall (deciles 5 and 6, shaded white).
The continued association with above average rainfall across much of the north and east in summer is significant because these regions experience a natural summer rainfall maximum.
Summer rainfall in moderate to strong La Niña years: 1910–11 1917–18 1950–51 1955–56 1973–74 1975–76 1988–89 2010–11 2022–23
In the warmer half of the year, southern coastal locations such as Adelaide and Melbourne experience fewer individual daily heat extremes during Niña years but an increased frequency of prolonged warm spells.
