A La Niña event often results in more rainfall than average from northwestern Australia to the south east.
The 13 strongest La Niña events which had the 'classic' autumn to autumn pattern of evolution and decay, started in 1910, 1916, 1917, 1938, 1950, 1955, 1956, 1971, 1973, 1975, 1988, 1998, and 2010.
The map below shows winter–spring rainfall during La Niña years is generally above average (decile 8 or higher, indicated by the blue shading) across northern and central Australia. Some of this is often from heavier rainfalls in October and November associated with an early start to the northern wet season in La Niña years.
Winter–spring rainfall is not the exact opposite of the corresponding El Niño impact. Northeast Tasmania, northern Victoria, and eastern parts of South Australia show a tendency towards wet conditions in La Niña years, similar in strength to the El Niño tendency towards dry conditions in El Niño years. For northern South Australia and northern Queensland, the La Niña response is stronger than the El Niño response.
The effect of La Niña events on winter–spring rainfall is limited for coastal areas of Victoria and New South Wales, extending almost to Fraser Island in southern Queensland. The reasons for the lack of a consistent response of winter–spring rainfall to El Niño and La Niña events for the coastal areas of New South Wales and southern Queensland are the subject of current research, but it should be noted that rainfall in these parts often arises from the lifting of on-shore 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.
La Niña years tend to see cooler than average daytime temperatures 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, regions of southern New South Wales and northern Victoria can experience less frost days.
Generally, La Niña's impact on Australian summer rainfall (Figure 2) is relatively less than the winter–spring impact. This is especially the case over Tasmania, SA, the NT and WA which have large areas of deciles 5 and 6 (shaded white). Like the winter–spring period, the impact from La Niña is more widespread and intense during summer than the corresponding impact from El Niño.
There is a contraction and weakening of the effect in western Queensland, but in the east of that state, the La Niña-induced tendency towards wetter than average conditions continues to be moderate to strong. This is significant as December to February are, on average, three of the four wettest months in this part of the country. In eastern NSW, there is an increased tendency for wet conditions in comparison with the impact during the winter-spring period. As with eastern Queensland, this is significant in northern NSW because the region experiences a natural summer rainfall maximum.
It should not be expected that summer rainfall in any given La Niña event will follow the pattern of Figure 2.
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.
The maps above are composites of 13 La Niña event years. The maps provide guidance on the typical conditions during a La Niña event. For each of these years, the deciles for the winter–spring and summer period are calculated against all years between 1900 and 2019. These deciles are then averaged for each point in Australia, and the result mapped. Rainfall for all La Niña 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 below-average rainfall to occur during a La Niña.