An El Niño event often results in less rainfall than average over much of eastern Australia.
The 14 strongest El Niño events which had the 'classic' autumn to autumn pattern of evolution and decay, started in 1905, 1914, 1940, 1941, 1946, 1965, 1972, 1977,1982, 1991, 1994, 1997, 2002 and 2015.
The map below shows 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 northeastern 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. Small coastal areas in southern Western Australia are affected, as is the north of the Northern Territory.
It should be remembered that 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 is little or no consistent El Niño effect for this time of year across central and southern parts of the Northern Territory and adjacent parts of Western Australia. In no parts of the country is there a consistent tendency towards above average (decile 8 or higher) rainfall in El Niño years.
It should not be expected that winter–spring rainfall in any given El Niño year will follow the pattern of Figure 1, nor should it be expected that 'above average' rainfalls will not occur during an El Niño year.
El Niño years tend to see warmer-than-average temperatures across most of southern Australia, particularly in the spring and summer months. Although maximum temperatures are generally warmer than average, decreased cloud cover often leads to cooler-than-average night-time temperatures during winter–spring and a longer frost season.
Generally, El Niño's impact on Australian rainfall diminishes from November onwards, so that by summer (Figure 2), the El Niño-induced tendency towards drier than average conditions has almost entirely broken down across the east and south of the country. The most significant exceptions are the east of Cape York and northwest Tasmania, both of which have a moderate drier response. Scattered areas along the Queensland/New South Wales border show a weak tendency for wetter conditions. There is a somewhat stronger and more widespread tendency for wetter than average conditions over the southeast of Western Australia.
It should not be expected that summer rainfall in any given El Niño event will follow the pattern of Figure 2. Furthermore, as the influence of El Niño often decreases during the season, it is possible for there to be a marked contrast between the rainfall patterns of early and late summer. That is, hot and dry conditions in the first part of the season can be replaced by milder, wetter weather in the second part.
El Niño summers tend to be warmer across south eastern Australia with hotter daily temperature extremes but fewer long warm spells. Further north, El Niño is associated with both an increase in individual extreme hot days and multi-day warm spells.
The maps above are composites of the moderate to strong La Niña or El Niño event years. They provide guidance on the typical conditions during a moderate to strong event. For each of these event years, the deciles for the winter–spring and summer period are calculated against all years since data was available to the relevant latest month. These deciles are then averaged for each point in Australia, and the result mapped. Rainfall has data available from 1900, and temperature has data available from 1910.
Rainfall and temperature in La Niña or El Niño years does 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, or above-average rainfall during El Niño.