The increased cloudiness and rainfall associated with La Niña periods typically reduces daytime temperatures and keeps nights warmer, particularly over northern and eastern Australia. In the north of Australia, the monsoon is typically enhanced, which can lead to both cooler days and nights during the summer monsoon season as the higher rainfall allows for increased evaporative cooling, and increased onshore winds provide additional cooling in the same way a sea-breeze brings relief from a hot summer day.
In contrast, during El Niño events, reduced cloudiness means daytime temperatures are typically warmer than normal, exacerbating the effect of lower than normal rainfall by increasing evaporation. Reduced cloudiness also means that nights can be cool, sometimes leading to widespread and severe frosts; Australia's lowest recorded temperature, –23.0 °C, was observed at Charlotte Pass on 29 June 1994, during the 1994–95 El Niño event.
The temperature effect of El Niño events are felt most strongly during winter and spring, while the effects of La Niña events tend to have the greatest impact between October and March. The effect of La Niña events also tends to be stronger than that for El Niño; temperatures are generally further below average during La Niña events than they are above average during El Niño events.
During La Niña increased cloudiness and rainfall can lead to cooler days.
During El Niño reduced cloudiness can lead to warmer days.
Evaporative cooling
Evaporation of surface water, such as lakes, or moisture in the soil, cools the environment surrounding it. This happens because changing a substance from a liquid phase to a gaseous phase (evaporation) requires energy. The energy required for a phase change is known as latent heat, and can be provided by absorption of solar radiation or by drawing heat energy from the air or other substances in contact with the liquid.
Temperature patterns during ENSO events
Average impacts of La Niña and El Niño events on maximum (daytime) and minimum (night-time) temperatures across Australia are shown below in composite maps combining temperature data from 12 of the strongest 'classic' events.
The maps show mean maximum and minimum temperature deciles, where blue tones indicate below-average temperatures and orange to red tones indicate above-average temperatures.
Note that the temperature patterns can vary significantly from one event to the next.
El Niño
Winter/spring daytime temperatures – above average across southern Australia
Summer daytime temperatures – slightly above average for most of eastern and northern Australia
Winter/spring minimum temperatures – above average for the southwest, below average for the northeast and parts of the east
Summer minimum temperatures – above average across southern Australia
The onset years for the 12 strongest 'classic' El Niño events used are 1914, 1940, 1941, 1946, 1965, 1972, 1977, 1982, 1991, 1994, 1997 and 2002.
La Niña
Winter/spring daytime temperatures – below average across southern Australia
Summer daytime temperatures – below average across most of northern and eastern Australia
Winter/spring minimum temperatures – above average for much of northern Australia, below average for most of the southwest
Summer minimum temperatures – below average for northern Australia, above average for parts of the southeast
The onset years for the 12 strongest 'classic' La Niña events used are 1910, 1916, 1917, 1950, 1955, 1956, 1971, 1973, 1975, 1988, 1998 and 2010.
