Focus Areas E2- Oceanography

What is La Niña?

Like the term ‘El Niño’ which is perhaps more familiar to us, the term ‘La Niña’ refers to a large scale pattern of weather that arises from linked changes in the ocean and atmosphere. Weather events associated with a La Niña’ are especially observed in the region around the Pacific Ocean but are also of some significance in the Indian Ocean and other parts of the world.

We can define the term ‘La Niña’’ in simple terms as a broad pattern of weather events that is typically observed when sea surface temperatures of the central to eastern Pacific Ocean  fall below normal for a significant period of time.

During La Niña episodes, it is often the case that Australia (particularly the northern and eastern parts) experiences wetter than normal conditions and a higher probability of flooding rains. In contrast to the situation in Australia, countries on the eastern side of the Pacific Ocean such as Ecuador, Peru and USA, tend to have dryer than normal conditions and a higher probability of drought during a ‘La Niña’ episode.

‘La Niña’ is a natural phenomenon that has been a part of the climate of the Pacific Basin for thousands of years. There is nothing exotic about it, nor should it be regarded as just another name to describe wetter than normal conditions in eastern and northern Australia. Unfortunately while La Niña conditions recur quite often over the course of the decades they are not regular or periodic in their occurrence so predicting a La Niña episode a year or so in advance has very low probability of success at  the present time.  It is only in the last few decades that weather scientists have begun to fully investigate La Niña and El Niño. As their knowledge and understanding increases, we can expect that in future decades it might be possible to forecast La Niña episodes and their impacts, with greater accuracy.

The opposite trend in the weather patterns known as ‘El Niño’ which is observed at times in the Pacific Basin, occurs when the sea surface temperatures of the central to eastern Pacific Ocean fall below the normal for many months. During a strong ‘El Niño’ episode, Eastern Australia tends to receive lower than average rainfall while Peru tends to be wetter than usual. (See El Niño El Niño and Drought for more detail).

‘La Niña’ is a Spanish term meaning ‘the girl-child’ whereas ‘El Niño’ means ‘the boy-child’, a reference to the Christ child.  Originally, the term ‘El Niño’ was used by Peruvian fisherman to describe a warm ocean current which they sometimes experience around Christmas time off the South American coast and which is associated with poor fish catches and reduced  livelihoods. During a La Niña’ episode, the opposite conditions with cool ocean currents and better fish catches are usual along the Peruvian coast.

Figure 1:  The kind of weather conditions we sometimes experience during a sustained La Nina episode.
(Source: Shane Geerin, NSW State Emergency Service)

Students learn about El Niño and La Niña
Students learn to identify features of El Niño and La Niña