Wet Wet Wet: La Niña is all around me

La Niña: the tiny bit of Spanish everyone’s picked up from the past two summers. While translating to “the girl” a more apt translation would be “the rain”, especially given most of the country has been soaked by persistent, heavy rainfalls for the last few months. 

With the soil saturated and water catchments full to the brim, these unprecedented downpours had nowhere to go, causing devastating floods to Northern NSW and Southeast Queensland, while Sydney was also heavily impacted. The question now being asked, what’s bringing all this rain? The answer, a climate phenomenon known as the El Niño–Southern Oscillation (ENSO). This is the distribution of warm and cool water across the equatorial Pacific Ocean thanks to stronger than normal or weaker than normal easterly trade winds. 

Normally we see easterly trade winds blowing from east to west (towards Australia) either side of the equator. If these winds become stronger than normal, we see cool water upwelled from deep across the central and eastern Pacific Ocean while warm water piles up around Northern Australia. This is known as La Niña. The warm water transfers energy into the atmosphere bringing increased rainfall and storm activity through our summer and autumn.

The opposite to this is El Niño, when the easterly trade winds weaken and even reverse in direction, blowing from west to east, piling up warm water in the central and eastern Pacific Ocean. Around Australia we see cooler water developing and suppressed rainfall. There is also the neutral phase of ENSO which sees steady easterly trade-winds blowing across the Pacific and about normal rainfall falling across the country.

The past two summers have seen back-to-back La Niña events, known as a double-dip. Before the first La Niña summer (2020/21), the soil moisture levels across most of the country and especially the East Coast were at record lows, but this was rectified before becoming oversaturated during the summer of 2021/22 leading to widespread flooding events. One compounding factor to La Niña is that we also see warm water building up north-west of the country and around Indonesia, providing moisture for rainfall which is dragged southeast across the country through our winter and spring. A double whammy of factors very much bringing us out of drought.

There’s no predictable pattern to the ENSO cycle but the drier El Niño years are more common than La Niña years, with double-dip La Niña years even less frequent. There’s a small chance we could see a third La Niña next summer. The last time this occurred was in the 1970’s, bringing incredibly destructive storms with it. 

In regard to climate change, a warmer atmosphere can hold more moisture. With the oceans also warming, there’s more energy available to be transferred into the atmosphere, resulting in stronger, more volatile storm/rain events. From a surf perspective, La Niña is great as it provides an increase in easterly swells with generally more favourable winds and warmer water. El Niño is the opposite with windy days from the north-east, weaker swells and cold water upwelled by the cross-shore winds.

Looking at the months ahead, we’ll continue to fall under the influence of La Niña, bringing a wetter and cooler than normal autumn and winter. Then, how next summer pans out all depends on if we see a third La Niña. While great for bushfire recovery, I think everyone wouldn’t mind a 2022/23 summer with a bit more sunshine than we’ve just had.