by Iraphne Childs

This summer we may be spared a repeat of last summer’s horrendous bushfires, but according to the Bureau of Meteorology (BOM) it looks like there is a high probability of more cyclones and flooding due to a La Niña episode.

The Walker circulation in a La Niña year; (BOM 2020)

The El Niño-Southern Oscillation (ENSO) cycle is the major influence on annual climate variability for most of Australia. El Niño in Spanish means The Little Boy and La Niña means The Little Girl. El Niño was first recognised by fishermen off the coast of South America in the 1800s with the appearance of unusually warm water in the eastern Pacific Ocean around December. Fishing in this region is best during La Niña years when cold upwelling ocean water brings rich nutrients off the coast. ENSO has been studied and monitored extensively by climate scientists throughout the 20^th century and continues to be closely monitored today in research centres in Australia and around the world.

BOM (2016)

As the BOM explains, the transition between La Niña, El Niño and neutral conditions (neither El Niño nor La Niña) is governed by interactions between the atmosphere and ocean circulation. La Niña occurs when equatorial trade winds become stronger, changing ocean surface currents and drawing cooler deep water to the surface. This results in a cooling of the central and eastern tropical Pacific Ocean where air descending over the cooler waters results in that region being less favourable for cloud and rain. Conversely, in the western Pacific Ocean and to the north of Australia stronger trade winds help to increase warm surface waters resulting in more favourable conditions for rising air, cloud development and rainfall. A La Niña year typically brings increased rainfall across much of Australia, cooler daytime and warmer overnight temperatures, more tropical cyclones and earlier monsoon onset. The air rising in the west and descending in the east enhances the Walker atmospheric circulation  which can result in changes to the climate experienced across the globe.

Cyclones can affect Queensland in the summer months during all phases of the ENSO cycle -  for example cyclones Oswald in 2013 (a neutral ENSO year), Marcia in 2015 (an El Nino year) and Debbie in 2017 (a weak La Niña year).

The 2010–2011 La Niña was one of the strongest on record (BOM 2020). In February 2011 much of Queensland experienced the effects of cyclone Yasi, one of the biggest storms in Queensland's history. This storm passed between Cairns and Townsville, eventually crossing the coast at Mission Beach. I volunteered with Red Cross and was deployed over several weeks in February and March 2011 to evacuation and recovery centres in Mission Beach, Tully, and Ingham.

In both natural and human environments biodiversity, economic, social and infrastructure recovery following the devastating damage from cyclones and flood can take years. Communities, however, display amazing resilience.

Here is are some example that I witnessed in 2011.

Main street, Ingham, March 2011

Rainforest near Mission Beach, February 2011      

Ingham banana farmers, having received timely warnings from BOM prior to Yasi’s onslaught, pre-empted total damage to their crops by braking off tall banana plants down to the base so that the winds would not rip them out of the ground, allowing the short young suckers to grow again after the storm. In and around Mission Beach and Tully, cassowaries displaced from the damaged rainforest were wandering along roads searching for food in bare sugarcane fields. Local wildlife organisations and townsfolk saved many birds from starvation by placing fruit and food packages at vantage points around town for the cassowaries.  If predictions of the La Niña weather this summer prove to be correct, no doubt there will be more stories to be told of local preparation, adaptation, and resilience. Photography courtesy of Iraphne Childs.

References

ABC News (2020) BOM declares a La Niña, signalling wet spring and summer likely for northern, eastern Australia https://www.abc.net.au/news/2020-09-29

Bureau of Meteorology (2016) What is La Niña and how does it impact Australia?

http://www.bom.gov.au/climate/updates/articles/a020.shtml

Bureau of Meteorology (2020) La Niña WATCH: what it means for 2020 17 July 2020

http://media.bom.gov.au/social/blog/2395/la-nia-watch-what-it-means-for-2020/

NOAA (2020) What are El Niño and La Niña? https://oceanservice.noaa.gov/facts/ninonina.html

BOM (2020) Record high Southern Oscillation Index (SOI) values  http://www.bom.gov.au/climate/enso/history/ln-2010-12/SOI-records.shtml