Australia's big wet: La Niña explained

Parliament house flag post

Australia's big wet: La Niña explained

Posted 29/03/2012 by Anita Talberg

The Bureau of Meteorology, the CSIRO, and the World Meteorological Organisation have each released a review of Australian and world climate in 2011. According to these three sources, 2011 in Australia was generally cooler than recent years...but warm for a La Niña year. It was also a wet year for Australia...but then, that’s normal for a La Niña year. So what is La Niña? How do we understand climate change and variability in the context of a La Niña event?

La Niña in simple terms
Globally and regionally, high or low pressure systems, cold or hot fronts and strong winds coincide and interact to influence weather and climate. One domino in this chain reaction of events is the Southern Oscillation. If the Southern Oscillation is ‘swinging’ strongly one way or the other, an El Niño or La Niña event results. In between, there are neutral periods.

The Southern Oscillation plays out in the South Pacific Ocean, the space between Darwin and the Peruvian coast (going through Tahiti). In neutral periods, the ocean surface temperature around Darwin is about 28˚C, and near Peru it’s around 20˚C. In very simplistic terms, ignoring all other factors (such as trade winds and zonal air circulation patterns) an El Niño or La Niña event occurs when the ocean surface temperature difference between the northeast Australian coast and South American coast is disrupted. This happens for a host of reasons (occurring both above and below the ocean surface), some of which are not fully understood.

An El Niño event occurs when the Australian waters become relatively cooler and the South American waters relatively warmer. High atmospheric pressure tends to result over cold water, just as the pressure is generally low over warm water. As a result of these pressure differentials, during El Niño conditions the Australian climate is generally sunny,dry and warmer than usual, especially between June and November. Of course, the effects are not uniform across the continent, but overall there are drier conditions and fewer clouds, leading to an increased likelihood of bushfires. However, because of reduced cloud cover, at night the air cools more quickly, meaning that warmer-than-average days end in cooler-than-average nights.

A La Niña event is the opposite of an El Niño. Warmer waters off the coast of northeastern Australia favour lower atmospheric pressure. The greater evaporation from the warmer water brings more clouds and rain, and generally cooler conditions. This means increased chance of flooding, especially between October and March.

El Niño and La Niña periods can last anywhere from a few months to a couple of years, and repeat at irregular intervals. The graph below from the US National Oceanic and Atmospheric Administration shows the occurrences of El Niño and La Niña periods since 1950.


The year 2011 began partway through one of the strongest La Niña events on record, which lasted until April/May. A second La Niña period began shortly afterwards, in August/September 2011.


Australian temperatures and rainfall in 2011
La Niña doesn't just affect Australia. It has major ramifications over a large area and, as a result, global average temperatures in 2011 were lower than in 2010. However, they were the warmest temperatures ever recorded under La Niña conditions. While much of Australia was colder than usual, Europe, North Asia and the Americas were generally warm, although there were none of the record-like heatwaves experienced in 2010. For Australia, even though 2011 was the coolest year since 2001, the 2002–11 average temperature was the equal warmest 10-year period on record. But temperatures were not uniform across the country. While northern Australia was cooler than average, the South was actually warmer than average over the year. This was punctuated by three heatwaves: the January/February hot spell across the southern mainland, the early August heatwave across southeastern Australia and the period in late December which affected northwestern Australia.

During the January/February heatwave, Sydney had its longest hot spell in 152 years, with 7 consecutive days above 30˚C and 5 nights above 24˚C. This spell ended on the 6th of February 2011, when Sydney recorded its highest ever daily minimum temperature of 27.6˚C. Perth experienced some testing times in March with 22 consecutive days above 30˚C. The March daily average for 2011 in Perth was the highest on record at 31.9˚C. Despite these record-breaking occurrences, on average 2011 was generally a cold year Downunder, and for Australia that usually means more rain.

Mean rainfall for Australia in 2011 was 705 mm, and this makes 2011 the second wettest year since 1900. The combined rainfall from 2010 and 2011 was 1408 mm, which is the highest recorded two-year total, just one millimetre more than the next highest which was for 1973–74.

A number of records fell in this unusual year. March 2011 was the wettest March on record for Australia as a whole, and also for the Northern Territory and Queensland. January 2011 was the wettest January on record for Victoria, and February was the wettest February for South Australia. Even the West didn't miss out; overall, 2011 was also the wettest year on record for Western Australia.

And, of course, 2012 has started with more flooding in many parts of the country as the second La Niña showed its effects. But the situation seems to be stabilising, and a return to neutral conditions within the next few months is forecast.


Thank you for your comment. If it does not require moderation, it will appear shortly.
Facebook LinkedIn Twitter Add | Email Print

FlagPost

Flagpost is a blog on current issues of interest to members of the Australian Parliament


Parliamentary Library Logo showing Information Analysis & Advice

Archive

Syndication

Tagcloud

refugees asylum immigration Australian foreign policy Parliament climate change elections women social security Indigenous Australians Australian Bureau of Statistics Employment taxation Sport illicit drugs Medicare welfare reform Australian Defence Force welfare policy Asia income management Middle East criminal law disability Australian Sports Anti-Doping Agency World Anti-Doping Agency United States higher education people trafficking school education aid statistics Australian Electoral Commission WADA United Nations federal budget health financing emissions trading gambling Australia in the Asian Century steroids detention Private health insurance OECD ASADA labour force transport Law Enforcement Australian Federal Police Industrial Relations dental health National Disability Insurance Scheme forced labour Senate election results Papua New Guinea Australian Public Service International Women's Day corruption Fair Work Act child protection people smuggling debt federal election 2013 parliamentary procedure ALP New Zealand Australian Crime Commission Newstart Parenting Payment 43rd Parliament slavery by-election political parties Census constitution High Court skilled migration voting Federal Court terrorist groups Afghanistan Higher Education Loan Program HECS youth Aviation environment foreign debt gross debt net debt defence capability customs poker machines doping health crime health risks multiculturalism aged care Gonski Review of Funding for Schooling sex slavery sea farers leadership United Kingdom UK Parliament Electoral reform politics banking firearms public policy mental health China ADRV terrorism social media pensions welfare ASIO intelligence community Australian Security Intelligence Organisation governance public service reform Carbon Pricing Mechanism carbon tax mining military history employer employee fishing paid parental leave European Union same sex relationships international relations coal seam gas planning United Nations Security Council Australian economy food vocational education and training Drugs Indonesia children codes of conduct terrorist financing election timetable citizenship Productivity asylum seekers early childhood education Canada Population Financial sector national security fuel violence against women domestic violence disability employment Tasmania integrity science research and development Australian Secret Intelligence Service sexual abuse federal state relations World Trade Organization Australia accountability housing affordability bulk billing water renewable energy children's health health policy Governor-General US economy export liquefied natural gas foreign bribery question time speaker superannuation family assistance expertise Senators and Members climate Intergovernmental Panel on Climate Change Department of Agriculture Fisheries and Forestry food labelling Pacific Islands reserved seats new psychoactive substances synthetic drugs UNODC carbon markets health reform Indigenous constitutional recognition of local government local government consumer laws PISA royal commission US politics language education Leaders of the Opposition Parliamentary remuneration health system Australia Greens money laundering servitude Special Rapporteur Trafficking Protocol energy forced marriage rural and regional Northern Territory Emergency Response ministries social citizenship China; Economic policy; Southeast Asia; Africa housing Speaker; House of Representatives; Parliament Defence High Court; Indigenous; Indigenous Australians; Native Title ACT Indigenous education Norfolk Island External Territories emissions reduction fund; climate change child care funding refugees immigration asylum procurement Indigenous health e-voting internet voting nsw state elections 44th Parliament 2015 ABS Age Pension Death penalty capital punishment execution Bali nine Bali bombings Trade EU China soft power education Fiji India Disability Support Pension Antarctica Diplomacy by-elections state and territories workers Bills anti-corruption fraud bribery transparency corporate ownership whistleblower G20 economic reform innovation standards NATO Members of Parliament Scottish referendum Middle East; national security; terrorism social services Criminal Code Amendment (Misrepresentation of Age to a Minor) Bill 2013 online grooming sexual assault of minors ACT Assembly public health smoking plain packaging tobacco cigarettes Asia; Japan; international relations Work Health and Safety Migration; asylum seekers; regional processing China; United States; international relations fiscal policy Racial Discrimination Act; social policy; human rights; indigenous Australians Foreign policy Southeast Asia Israel Palestine regional unemployment asylum refugees immigration political finance donations foreign aid Economics efficiency human rights; Racial Discrimination Act employment law bullying Animal law; food copyright Australian Law Reform Commission industry peace keeping contracts workplace policies trade unions same-sex marriage disorderly conduct retirement Parliament House standing orders public housing prime ministers sitting days First speech defence budget submarines Somalia GDP forestry world heritage political engagement leave loading Trade; tariffs; safeguards; Anti-dumping public interest disclosure whistleblowing Productivity Commission regulation limitation period universities Ireland cancer gene patents genetic testing suspension of standing and sessional orders animal health live exports welfare systems infant mortality middle class welfare honorary citizen railways disciplinary tribunals standard of proof World Health Organisation arts international students skilled graduate visas temporary employment visas apologies roads Italy national heritage NHMRC nutrition anti-dumping Constitutional reform referendum Rent Assistance competition policy pharmaceutical benefits scheme obesity evidence law sacrament of confession US presidential election international days baby bonus DFAT UN General Assembly deregulation Regulation Impact Statements administrative law small business Breaker Morant homelessness regional engagement social determinants of health abortion Youth Allowance Members suspension citizen engagement policymaking federal election 2010 workplace health and safety Trafficking in Persons Report marine reserves hearing TAFE Victoria astronomy resources sector YMCA youth parliament alcohol Korea rebate Australian Greens presidential nomination Racial Discrimination Act entitlements political parties preselection solar hot water Financial Action Taskforce Horn of Africa peacekeeping piracy Great Barrier Reef Stronger futures political financing Hung Parliament political education social inclusion Social Inclusion Board maritime early childhood National Quality Framework for Early Childhood Education and Care Murray-Darling Basin Iran sanctions

Show all
Show less
Back to top