Annual Australian Climate Statement 2011

Issued 4 January 2012

Note that all values in this statement are as compiled on January 3. Subsequent quality control and new data availability may see minor changes to final values.

Consecutive La Niña events bring Australia's third-wettest year on record and second-highest two year total.

  • La Niña brings heavy rain, eases drought and causes widespread flooding.
  • Second-highest two-year (2010-2011) rainfall on record.
  • Australia's first cooler than average year since 2001.
  • Australia's coldest autumn since at least 1950.
  • The 10 years from 2002 to 2011 Australia's equal-warmest 10-year period on record.

Overview

2011 was another wet year for Australia, with data collected by the Bureau of Meteorology showing that the Australian mean rainfall total for 2011 was 699 mm (234 mm above the long-term average of 465 mm), placing the year at the third-wettest since comparable records began in 1900. Back-to-back La Niña events led to a two-year rainfall total of 1402 mm which is the second-highest total on record behind 1407 mm in 1973-74.

The 2010-11 La Niña, one of the strongest on record, continued to dominate climate patterns during the first part of 2011 before decaying in autumn. A second La Niña developed in spring 2011 and, although weaker than the first event, was associated with rainfall significantly above average across much of the country. It is likely that a record warm eastern Indian Ocean also contributed to above average rainfall in 2011.

From January to March, rainfall was generally very much above average in most areas, and April was rather wet over the north of Western Australia and the Northern Territory. Falls greater than 300 mm across much of the tropical north led to the wettest March on record for Australia as a whole, with average rainfall of 149 mm topping the previous 1989 record by 23 mm. The period from May to September (when La Niña had receded) saw rainfall below average for most of the country. October was very wet in the western half of the country, with Western Australia experiencing its third-wettest October on record. November rainfall was above average for most of the country, while December was wet for the southwest and parts of Queensland. For the year as a whole, the majority of Australia received above average rainfall; the only regions with below-average rain were patches of southwest Western Australia, western Tasmania and pockets of New South Wales and southeast Queensland.

2011 Australian rainfall deciles map

2011 annual rainfall compared against historical rainfall records.

The Australian area-averaged mean temperature in 2011 was 0.14 °C below the 1961 to 1990 average of 21.81 °C. This was the first time since 2001 (also a wet, La Niña year) that Australia's mean annual temperature was below the 1961-90 average. Even though, when taken over the whole country, the mean temperature was below average, the southern half of Australia was warmer than usual.

In 2011, maximum temperatures averaged 0.25 °C below normal across the country, while minima averaged 0.03 °C below normal. Contrasting this, the global mean temperature in 2011 was the highest for any year which began with a La Niña. Australia was one of the few places on the globe to experience cooler than average temperatures in 2011.

Despite the slightly cooler conditions in Australia in 2011, the country's 10-year average continues to demonstrate the rising trend in temperatures, with 2002-2011 likely to rank in the top two warmest 10-year periods on record for Australia, at 0.52 °C above the long-term average.

A tale of two La Niñas - Australia's second-wettest two-year period on record

Rainfall during 2011 was very much above average across most of Australia, with record high falls over the Kimberley, south-eastern and central Western Australia, and across parts of the north of the Northern Territory. Based on preliminary numbers, 2011 was the third-wettest year on record for Australia as a whole and the Northern Territory, second-wettest for Western Australia, and fourth-wettest for northern Australia (north of 26°S).

A very heavy tropical monsoon season was associated with exceptional summer rainfall over most of Australia. Victoria recorded its wettest January in 112 years of records and its third-wettest February (highest statewide total since 1973). February was also the second wettest on record for Australia and Western Australia, and the wettest on record for South Australia. March was the wettest on record for Australia as a whole, as well as for the Northern Territory and Queensland, and the third-wettest for South Australia.

Even as the La Niña decayed from late April, the Kimberley and the north of the Northern Territory continued to see very much above average rainfall. All states recorded below average May rainfall. June was notable for the lack of rainfall in the southeast - the main rainfall deficiencies observed in 2011 occurred during winter and early spring in the southeast of Australia.

As has occurred several times in the historical record, La Niña conditions redeveloped during spring and continued beyond the end of 2011. Although it was significantly weaker than the 2010-2011 event, it has occurred in conjunction with record warm conditions across the eastern Indian Ocean. October was very wet in the western half of the country, while November rainfall was generally above to very much average in most regions except for coastal Queensland. December rainfall was very much above average for much of southwest Western Australia, with some inland parts recording highest falls on record. Above average December rainfall was also recorded over much of Queensland and adjacent areas of the Northern Territory, South Australia and New South Wales.

2011 Australian total rainfall timeseries

2011 Annual and decadal mean rainfall (mm) for Australia since 1900. The average for the past 10 years is shown in darker grey.

First cooler than average year since 2001, courtesy of persistent wet weather. However, equal-warmest 10-year period on record.

For the first time in a decade, Australia's annual mean temperature was below the 1961-1990 average. Daytime maximum temperatures were suppressed over much of the mainland as a result of the heavy rainfall at both the start and end of 2011, and relatively frequent southerly airstreams in the first half of the year.

For the year as a whole, both minimum and maximum temperatures were below to very much below average in the tropics and subtropics. In contrast, mean temperatures were above average for most of southern Australia.

Widespread below average daytime temperatures were notable between February and May, while August maxima were very much above average for most of Australia, excluding the tropics. In November, maximum temperatures were once again well below normal in the northwest of the country. Unusually warm overnight temperatures were a feature in southern Australia in a number of months, including January, July, August, and October. Meanwhile, May and June produced exceptionally low overnight temperatures across northern Australia: in a large area of the Kimberley and the north of the Northern Territory minima were the lowest on record.

2011 was clearly the warmest year on record for southwest Western Australia including Perth, with mean temperatures for the region 1.16 °C above the 1961 to 1990 average, and 0.41 °C above the previous record, set in 1999.

Annual Australian mean temperature timeseries

Annual and decadal mean temperature anomalies for Australia (compared with 1961 to 1990 average). The average for the past 10 years is shown in darker grey.

Averaged over Australia, autumn mean temperatures were 1.15 °C below the historical average, the coolest since comparable records began in 1950. Maximum temperatures were the second-coolest on record and minima the fifth-coolest. These months were particularly cool across the tropics. Parts of the eastern Kimberley and the Northern Territory (equating to 8.4% of Australia's total area) experienced their lowest autumn maximum temperatures on record, while the Northern Territory as a whole experienced its coldest autumn on record.

The start to the dry season was the coldest on record over the Northern Territory as a result of persistent low temperatures in the northern tropics from late May to mid-June. The Northern Territory was particularly cool in May, including a Territory record for May of −4.2 °C at Arltunga on the 31st, and a May record of five consecutive nights below 0 °C at Alice Springs, between 27 and 31 May. In June, the Northern Territory saw six consecutive days in which the temperature remained below 15 °C in at least one location over the region, the longest such streak for any month since 1998. In addition, for the first time ever Darwin's minimum temperature dropped below 20 °C every night during June. This was the fourth-longest run of cool nights in the Northern Territory capital since records began at the airport in 1941.

2011 Australian mean temperature deciles map

2011 annual mean temperatures compared against historical temperature records.

Southern Australia experienced two notable heat events during 2011. The first was a heatwave lasting from late January to early February across the southern mainland. Maximum temperature records were set in southeast Western Australia and central South Australia, including an all-time record of 48.1 °C at Woomera on 25 January. Sydney experienced its longest hot spell in 152 years of record with seven consecutive days above 30 °C and 5 nights above 24 °C.

The second heat event occurred during early August when a high pressure system brought unseasonable early season warmth to south-eastern Australia. Melbourne set an early-season record high overnight temperature of 17.3 °C on 4 August and averaged over the month, it was the warmest August on record for Tasmania.

The highest temperatures for the year occurred in December 2011 affecting the Pilbara region. Multiple sites broke the previous Western Australia December record (48.8 °C at Mardie on 26 December 1986) over three consecutive days. Roebourne recorded 49.4 °C on 21 December, while Onslow Airport recorded 49.2 °C on the 22nd and Learmonth 48.9 °C on the 23rd. Roebourne's 49.4 °C was the highest temperature recorded in Australia since 1998.

The influence of La Niña on Australian temperatures

In general, widespread cloud cover and rainfall are associated with cooler daytime temperatures for Australia. For this reason, Australian average temperatures are generally cooler during La Niña years. This is particularly true for years with strong and sustained La Niña conditions, accompanied by high rainfall across large parts of the continent. Eight of the last nine years with sustained La Niña conditions recorded a cooler than normal Australian average temperature, with four of those years experiencing very cool conditions.

Annual Australian mean temperature anomalies for strong La Niña years since 1950

Annual mean temperature anomalies for Australia (compared with 1961 to 1990 average), with La Niña years marked in teal (nine La Niña years in total, including 1989). La Niña years are defined as those where central Pacific sea surface temperature anomalies exceeded −1 °C for a sustained period leading into the start of the year.

Flooding, storms, and fires

The 2010-11 La Niña event directly contributed to numerous and significant floods that continued throughout the summer and into autumn 2011. The period from late November 2010 to mid-January 2011 was extremely wet through much of eastern Australia, with cumulative rainfall resulting in flooding which was amongst the most significant in Australia's recorded history.

The most notable flood events for the year occurred in southeast Queensland and nearby areas of northern New South Wales, where many catchments were already subject to, or recovering from, flooding. Around Rockhampton, in the Fitzroy basin, flooding continued into early January. During the second week of January severe river and flash flooding affected the Brisbane catchments. This also affected nearby towns including Toowoomba and Grantham, resulting in loss of life and extensive property damage. On 13 January Brisbane recorded its second-highest flood level in the last 100 years, after January 1974.

Northern Victoria also experienced notable and damaging flooding following exceptional summer rainfall; initially from mid-January with flash flooding in the Grampians and surrounding areas and riverine flooding downstream in the Wimmera and Loddon catchments. February brought renewed flooding to these regions and additional flash floods in central Victoria. Some of the riverine flooding in northern and western Victoria was long-lived, with flatter parts of the lower catchments inundated for many weeks. There was also significant flooding in northern Tasmania and southern inland New South Wales at this time.

Many other floods occurred during the year. A monsoonal burst in mid-March resulted in extensive flooding isolating communities across the Fitzroy, Ord and Pentecost River catchments in the eastern Kimberley, as well as causing prolonged flooding in many catchments through western Queensland and along the tropical coasts. Other notable floods occurred in central Victoria, the south coast of NSW and eastern Tasmania in late March; southeast Victoria, together with northern and eastern Tasmania in mid-April; and the NSW coast in mid-June. Major floods also occurred in northern inland New South Wales west of the Great Dividing Range, as well as in inland Queensland, in the latter part of November and early December.

A number of significant tropical cyclones affected northern Australia in 2011. Tropical cyclone Anthony crossed the central Queensland coast near Bowen on 30 January as a marginal Category 2 storm, while tropical cyclone Bianca brought rain and strong winds to the Kimberley and Pilbara coast in late January. Tropical cyclone Yasi, the strongest cyclone to make landfall in Queensland since at least 1918 (another La Niña year), crossed the coast near Mission Beach, between Cairns and Townsville, on 3 February causing extensive damage. The slow-moving tropical cyclone Carlos brought very heavy rainfall to the Top End between 15 and 17 February, breaking numerous records, including the highest daily rainfall at Darwin Airport with 367.6 mm on the 16th and highest 3-day total at Darwin Airport with 684.8 mm.

Damaging storms were also a feature of the year, with numerous thunderstorms when La Niña conditions were dominant in summer and spring. In addition to the previously mentioned events, severe thunderstorms brought extreme rainfall to parts of Victoria, causing flash flooding around Mildura, the Melbourne metropolitan region and eastern Victoria during 4 February. Daily rainfall totals of 100-200 mm were widespread during the event. Further severe storms with large hail and a tornado affected areas near Melbourne on 25 December with widespread damage to cars and houses.

The very high rainfall during 2010 and 2011 was accompanied by strong vegetation growth across the usually arid inland. This provided ample fuel for grassfires in central Australia in the dry season (winter and spring), with widespread fires in more remote regions in the south of the Northern Territory and central and western Queensland. Significant fires also occurred in the south-west of Western Australia. In early February fires burnt out of control near Red Hill, in the Swan Valley, and in the Roleystone and Kelmscott areas over 100 homes were destroyed or partially damaged. Late in the year a number of houses were destroyed by fires near Margaret River in Western Australia.

Sea Surface Temperatures in the Australian Region

Sea-surface temperatures (SSTs) in the Australian region were slightly cooler than 2010, but were still 0.39 °C above average. The most notable monthly average anomalies were January, ranking second (+0.39 °C), and November, third (+0.43 °C), warmest on record. Furthermore, during 2011, 9 out of 11 months ranked in the top 10 warmest observations on record for their respective months. Conditions were particularly warm in the eastern and southern Indian Ocean with record warm conditions occurring in autumn, winter, and spring to the west of Perth.

SSTs in the tropical Pacific Ocean show the clear pattern of a La Niña event; below average SSTs in the central to eastern Pacific and above average SSTs in the western Pacific region. The La Niña pattern was also apparent below the surface across the tropical Pacific. Sub-surface temperature anomalies in the western Pacific reached a peak of 4 °C above the long-term average during February 2011, before later weakening. Temperatures below the surface of the eastern Pacific approached 4 °C below normal through spring 2011.

The past ten years (2002-2011) has seen the warmest 10-year averaged SSTs in the Australian region since 1910.

Annual Australian sea surface temperature timeseries

Annual and decadal mean sea surface temperature anomalies in the Australian region (compared with 1961 to 1990 average). The average for the past 10 years is shown in darker grey.

Globally, 2011 the warmest La Niña year on record

Preliminary data released by the World Meteorological Organization (WMO) on 29 November estimated the global mean temperature for 2011 (January-October) at 0.41 °C ±0.11 °C above the 1961 to 1990 annual average of 14.0 °C. At present, 2011's nominal value ranks as the equal tenth-highest on record, with the 13 warmest years having all occurred in the 15 years since 1997. The 10-year global average from 2002-2011 was 0.46 °C above normal, making it the equal-hottest 10-year period on record.

Of the 23 climate regions monitored by the WMO globally, northern Australia was the only region to record cooler than normal temperatures during 2011, in association with very heavy rainfall.

Years commencing with a strong La Niña are typically 0.10 to 0.15 °C cooler than the years preceding and following them. Although global temperatures have not been as warm as the record-breaking values seen in 2010, 2011 was the warmest La Niña year on record.

Accessing Australia's climate change datasets

The Bureau of Meteorology is responsible for collecting, managing and safeguarding Australia's climate archive. Several high-quality datasets have been developed from this archive to identify, monitor and attribute changes in the Australian climate. Extensive rehabilitation work has been undertaken on these data to ensure they have not been compromised by changes in site location, urbanisation, exposure or instrumentation over time.
The high-quality data can be accessed at: http://www.bom.gov.au/climate/change/hqsites/

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