Annual Australian Climate Statement 2012

The first half of 2012 was cooler and wetter than average, and the second half was warmer and drier than average. The change from wet to dry conditions was consistent with changing sea surface temperatures in the tropical Pacific and Indian Oceans, which are a primary driver of rainfall variability across much of Australia.

The Australian mean rainfall total for 2012 was 476 mm (11 mm above the long-term average of 465 mm); with the year ranked near the median of historical observations. This contrasts with 2011's high annual total of 699 mm.

The Australian area-averaged mean temperature for 2012 was 0.11 °C above the 1961–1990 average of 21.81 °C. Australia has experienced just one below-average year in the last decade (2011). Cooler-than-average conditions were recorded in northern Australia and parts of the east while Tasmania, the mainland's southern coast, and the southwestern half of Western Australia experienced above-average temperatures.

In 2012, maximum temperatures were 0.51 °C above average, and minimum temperatures 0.28 °C below average. While both 2011 and 2012 were cooler than recent years, the last decade (2003–2012) has been one of Australia's warmest on record; with an anomaly of +0.44 °C, the fifth-warmest 10-year period on record.

Conditions at the start of 2012 were consistent with the presence of a moderately strong La Niña event in the tropical Pacific, which typically brings wetter and cooler conditions to eastern Australia. The tropical Pacific returned to neutral conditions by mid-autumn 2012, followed by the emergence of El Niño-like conditions during winter and spring. El Niño events are typically associated with drier-than-average conditions across the mainland.

Australian monthly rainfall totals (blue bars), compared to the historical average (black line).

The first three months of the year saw above-average rainfall for most of the country, especially across the eastern mainland. March was the third-wettest on record for Australia, a result dominated by rainfall in the eastern States. New South Wales recorded its second-highest March total (the highest occurred in 1956), Victoria the third-highest (highest since 1950), and Queensland the fifth-highest.

From April onwards rainfall was generally below average for most of the southern mainland while parts of the north continued to record above-average rainfall.

El Niño and La Niña events are determined by, amongst other indicators, the strength of sea surface temperature anomalies in the tropical Pacific Ocean; with La Niña associated with cooler-than-average temperatures and El Niño warmer-than-average temperatures. The transition from cool, La Niña conditions to warmer ocean temperatures occurred during winter and persisted until September of 2012. Although Pacific climate indicators remained near, or just in excess of, the values generally associated with an El Niño event, these values were not maintained for a sufficiently long period for 2012 to be considered an El Niño year. The Pacific returned to neutral (neither El Niño nor La Niña) by mid-spring, and remained so to year's end.

Australian rainfall is also strongly influenced by sea surface temperatures in the Indian Ocean. A positive Indian Ocean Dipole event, associated with cooler waters off the northwest coast of Australia and typically drier conditions across parts of the continent, emerged in early August and continued into October. This likely contributed to drier-than-average conditions across the southern mainland.

The year also saw unusually persistent high atmospheric pressure near southern Australia. This was associated with greatly suppressed westerly frontal and storm activity in southwest Australia, and indeed southern Australia as a whole, and was reflected in very poor winter–spring rainfall in many southern areas.

Australia's rainfall for 2012 ranks near the middle of historical observations with an annual total 11 mm above average, making 2012 the fortieth-wettest year in 113 years of record. All States and Territories, except South Australia, recorded near-average annual rainfall within 10 per cent of the long-term average; South Australia recorded the largest departure at 23 per cent below average. This follows on from exceptional rainfall in 2010 and very-much-above-average rainfall across most of Australia in 2011. The two calendar years 2010 and 2011 were the wettest two-year period on record for Australia, while the 24 months from April 2010 to March 2012 were the wettest 24-month period on record.

The La Niña at the start of the year continued to bring very heavy rainfall over much of mainland Australia. January–March rainfall was well above average in most regions, with only the eastern Top End and some seasonally dry parts of the far south of Western Australia recording significantly below-average falls. Nationally it was the seventh-wettest January–March quarter on record (32 per cent above average).

From April onwards, rainfall was generally below to very much below average across the southern half of the mainland. Nationally, totals were below average in eight of the nine months (June being the only exception). The April–December total nationally was 25 per cent below average, the twentieth-lowest on record.

Western Australia (which had its third-driest April to October growing season on record) and northern South Australia were especially dry, with rainfall mostly in the lowest 10 per cent of historical records, and record-low totals over wide (although mostly sparsely populated) areas for April–October. Oodnadatta, in northern South Australia, recorded only 8.8 mm of rainfall for the 9 months April–December. No rain fell at Alice Springs Airport in the 157 days from 25 April to 28 September, the longest rainless period in the site's 71-year history. The only substantial area where rainfall was significantly above average was northern inland Queensland.

For southwest Western Australia July rainfall was the lowest on record. Other notable monthly rainfall totals include lowest-on-record October rainfall for southern Australia (the region south of 26°S) and the eleventh-wettest November, and eighth-wettest December, on record for southwest Western Australia (the region southwest of a line from Jurien Bay to Bremer Bay). The year reinforced the recent pattern of below-average cool season (April to October) rainfall across much of southern Australia.

The annual mean temperature for 2012 returned to above average values, after being cooler than average for 2011. Mean temperatures were 0.11 °C above average for the year as a whole. Cooler-than-average conditions predominated in northern and eastern Australia while Tasmania, the mainland's southern coast, and the southwestern half of Western Australia experienced above-average temperatures.

For the year as a whole, maximum temperatures were 0.51 °C above average. All States and Territories recorded a positive anomaly for their area-averaged value. Some areas of coastal Western Australia observed highest-on-record annual maxima. Below-average maxima were recorded in Queensland between the Gulf coast and Rockhampton and a pocket of inland Western Australia and the Northern Territory.

Widespread cloud cover and rainfall typically brought by a La Niña is associated with cooler daytime temperatures for Australia, and this was observed with a cool start to 2012. Maximum temperatures were below average in the north and east of the country between January and March, and over northern Australia until July. However, even during these months, maxima along the western coast of Western Australia were significantly above average; an effect associated with the unusual warmth of the ocean waters surrounding this region (see Sea surface temperatures in the Australian region below).

Daytime maximum temperatures became warmer from August onwards. In the August–December period they were 1.58 °C above average nationally (the second-highest on record), whilst for Western Australia they were 1.62 °C above average, just 0.16 °C below the record high set in 2006. Individual months saw record-high maxima recorded in the Kimberley and Pilbara for August, in northeastern South Australia for November, and parts of the far northern coast for December.

For the year as a whole, minimum temperatures were 0.28 °C below average. Minima were below average across much of northern and central Australia as well as New South Wales west of the Great Divide. A large part of this area recorded minima in the lowest decile. Minimum temperatures were the eleventh-coolest on record for the Northern Territory (0.80 °C below average). A combination of abnormal southerly flow across eastern Australia, surface soil moisture from the very heavy rainfall between 2010 and summer 2011–12, and below-average cloudiness during winter and spring contributed to the cooler-than-average minimum temperatures. In contrast, Tasmania's minimum temperatures (0.43 °C above average) were the tenth-warmest on record. Above-average minimum temperatures were restricted to the coastal fringes of western and southern Western Australia, Victoria and southeastern South Australia, the tip of the Cape York Peninsula, and Tasmania.

The dry season in northern Australia was notably cooler than average, with minimum temperatures in the Northern Territory 2.03 °C below average for the May–August period, ranking second behind 1976. This was mostly the result of persistently cool nights rather than individual extreme events. One significant record occurred at Darwin, which had its coldest August night with 13.1 °C on 13 August. Winter ranked as the third-coolest on record nationally for minimum temperatures (0.91 °C below average), and coolest for the Northern Territory, while autumn (0.93 °C below average) was the fourth-coolest nationally. Western Australia generally experienced above- to very-much-above average minima from August onwards, while November and December minima were particularly warm for nearly all of Australia.

The large contrast between warm maxima and cool minima resulted in the mean diurnal temperature range being the third-highest on record. The more extreme years of 1994 and 2002 also saw severe drought over most of Australia.

Flooding affected many parts of eastern Australia as the 2011–12 La Niña continued into early 2012. Persistent heavy rain in late January across the north coast of New South Wales and southeast Queensland was followed in early February by rain in inland northern New South Wales and southern inland Queensland. Locations in the Condamine–Balonne system reached record flood peaks, while at Moree the Mehi River reached its highest level since 1976, and at Charleville the Warrego River reached its highest level since 1990, although major urban inundation was averted in both centres. Flooding continued on the Darling River system over several months as floodwaters travelled downstream.

One of the most extreme multi-day rainfall events in southeast Australia's history occurred between 27 February and 4 March, as widespread unstable conditions brought daily rainfall totals between 50 and 100 mm over a broad area of northern Victoria, southern New South Wales, and eastern South Australia. For the Murray–Darling basin as a whole, this event was the wettest 7-day period on record for any month since at least 1900, with catchment averages for the Upper Murray (294.4 mm), Murrumbidgee (202.6 mm) and Lachlan (180.1 mm) all nearly double their previous record-high for any 7-day period. There were extensive evacuations in towns including Wagga Wagga, Hay, and Forbes and extensive overland flooding in the Riverina and central and northern Victoria. Flooding also affected rivers in central and south coast New South Wales, the Australian Capital Territory, northeast Victoria, and central Australia while flash flooding affected far western New South Wales and eastern South Australia.

In the second half of March a tropical low struck Darwin, the eastern Top End, and western Kimberley before bringing heavy rain to northern Queensland and flooding on the central and north Queensland coast. Another low brought heavy rain and flash flooding to southeast Queensland on 23 March.

An East Coast Low caused major flooding in eastern Victoria from 3–5 June. The Yallourn open-cut coal mine at Morwell was flooded, and many roads were closed. Flooding also affected the Otway Ranges west of Geelong, where many locations received more than twice their average monthly rainfall in a day, while high winds were felt across southern Victoria and on the New South Wales coast. Less severe floods also affected eastern Victoria in late May and late June.

A deep low pressure system crossed southwest Western Australia during 7–13 June bringing heavy rain and significant storm and tornado damage to the region. Damage to the electricity network over the week was the worst in Western Australia's history, with power lost to more than 170 000 homes. Significant storm surges were recorded during the event, with the largest on the 10th, reaching approximately 0.8 m around Perth and 1.0 m in Fremantle setting a new record for high sea level.

There were eight tropical cyclones in the Australian region during the 2011–12 season, below the long-term average of eleven. Five occurred between January and March. The strongest, Lua, reached category 4 intensity and made landfall at that intensity on 17 March near Pardoo, east of Port Hedland. Lua produced heavy rain across the Kimberley and Pilbara, penetrating far inland across the interior of Western Australia as it decayed. Lua was the only cyclone to reach this intensity over the Australian region, although Jasmine, in early February, reached category 4 and brought flooding to a number of Pacific islands after moving eastwards out of the Australian region. The other significant landfall of the season was Heidi, a category 2 system which made landfall near Port Hedland on 12 January, causing relatively minor damage and power outages.

Numerous winter and spring heat records were set in various parts of Australia as maximum temperatures tracked well above average from August onwards. Alice Springs equalled its record high temperatures for both September (38.8 °C, 22 September) and October (41.7 °C, 24 October). September records were also set at Woomera (38.6 °C, 27 September) and Mount Isa (39.8 °C, 23 September), while Evans Head reached 41.6 °C on 20 October, the highest October temperature on record for any coastal New South Wales site. Birdsville had its earliest spring 40-degree day when it reached 40.6 °C on 20 September, while other notable early-season records included Perth (34.3 °C, 1 October) and Ceduna (44.0 °C, 4 November).

One of the most significant spring heatwaves on record affected much of eastern Australia at the end of November. A large, hot air mass in central Australia was drawn southeastwards bringing widespread maxima in the low to mid-40s throughout northern and eastern South Australia, adjacent parts of Queensland, inland New South Wales, and northern Victoria. Temperatures peaked on 29 November, with Ouyen in Victoria's Mallee reaching 45.8 °C, a new Victorian record high for spring. The old record of 44.5 °C, set 17 November 1980 at Mildura, was also broken by Mildura (45.5 °C), Hopetoun (45.0 °C), Swan Hill (44.8 °C), and Walpeup (44.7 °C). In New South Wales the highest temperature was 46.2 °C at Pooncarie (that State's fourth-highest November maxima, and highest November temperature outside of November 2009), while in South Australia Oodnadatta broke that State's record for warmest overnight November temperature with a minimum of 32.3 °C (the previous record was 32.2 °C, also at Oodnadatta, on 30 November 2006).

Sea surface temperatures (SSTs) in the Australian region were not as high as those seen in the record breaking year of 2010, and slightly cooler than 2011, but continued the long run of above-average temperatures. No year since 1995 has recorded below-average SSTs. Based on preliminary data to November, 2012 ranked as the equal-sixth-warmest year since 1910, at 0.36 °C above average. SSTs in the Australian region were in the top 12 observations for 10 out of 11 months. The most recent ten years (2003–2012) had a 10-year anomaly of +0.33 °C, which was tied with 2002–2011 and 1997–2006 as the equal-fourth-warmest 10-year period since 1910 for SSTs in the Australian region, 0.01 °C below the record 10-year value held jointly by 2001–2010, 1998–2007, and 1996–2005.

SSTs were consistently above average in the southern Indian Ocean off the coast of Western Australia throughout the year, a pattern which has persisted for the past three years. For the southwest region (the area of ocean west of the coast between Learmonth and Cape Leeuwin in Western Australia) winter seasonal SST anomalies were the highest on record, while summer (2011–12), autumn, and spring were the second highest.

Preliminary data released by the World Meteorological Organization (WMO) on 28 November estimated the global mean temperature for 2012 (January–September) to be 0.43 ±0.11 °C above the 1961–1990 annual average of 14.0 °C. Based on these preliminary figures, 2012 ranks as the ninth-highest on record. No year since 1985 has recorded a below-average global mean temperature, and the years between 1997 and the present have been the 14 warmest on record. The 10-year global average for 2003–2012 was 0.45 °C above average, making it the third-warmest 10-year period since 1880.

The Bureau of Meteorology is responsible for collecting, managing and safeguarding Australia's climate archive. Several homogenised datasets have been developed from this archive to identify, monitor and attribute changes in the Australian climate. Extensive analyses have been undertaken on these data to ensure they have not been unduly affected by changes in site location, urbanisation, exposure or instrumentation over time.

This year's statement has been prepared using the updated homogenised Australian temperature dataset, ACORN-SAT. ACORN-SAT data can be accessed at: http://www.bom.gov.au/climate/change/acorn-sat/. High-quality rainfall data (from the same dataset as previous years) can be accessed at: http://www.bom.gov.au/climate/change/datasets/datasets.shtml.