February 2009

Southeast Australian heatwave: the hottest in 100 years

Introduction

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An exceptional heatwave affected south-eastern Australia during late January and early February 2009. The most extreme conditions occurred in northern and eastern Tasmania, most of Victoria and adjacent border areas of New South Wales and southern South Australia, with many records set both for high day- and night-time temperatures as well as for the duration of extreme heat.

There were two major episodes of exceptional high temperatures, from 28-31 January and 6-8 February, with slightly lower but still very high temperatures persisting in many inland areas through the period in between. 

Widespread very hot conditions began to develop in the southeast from 27 January onwards. The presence of a slow-moving high pressure system in the Tasman Sea, combined with an intense tropical low off the north-west coast of Western Australia and an active monsoon trough, provided the ideal conditions for hot air of tropical origin to be directed over the southern parts of the continent.   The initial acute phase of the heatwave extended from 28 to 30 January, with many individual-day records set on those days. A weak change brought some relief to southern coastal areas from 31 January onwards, but inland areas, as well as much of South Australia, remained very hot until 5 February. Extreme heat then returned throughout most of the region (except Tasmania), peaking on 7 February when record high temperatures were set across most of Victoria, before the Tasman Sea high finally moved away on 8 February.

The first stage of the heatwave:  27-31 January

In the first stage of the heatwave, the most exceptional heat, compared with historic experience, occurred in northern and eastern Tasmania. The previous state record of 40.8°C, set at Hobart on 4 January 1976, was broken on 29 January when it reached 41.5°C at Flinders Island Airport. This record only lasted one day, as Scamander, on the east coast, reached 42.2°C on 30 January. Four other sites broke the previous Tasmanian record that day, St Helens (41.8°C), Ross (41.6), Cressy (41.4°C) and Fingal (41.3°C). Fingal also reached 40.6°C on 29 January, only the second time that a Tasmanian site has reached 40°C on two successive days.

Nearly half of Tasmania had its hottest day on record on 30 January with many records broken by large margins, particularly in the north. Launceston Airport (39.9°C) broke its previous record (37.3°C) by 2.6 °C. This is the second-largest margin by which a record high maximum has been broken at any of the 103 locations in the long-term high-quality Australian temperature dataset. Launceston Airport also reached 37.2°C and 37.5°C on 29 and 31 January, respectively, meaning that three of the four warmest days on record at the site now come from the 2009 heatwave. (Whilst the Launceston Airport site was not open in January 1939, data from Launceston city indicate the temperatures in that year were well below 2009 levels).

railway  

 

The extreme heat buckled railway lines.

The January-February 2009 event was responsible for seven of the eight highest temperatures on record in Tasmania; a total of eight sites reached 40°C, a mark which had only been reached on 16 previous occasions in the state’s recorded history. Another unusual feature of the event was that the highest temperatures occurred in the state’s northern half, whereas most extreme high temperatures in Tasmania (including all 16 previous observations of 40°C or above) had been in the south-east around Hobart, or on the east coast from Swansea southwards. 

In southern South Australia, and much of central, southern and western Victoria, maximum temperatures widely reached their highest levels since at least 1939. Melbourne and Adelaide both narrowly missed all-time records during this initial heatwave period. Melbourne’s 45.1°C on 30 January was the second-highest on record behind 45.6°C on 13 January 1939, while Adelaide’s 45.7°C on 28 January ranks third behind two 1939 readings of 46.1°C and 45.9°C. At a few mainland locations, including Geelong (45.3°C on 29 January) and Wilsons Promontory (41.4°C on 30 January), even the 1939 marks were surpassed, while post-1939 stations where all-time records were set or equalled included Nuriootpa, Mount Barker, Cape Borda, Keith and Mount Gambier (SA), Omeo and Mangalore (Victoria), and Tumbarumba (NSW). 

South Australia’s highest temperature during this part of the event was 48.2°C at Kyancutta on 28 January, while Victoria’s peak was 45.8°C at Avalon Airport on 29 January and Charlton on 31 January. Another notable reading was 48.0°C at Pallamana, near Murray Bridge, on the 28th. These values fell short of state records (which are 50.7°C and 47.2°C for SA and Victoria, respectively). 

Overnight minimum temperatures were also very high in many places during this part of the event. Adelaide experienced its warmest night on record when the temperature only fell to 33.9°C in the early hours of 29 January, and other site records included those at Ceduna and Murray Bridge. In Victoria, Melbourne Airport’s minimum of 30.5°C on 29 January was only 0.4°C short of the Victorian record, set at Mildura in 1999 and Kerang in 2001, while Melton Mowbray’s 24.0°C on 30 January was the fourth-highest January minimum on record for Tasmania. The extremely high day and night temperatures combined for a record high daily mean temperature at Melbourne (35.4°C on 30 January), which, along with the previous day (35.0), were the first time Melbourne’s daily mean temperature has exceeded 35°C. 

On the morning of 29 January, an exceptional event also occurred in the northern suburbs of Adelaide around 3 a.m. when strong north-westerly winds mixed hot air aloft to the surface. At RAAF Edinburgh, the temperature rose to 41.7°C at 3.04 a.m. Such an event appears to be without known precedent in southern Australia. 

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The second acute stage of the heatwave – 6-8 February

 After a slight drop in temperatures during the first few days of February, extreme heat returned to the south-east on 6 February. Temperatures rose sharply in South Australia and western Victoria on 6 February, but it was 7 February which saw the most exceptional heat of the whole event.

Alex Koppel/Associated Press/News Ltd   fire

On 7 February, the focus of the most extreme heat, which was accompanied by high winds and very low humidity, was in Victoria. An all-time state record was set at Hopetoun, in the state’s north-west, when the temperature reached 48.8°C, exceeding the old record of 47.2°C, set at Mildura in January 19395 by a considerable margin. Seven other sites, in the Wimmera and in the area immediately west of Melbourne, also exceeded the old record, including Avalon Airport (47.9°C), Horsham (47.6°C), Longerenong (47.6°C) and Laverton (47.5°C). The Hopetoun  temperature is also believed to be the highest ever recorded in the world so far south. A total of 14 sites exceeded the previous Victorian February record of 46.7°C.6

Many all-time site records were also set in Victoria on 7 February, including Melbourne (154 years of record), where the temperature reached 46.4°C, far exceeding it’s previous all-time record of  45.6°C set on Black Friday (13 January) 1939. It was also a full 3.2°C above the previous February record, set in 1983. Three of Melbourne’s five hottest days have now occurred during this event. Geelong (47.4°C) and Wilsons Promontory (42.0°C) were among long-term sites which broke all-time records which had been set only the previous week. In total, of the 31 currently open sites in Victoria with 30 years or more of data which reported on 7 February, 21 set all-time records, five set February records, and only five failed to set records at all. 7 Record high temperatures for February were set over 87 per cent of Victoria.

The extreme heat on 7 February also affected eastern South Australia and the southern fringe of New South Wales. In South Australia, Renmark (48.2°C) set a February record for South Australia; this was also the highest temperature ever recorded in South Australia outside the pastoral districts or the Eyre Peninsula. Port Augusta (48.1°C) and Whyalla (48.0°C) also exceeded the previous South Australian record. No state records were set in New South Wales, where the highest temperature

was 46.8°C at Menindee, but all-time records were set at a few locations in the state’s south, with Wagga Wagga Airport (45.2°C) exceeding 45°C for the first time. This part of the heatwave did not penetrate south to impact on Tasmania, as occurred during the first acute stage.

The heatwave largely ended on 8 February, as a cool change crossed the south-east, although temperatures remained very high (albeit mostly slightly lower than the previous day) in New South Wales and the far north-east of Victoria.

As the most extreme heat in this part of the event only lasted for one or two days, very high overnight temperatures were not as much of a feature of this period as they were in the previous week, but there were still some high overnight minima recorded, including 33.7°C at Roxby Downs on 7 February, the second-highest on record for February in South Australia.

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The duration of the heatwave

In addition to its peak intensity, the 2009 heatwave was also notable for its duration. The 1939 heatwave was similarly prolonged in many inland areas, but sea-breezes and weak changes brought temporary relief to coastal areas, a feature which was absent in 2009 during the heatwave’s first week. (In 1939, Melbourne had three days above 43°C between 8 and 13 January, but there were interspersed with days in the 20s and low 30s, and there was no night in the period warmer than 18°C). At Adelaide and Melbourne, the event most directly comparable with the 2009 heatwave as that of January 1908, which had lower peak temperatures but set records in both locations for consecutive days above 40°C. Over the five days 27-31 January 2009, maximum temperatures were 12-15°C above normal over much of Victoria and southern South Australia. 

Both Adelaide and Melbourne set records for the most consecutive days above 43°C. Adelaide’s temperatures were at this level on each of the four days 27-30 January, and Melbourne’s for three days from 28-30 January, breaking the previous records of two at both locations. Adelaide also equalled its 1908 record with six consecutive days above 40°C, while Melbourne’s three consecutive days above 40°C was the first time this had occurred since 1959, and the seventh time in history. Adelaide ultimately had nine consecutive days above 35°C; after never having experienced more than eight consecutive days above 35°C before March 2008, it has now happened twice within twelve months.

In most inland areas the number of consecutive days above 40°C has not (yet) reached the levels set in 1939, but there were a number of exceptions. At Mildura, where maximum temperatures remained above 40°C throughout the heatwave, 12 consecutive days above 40°C occurred, the longest such sequence ever recorded at a Victorian station, while Broken Hill’s 12-day sequence was also a record. Nhill’s six consecutive days above that level set a new record, while Bendigo and Rutherglen both experienced five consecutive days above 40°C, setting a record at the former and equalling it at the latter. Nuriootpa (SA) and Sale (Victoria) also set records for the most consecutive days above 40°C. Records have also been set for consecutive days above more extreme thresholds at numerous inland locations, including Kerang, Deniliquin, Snowtown and Nhill, whilst in southern New South Wales, Deniliquin and Wagga Wagga both set records for consecutive days above 37.8°C (100°F). A notable record for prolonged heat was also set at Launceston Airport, where there were three consecutive days above 37°C in a location which had never previously experienced consecutive days above 35°C. 

The prolonged nature of the heatwave, and in coastal areas the replacement of a very hot and dry air mass with a warm, humid one, has also led to many records being set or approached for consecutive days with minimum temperatures above thresholds. Melbourne (six consecutive nights above 20°C) equalled its record set during the 1908 heatwave, while Adelaide (six consecutive nights above 25°C) fell just short. At Mildura a record was set with seven consecutive nights above 24°C, while an indication of the depth of the warm air was that Cabramurra in the Snowy Mountains (elevation 1 482 m) remained above 19°C for four days, having never done so for more than two days previously. (Cabramurra also equalled its all-time record high with 32.0°C on 30 January, while further south Mount Baw Baw (1 561 m) reached 30°C for the first time on record with 30.9°C on the same day, before surpassing it with 31.5°C on 7 February). Further inland, Woomera experienced a record 11 consecutive nights above 25°C.

The dry conditions before and during the heatwave

The heatwave, as would be expected, was accompanied by very dry conditions, with only isolated thunderstorms occurring during the period. Conditions were also very dry in the weeks leading up to the event, especially in Victoria and South Australia.

Melbourne had no measurable rain from 4 January to 7 February, the equal second-longest dry spell on record for the city (35 days). This approaches the record of 40 days set in 1954-55. Melbourne (0.8 mm) had its second-driest January on record, and with only 2.2 mm to 8 February has now experienced its driest start to a year on record. A number of locations around Melbourne (including Preston and Toorourrong Reservoir, near Whittlesea), as well as Ballarat, set new January records for rainfall. Many stations in Victoria north and west of Melbourne, and in South Australia and southern New South Wales, had no rain in January, including Port Pirie, Clare, Adelaide Airport, Renmark and Keith (SA), Swan Hill, Nhill, Stawell, Bendigo, Yarrawonga, Heathcote and Maryborough (Victoria) and Deniliquin (NSW). Most of these locations have experienced at least one rainless January previously. 

These dry conditions have further reinforced very long-term rainfall deficits in much of south-eastern Australia, particularly Victoria (see Special Climate Statement 16). The most acute long-term deficits, relative to previous records, have been in the area immediately north-east and east of Melbourne. Adelaide and Melbourne both experienced several days of daytime temperatures exceeding 40ºC. Adelaide experienced six days above 40ºC, which equals the previous record run of six days exceeding 40°C recorded in January 1908, with a near-record maximum of 45.7°C on 28 January 2009. Melbourne experienced three days in excess of 43ºC for the first time since 1959: 45.1°C on 30 January (the second highest temperature ever recorded in Melbourne, behind the 45.6°C recorded on 13 January 1939); 44.3°C on 29 January and 43.4°C on 28 January. Melbourne's most sustained heatwave occurred in January 1908 when temperatures reached 39.9°C, 42.8°, 44.2°C, 40.0°C, 41.1°C and 42.7°C on 15, 16, 17, 18, 19 and 20 January 2009, respectively.

(Source: Bureau of Meteorology Special Climate Statement 17 (4 February 2009, updated 9 February 2009)

The heat wave is reported to have caused some 37 deaths, mostly of elderly people. Thousands were treated for heat exhaustion.

Power blackouts hit hundreds of thousands of households in South Australia and Victoria. Temperatures buckled rail lines and prompted the Bureau of Meteorology to issue fire warnings for bush lands and parts of New South Wales, South Australia, Tasmania and Victoria. Wildfires destroyed scores of houses and the authorities in South Australia imposed a ban on the lighting of fires anywhere in the state. Melbourne beaches were abandoned as the sand was to hot for bathers to walk on.

Bureau of Meteorology

Bureau of Meteorology media releases

More heat for southern NSW but relief in sight

Heatwave sets records across southeast Australia

 

Weather conditions are the result of extremely complex interactions, and one particular event, such as this heatwave in Australia, cannot be attributed to one specific cause. However, according to the IPCC Fourth Assessment Report, it is very likely that hot extremes, heat waves and heavy precipitation events will continue to become more frequent as a result of climate change.

 

Tragic aftermath

In the wake of this historic heatwave and long-lasting drought conditions, another, more tragic record was set: wildfires caused the death of at least 181 people in the state of Victoria, many of whom were burned in their cars as they attempted to flee the flames. More than 900 homes were destroyed, 5 000 people left homeless and 350 000 hectares ravanges by the blazes). Some towns were almost completely destroyed (reports of 11 February).

Fire is a regular occurrence in the forests and grasslands of south-eastern Australia. In the hot, dry summer months, vegetation dries out and lightning triggers many natural wildfires. However, in the past decade, the area has experienced several severe droughts. In late January and early February, this year, parts of South Australia, Victoria, and New South Wales were also paralysed by the heatwave and conditions were prime for devastating fires, some of which appear to have been started by lighting and others, according to news reports, by arson. The event was the worst fire disaster in Australia’s history. The previous worst fire was on 16 February 1983, when 75 people died—the day that became known as Ash Wednesday.

 

satellite image  
30 January 2009: some 5 500 hectares had burned and at least 10 homes had been destroyed (NASA)
 

 

satellite   satellite image
9 February 2009: out-of-control fires raced into small communities and towns in Victoria (NASA)

From heat wave to floods

In contrast to the heat wave conditions experienced in January/February, the Bureau of Meteorology alerted the public on 13 February to a developing weather system that would bring flooding to parts of northern New South Wales this weekend.

Media release

 

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