Australia has experienced a range of weather and climate extremes through 2015. From record heat in spring to the most substantial low-level snowfalls in 20 years, there has been no shortage of significant events.
The year started with a wetter-than-average January in many areas and near-average temperatures nationally. February temperatures were warmer than average across large parts of Australia, resulting in the second warmest February on record, behind 1983. With the early end to the monsoon in the north, unusually warm conditions persisted into autumn. The start of March saw large areas of the interior record an exceptionally long period with temperatures well above average and there was a broadening of multi-year rainfall deficiencies across Queensland.
In May, the Bureau of Meteorology declared that an El Niño had established in the Pacific Ocean. Following this, much of Australia saw a dry winter with above-average temperatures, except in parts of the southeast where cooler-than-average temperatures were experienced into early spring. Frost was a frequent occurrence and low-level snow fell widely in eastern Australia during July and August. In Tasmania, the low-level snow was the most significant since 1986 and in New South Wales and southeast Queensland the most significant since 1984.
As often happens during El Niño years, hot and dry conditions became firmly established during spring — translating into a difficult end to the southern cropping season. Early October saw an exceptional early-season heat event which brought summer-like temperatures to southern Australia. In Melbourne, the AFL Grand Final was played in conditions more typical of a Boxing Day Test Match. The month as a whole was exceptionally warm, having the largest national temperature anomaly recorded for Australia in any month since 1910.
In terms of severe weather, spring and summer are also the most significant periods of the year for Australia with increased risk for bushfire, tropical cyclones, heatwaves, and more frequent severe thunderstorms. Already this season, there have been bushfires in the southern States, and severe thunderstorms have affected several regions, with associated structural damage, damaging hail and flash flooding. Monitoring significant weather is vital in understanding the risks facing the Australian public and to help emergency services plan for the challenges of the severe weather season.
Looking ahead – how might 2015 end?
With the year coming to an end, meaningful estimates of how the 2015 national average annual temperature might rank can be made. With the firmly established El Niño in the Pacific Ocean, warm conditions will most likely persist across the globe over the next few months. For Australia, the year-to-date (January to November 2015) and the 12-month running mean temperature ending in November 2015 are the sixth highest and fifth highest on record (+0.81 °C and +0.82 °C, respectively). These values mean that while 2015 will be warmer than average, we can be quite certain that the year will not be Australia’s warmest on record—which occurred in 2013 with a +1.2 °C anomaly.
In estimating what the final Australian temperature for 2015 might be, we consider the December monthly Climate outlook (issued 19 November), and the strong El Niño; both of which favour continued above-average Australian temperatures (relative to 1961–1990). This outlook indicated a December temperature anomaly of around +1.0 °C, which would rank the national mean temperature anomaly for 2015 as fifth warmest on record.
Looking at possible outcomes based on historical scenarios, the average from the reference period (1961–1990) for December results in an annual temperature anomaly for 2015 of +0.75 °C; the sixth-warmest year on record.
There is little prospect that the year will end cooler than this outcome since large parts of Australia have already experienced well above average temperatures during the first half of December 2015.
Scenarios based on recent climate averages may be more realistic for predicting the likely 2015 annual temperature. If 2015 ends with the average December temperatures from this century, Australia would see its sixth-warmest year on record. Taking the coldest and warmest Decembers from the entire historical record results in 2015 annual mean temperature anomalies of +0.61 °C and +0.89 °C, respectively ranking ninth and fourth.
|Projected annual anomaly
|Warmest November to December on record
(occurred in 1990)
|Persistence of January to October 2015 anomaly||+0.81||+0.81||6|
|Average anomaly since 2000 for November and December||+0.29||+0.77||6|
|1981–2010 November to December average||+0.09||+0.75||6|
|1961–1990 November to December average||0.00||+0.75||6|
|Coldest November to December on record
(occurred in 1916)
|The Bureau’s dynamical model forecast for December 2015||+0.97||+0.83||5|
Based on temperatures already experienced across Australia through December, we estimate that the year is likely to sit in the top six warmest years on record and could end in the top five.
As described in the table above and graph below, these scenarios provide a guide to the upper and lower bounds of likely outcomes for this year’s mean temperature anomaly. The Bureau will provide a more complete description of the 2015 climate when data are available in early January 2016.
Areas affected by drought
Much of eastern Australia has seen below-average rainfall since the last La Niña concluded in autumn 2012. Significant rainfall deficiencies are present across a range of timescales, particularly in southwest Western Australia, southeast South Australia, much of Victoria and Tasmania and most of Queensland and the Northern Territory. Prolonged drought conditions have affected inland Queensland and western Victoria for the past three years, with some areas having their lowest rainfall since 1900.
Rainfall during the southern 2015 growing season, which spans April to November (Figure 4a), has been below to very much below average for the season in most of Victoria, southeastern South Australia, Tasmania, and across most of the South West Land Division in Western Australia. For the three months September to November (Figure 4b) rainfall has been below average across most of Victoria, Tasmania, southeast and northern parts of South Australia, inland Queensland, through much of the Northern Territory and the west coast of Western Australia. This particularly dry end to the southern growing season, along with some record-high temperatures, has exacerbated existing drought conditions present in western Victoria and adjacent areas across the border in South Australia, and is consistent with a long term trend of rainfall decline during the southern wet season in these areas.
How have global temperatures been tracking?
The US National Oceanic and Atmospheric Administration (NOAA) has reported that the 2015 January to October global temperature is the warmest such period on record (with global records beginning in 1880). Eight of the ten months in this year to-date have been the warmest on record for that respective month, while January 2015 was the second warmest and April 2015 the third warmest. October 2015 marks the sixth month in a row that the global monthly mean temperature has been broken. Both September and October were also the warmest on record, in terms of anomalies, for any month amongst all 1630 months in the observational record. These records have been driven by the strong El Niño and record-warm sea surface temperatures across large parts of the Pacific and Indian oceans.
While some El Niño indicators are now showing signs of easing, but are likely to persist well into 2016, global surface temperatures indicate it is likely that 2015 will be the globe’s warmest year in the instrumental record. The previous warmest was set in 2014.
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