While there's still a week or two to go in the year—and as severe tropical cyclone Owen and heavy rain in Victoria and Tasmania have shown—a lot can happen in a week, 2018 is on track to be a very warm and dry year for Australia.
- One of the ten warmest years on record for Australia
- Days especially warm
- Rainfall likely to be somewhat below average overall
- Much of eastern Australia affected by drought
- Tropical cyclones contributed to above average rain to parts of the north and west
How is the year shaping up?
This year has been a warm and dry one for Australia as a whole.
It has been drier than average across Victoria, New South Wales, large areas of Queensland, eastern South Australia, parts of inland northern Australia, and along the west coast and southwest of Western Australia. Rainfall has been above average across parts of the tropical north and in a band extending from the Kimberley down through central and eastern Western Australia.
Turning to temperature, we expect 2018 will be in the ten warmest years on record for Australia.
Eight of Australia's ten warmest years have occurred between 2005 and 2017, and this year will mean only one of the ten warmest years occurred before 2005. This is in line with long-term trends resulting from anthropogenic climate change.
Days have been persistently warm though the year, and 2018's mean maximum temperature is likely to be amongst the five warmest values on record for Australia as a whole. Mean maximum temperatures have been warmer than average across nearly all of Australia, and all of the States and the Northern Territory are likely to come in amongst the ten warmest years on record.
Minimum temperatures have also been warmer than average across most of Australia, although mean minima are tracking cooler than average across the Kimberley in Western Australia.
Previous warm and dry years have often been associated with El Niño, but the tropical Pacific Ocean was in a neutral phase for most of 2018.
2018 commenced with a very weak La Niña active in the tropical Pacific Ocean, but this dissipated during the end of summer without having much effect on Australia. From winter onwards the tropical Pacific Ocean steadily warmed, reaching El Niño threshold temperatures by October. However, the atmosphere did not support and reinforce the oceanic pattern, so El Niño has not yet become established. This phenomena of El Niño-like conditions in the waters of the tropical Pacific Ocean, but an atmosphere which has not shown El Niño signals, is unusual but not without precedent.
On the other side of the continent, a positive Indian Ocean Dipole (IOD) was active between September and early December, and may have contributed to the dry conditions seen in the southeast.
In the absence of strong Pacific or Indian ocean climate drivers, local influences came into play. These included warmth in the Tasman Sea (which reached record-setting levels early in the year), stronger winter westerlies, and a southward shift of rain-bearing fronts.
Rainfall during the year
Parts of the country had a wet start to the year. Tropical systems, including cyclones Joyce and Kelvin, affected the Northern Territory and Western Australia in January and February, and brought flooding rains in parts of Queensland during March.
However, rainfall was generally below average outside of those areas, and from April to September was below average across most of Australia in each month.
September was an exceptionally dry month, especially across the southern mainland. Rainfall was the lowest on record for September both nationally, and for southern Australia (those areas south of 26°S). Total April to September rainfall was the fourth-lowest on record for southern Australia.
Marked rainfall deficiencies were in place throughout the year in very large areas of eastern Australia, and came on the back of ongoing deficiencies at longer timescales (see Special Climate Statement An abnormally dry period in eastern Australia).
While above average rainfall in some areas during October, November, and December have helped raise soil moisture and lessen some impacts of the long dry, regular rainfall over a period of several months would typically be required to remove the very large rainfall deficiencies which have developed since early 2017.
Widespread warmth throughout the year
Low rainfall has also been accompanied by very high daytime temperatures so far this year.
Maximum temperatures were above average for each month of the year, and are likely to also be above average for December. Throughout the year maxima were above average across most of Australia. Exceptions were cooler than average days in the west during January and February, and also parts of the Top End of the Northern Territory in January, northwestern Queensland during March, and parts of Western Australia during August and November.
April was exceptionally warm, with persistent summer-like heat setting many records across southern Australia during the first half of the month. Mean maxima for April were either the highest, or second-highest on record for April for New South Wales, Victoria, South Australia, Western Australia, and the Northern Territory.
A heatwave in late November to early December saw record-breaking temperatures near the north tropical and central coasts of Queensland, with extensive and significant fires occurring across eastern Queensland.
Month after month of warm days, combined with the very low rainfall, contributed to elevated fire danger, and a prolonged fire season. Forest Fire Danger Index (FFDI) levels remained high well into autumn, and the bushfire season started again in late winter in New South Wales and Victoria, much earlier than usual.
Nights were also warmer than average across much of the country for much of the year. The cooler months however did see below average minima across large areas during May to September, which is a common feature during drought years.
September saw particularly cool nights, with mean minima the coolest on record for the month over a large area spanning central-northern and northwestern Victoria and northern agricultural districts of South Australia. Significant frosts around mid-month caused crop losses in parts of the grain-growing regions of both States.
What about the rest of the world?
The World Meteorological Organization (WMO) issued its preliminary statement on the climate of 2018 on 26 November.
For the globe as a whole, 2018 is likely to be the fourth-warmest year on record, continuing the recent pattern of very warm years.
Each of 2015, 2016 and 2017 also broke the pre-2015 record for warmest year. All of the ten warmest years have occurred between 1998 and the present. Global temperatures have increased by approximately 1.1 °C since the pre-industrial period, and 1978 was the last time the global annual mean temperature was below the 1961–1990 average.
The global mean temperature is estimated using observational datasets from the UK Met Office Hadley Centre (HadCRUT4), the US National Oceanic and Atmospheric Administration (NOAAGlobalTemp), the US Goddard Institute of Space Studies (GISTEMP); and two reanalysis datasets from European Centre for Medium-Range Weather Forecasts and Japan Meteorological Agency (ERA-Interim and JRA-55).