VICTORIA has posted its 12th hottest year in more than 100 years of records and experts are debating whether 2012 marked a return to normal dry conditions or a shift towards another drought.
For the year, Melbourne's rainfall of 602 millimetres was just below the long-run average of 650mm, the weather bureau said.
Statewide rainfall was below average for the 14th year of the past 16. The first half of the year saw 353mm land in the city's rain gauges, 44mm more than the average, before the trend reverted to a well-below average of 248mm for the rest of the year, down about 100mm from the norm.
''Historically the second half is much wetter than the first half,'' David Jones, manager of the weather bureau's climate monitoring and prediction unit, said. ''The dry in the second half was really significant.''
Statewide, Victoria posted its 12th hottest year in 103 years of records, with a mean of 14.54 degrees or 0.44 degrees above average. Ten of the 13 warmest years for the state have happened since 1990.
In the last four months of year, though, temperatures were almost 1 degree higher than average. Nationally, the period posted the highest average on record, and a new national high - beyond the record 40.17 degree average on December 21, 1972 - may be reached early next week as the blistering heatwave re-intensifies after a breather.
Several all-time records fell on Friday, including Hobart where mercury soared to 41.8 degrees. Adelaide sweltered in 45 degree heat, the fourth hottest day there since records began in 1887.
Climate experts say the past two years of relatively cool and wet conditions associated with a so-called La Nina climate pattern over the Pacific Ocean were a temporary break from the trend. Even the two La Nina years were the warmest on record for the climate pattern, suggesting there was no departure from the multi-decadal warming underway.
The debate now is whether conditions will revert to a more normal dry or a return of the drought conditions in southern Australia in the decade to 2007.
''There are indications we might be slipping back into the big dry of the 1990s up to 2007,'' said Will Steffen, a member of the Australian Climate Commission and executive director of the Australian National University's Climate Change Institute.
The weather bureau's Dr Jones said the drying trend appeared in the 1960s and early 1970s in Western Australia's south-west and spread east.
''It's very clear that the whole of southern Australia is experiencing a quite profound change in the seasonal cycle of rainfall,'' Dr Jones said.
In short, while La Ninas may bring the occasional wet summer, winter is a lot drier than in decades past.
Runoff into Melbourne's reservoirs is dwindling as soil moisture levels fall. The outlook offers more of the same, with predictions of a hotter and drier summer than average.
''Much of the runoff into Melbourne's dams comes during the cooler months of the year, and that rainfall has not returned to normal even during the La Nina years,'' Professor Steffen said.
''So I think there's a real concern about the risks to water supplies of Melbourne,'' he said. ''The Melbourne water supply operators need to be aware.''
The government has no plans to alter its ''zero gigalitre order'' for water from the Wonthaggi desalination plant, with the next decision not due until April.
''As in 2012, future water orders will be made with consideration given to recommendations and advice provided from Melbourne's water authorities,'' Water Minister Peter Walsh said.
''Melbourne's water storages are in very good shape heading into the warmer months at 80.5 per cent capacity. At the same time last year, storages were 66 per cent.''
Bruce Rhodes, manager of water resources at Melbourne Water, says his organisation is ''aware of the changes to rainfall and its impacts on catchment stream flow. With a return of warmer and drier conditions … we would expect water storage volumes to fall more than in recent years and this is being taken into account in our planning.''
The weather bureau's Dr Jones said southern Australia’s weather systems are shifting towards Antarctica, much as climate change models would suggest, although the general drying of the region is on the high end of forecasts.
"The current rate of drying is rather more rapid than most models would seem to predict,” he said.
While Victoria's temperatures have been trending higher, meteorologists say the numbers are more dramatic for record setting temperatures iover the last decade outside of the summer period.
Notable record highs for the state set in the last decade include 29.9 degrees in August, 37.4 degrees in September, 40.2 degrees in October, 45.8 degrees in November and 48.8 degrees in February.