The long drought affecting southern Australia is officially the worst on record.
Bureau of Meteorology head of climate analysis David Jones said the 12-year drought that was devastating southwest Western Australia, southeast South Australia, Victoria and northern Tasmania was "very severe and without historical precedent".
Drought has gripped the Murray-Darling Basin since late 2001. It has worsened this year, as rainfall totals for the past three years have set record lows in many regions, including many critical to the Murray River.
Dr Jones said the rainfall figures were similar to the severe drought that lasted from 1939 to 1945, and the Federation drought, which ran from 1895 to 1903.
"Those three droughts, in terms of rainfall, are comparable," he said. "But this drought is a lot hotter than those two previous droughts. And those two droughts finished, whereas this one is continuing."
He said temperatures were about 1C hotter than the previous droughts.
"That is substantially hotter, and that one degree is a global warming signal," he said.
Dr Jones said the data suggested that for every degree of warming, there was a 15 per cent decline in run-off, or river flow, in the Murray-Darling Basin.
Inflows into the Murray system have been critically low, with new records continuing to be set. Inflows in the two years to the end of August were just half the previous record low, set in 1943 to 1945. Storages in the Murray Darling are now at 28 per cent.
The Australian Alps, in north-eastern Victoria and southern NSW, have recorded their lowest three-year rainfall on record. This area is critical to the Murray River. It covers less than 1.5 per cent of the catchment, but on average provides 39 per cent of the water flowing down the Murray River.
Dr Jones said the rainfall deficiencies for Victoria were the largest on record, with the state effectively missing out on two years of rainfall over the past 12 years.
"Across Victoria as a whole, if you add up how much rainfall has been missed in 12 years, it is now up around 1300mm or 4ft of rainfall -- a very, very large rainfall deficit," he said.
The most dramatic impact has been on Melbourne, which has just recorded its driest September on record.
"If one looks at the history of data we have for Melbourne, we have rainfall records going 150 years," Dr Jones said. "We simply have not seen anything like what we currently have, not even close."
He said similar drying patterns had been observed in the Mediterranean, and the southwest US. "There are currently some very severe droughts in those regions, and also substantial rainfall declines," he said.
It has been a different experience across northern Australia, which has been experiencing well above average rainfall.