"Why go to the trouble of subtracting out all the difficult to measure factors from dam levels when you can go to the source data, rainfall."
Precisely - and as the records show, there hasn't been much rain around.
There are two parts of Australia which have undergone severe decreases in rainfall since the 1970s - southern Western Australia and Victoria.
To quote from BOM's Special Climate Statement 9
"The decade from October 1996 to September 2006 has been a notably dry one in large parts of
southern and eastern Australia. Whilst much of tropical and central Australia has seen wet
conditions through most of the last ten years, for many parts of the south 1996 was the last year
with significantly above-average rainfall.
The most extreme rainfall anomalies have been in the area around Melbourne, where falls during
the last 10 years have widely been about 20% below the long-term average, and 10% below those
of any other 10-year period in recorded history. Other areas where rainfall over the last 10 years has
been the lowest on record are parts of western Victoria and adjoining south-eastern South Australia,
parts of eastern Tasmania, the area around Perth in Western Australia, and a few locations in the
Darling Downs and Burnett regions of south-eastern Queensland.
October 1996 is taken as the starting point for this statement, as September 1996 was the last in a
sequence of months with above-average rainfall in most of Victoria, as well as the end of the main
1996 rainfall season in south-west Western Australia, which preceded a run of eight successive
drier-than-average years in Perth. In New South Wales and Queensland, the downturn in rainfall
has generally been a more recent phenomenon, generally starting in 2000 near the east coast and
2001 further inland. It is noteworthy that in some of these parts the last 5-7 years have been dry
enough as to register on the 10-year deficiency analysis."
And that was in 2006 - the last 4 years have been no better. So make that a 14 year drought.