Worst Drought in 100 Years - or Not? (Updated August 22, 2006)

We are in the middle of an election in Queensland, Australia.

My local member has just sent me a glossy brochure stating that:

"Queensland is experiencing the worst drought in 100 years ...no other government in our history has faced a challenge of this enormity."

The Premier Peter Beattie has being repeating the same message for some time.

So how bad is it - really?

The catchment with Brisbane's dams is reportly the most severely affected.
Warwick Hughes has constructed the following graph from the rainfall record for the Wivenhoe catchment -- that's the catchment with the dams:

So there is really nothing unprecedented about the current dry spell? Could the Bureau of Meteorology please correct the graph, or correct the Premier?

Update 22 August

Simon commented (see following thread) that the above graph looks different to the graph posted by Warwick at his site. Following is the graph posted by Warwick:

I made the error of assuming the graph Warwick sent me on the weekend was the same as the one he had posted at his blog. There are slightly differences after 1990, because as Warwick explains in the note at his website, "rainfall data is less than perfect, many stations close and an alternative has to be opened at another site, recordings can start then stop, there can be gaps in the data".

In the graph I posted, Warwick had used values from neighbouring stations to see what a more complete record for the catchment looked like.

He has sent me the following comment tonight:

"If I can obtain a more complete catchment dataset I might spend a long day trying to correct these.

The Bureau of Meteorology and water utility have had years to publish a graph of catchment rain history if they wished to do so.

Clearly, it must not be perceived to be in their interests or they would have done so.

Likewise, I have never seen catchment rain history charts made by a water utility or the BoM for Perth, Sydney or Melbourne but maybe there are some I have not spotted.

Why is this when water supply issues are controversial in all our cities and all our dam water originates as rain.

I see the issue of the 2002 drought being raised and I show from the Australia wide Bureau of Meteorology high quality rain data that in 2002 there was a Great West Queensland drought but nothing nationwide to match the Federation drought.

...With respect to the claims of "worst drought in a whatever", the criterion I was talking about was the definitions of serious and severe drought as on the Bureau of Meteorology website and as expressed in their maps with shades of pink to red. I have a small area of their latest 3 year map shown on my Brisbane page. Now I do not know what result you would get if that Bureau of Meteorology 36 month drought map series could be rolled back through 2000.

But do we expect policymakers to be making such definitive statements about data that is far from black and white and when the result is probably so line ball?"

When I look at the second graph I see regular wet periods with yearly averages around 1200mm (once as high as 1400mm) and there have also been regular dry periods with yearly averages around the 600mm (once as low as perhaps 450mm). We are currently in one of the dry periods with yearly averages in the 700-800mm range.