On Monday I posted a graph of rainfall history and suggested that it indicated south east Queensland was not experiencing the worst drought in 100 years – that the current dry spell is not unusual in the scheme of things.
I was surprised how many comments in the thread following the post, and also in the many emails I received, were supportive of the notion that this is a worst drought ever.
Some argued that I didn’t understand definitions of drought and that a drought could simply be a result of too many people squashed into a region without the infrastructure to supply adequate water. Comment was also made that it would be interesting to see the rainfall history for the catchment averaged over 10 years.
Warwick Hughes has sent me the following graph, showing the rainfall history averaged over 10 years:
Mr Beattie has been reported in the Courier Mail stating that:
“Rainfall in the region has been well below average for the past six years and in fact it is the worst 10-year period in history,” he said. “It has been dry after dry, year after year, which has led to major storage deficits in our dams.”
Looking at the above graph Beattie may be technically correct, we may have had the worst 10-year period in recorded history, and those who want to define drought based on ‘supply’ rather than ‘rainfall’ may also be correct because we have never had so many people living in south east Queensland and probably never as many trees growing in the catchment.
But the above graph, and the graph posted on Monday, does indicate that south east Queensland has experienced comparative periods of low rainfall during the 1920s and 1940s. The current dry period is not unusual in the scheme of things.
My point is that: If we can not reconcile ourselves with our history, how can we hope to prepare for the future? It is important we understand what is special about this drought.
If we could perhaps start to acnowledge that rainfall has not been exceptionally low, we might, for example, be able to more clearly focus on other variables, including population.
There is also the issue of tree cover. A heavily timbered catchment generally produces less runoff. Page 7 of yesterday’s The Land reports Malcolm Turnbull, federal parliamentary secretary for water, explaining that the West Australian Water Corporation is thinning catchment forestry to increase run off by 6,000 megalitres a year. Mr Turnbull said the method could deliver “new water” at about 20c/kilolitre – far cheaper than piping or desalination.
I am not necessarily advocating tree clearing in the Wivenhoe catchment, but rather my issue is that here in Queensland, we tend to invoke ‘exceptional circumstances’ whenever there is a flood or a drought rather than taking a more evidence-based, and dare I suggest, more responsible approach.
Jennifer Marohasy BSc PhD has worked in industry and government. She is currently researching a novel technique for long-range weather forecasting funded by the B. Macfie Family Foundation.