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 is a critical thinker with expertise in the scientific method.
Excellent stuff Jennifer.
Evidenced based policy making is thankfully getting more academic time as a part of public policy and management courses.
The new Carnegie Mellon University in Adelaide gives it emphasis.
Not so long ago it was called doing your home work.
Though I still question Warwick’s data handling abilities (now we have a third graph, this one with 10 year smoothing (how is this calculated?), I suppose at least most of the points still look the same). The plot still shows that we have had six consecutive years of below 800 mm rainfall for the first time on record. It’s the fact that we have had consecutive years of low rainfall that is the worry. Dry years are a problem because:
1) Water Consumption goes up due to people watering gardens etc;
2) Evaporation rates go up; and
3) There’s no rain to keep up with even normal water use.
Now we have had six of these years in a row, something without precedent, but do we have to do something about it?
If you believe that this lack of rain is due to natural variability then the answer would be – do nothing. Why – because this is a once in at a least hundred year event and rain is just around the corner. We sould just grin and bear it because increasing dam capacity, water recycling and building desal plants are wastes of money because, chances are, it will be at least 100 years before we’d see another dry period like this.
Now if you believe in global warming and that our future climate will be more erratic with more low and high rainfall years then the answer would be that we should invest in ways to insulate us against this – dam capacity, water recycling, etc.
Simon – just on the issue of “we’ve had our 1 in 100 drought – so that’s it for another 100 years”. If we assume there is no teleconnection or linkage in the pattern and each year is an independent throw of the dice then it doesn’t follow it will be 100 years. Same with Federal drought aid for 1 in 20. Doesn’t mean droughts will be 20 years apart nicely. Problem is what if you have a century’s worth of 1 in 20 in a decade !!
Of course if you want to link the years as a climate mechanism sequence or invoke climate change dismiss the above. I’m just pointing out that people don’t have a good idea what 1 in 20 or 1 in 100 actually means. That’s why better to say percentile 5 or percentile 1. It’s less ambiguous.
Luke is right about percentiles, that’s the criterion the use in these discussions. But getting back to the rather novel concept of planning (as far as the Qld government is concerned). If one had looked at this graph as it was some 8 years ago when the current government was elected, what would the message be? That its not at all uncommon for Wivenhoe catchment to have pretty long dry periods. And while spouting on about how many more millions of people will soon live in SE Qld, what precisely did the government do to plan for the future. Precisely nothing.
It seems to me like this. By definition, we should expect a 1/2 probability of annual rainfall falling below, or above the long term median. The probability of six years in succession below the median (if that is what happened) is 1/2 raised to the sixth power, ain’t it? Which is 1/32. So we might expect such a run about (careful now, not exactly) three times a century, over a very long run. Is that very rare? Luke may care to bring his Pascalian skills to bear. Who will write to Mr Beatty?
Davey – yep I think I agree with your maths given a few provisos.
(1) the years are independent throws of the dice
(2) We forget about non-independent things like antecedent catchment conditions, tree cover thickening, El Nino, La Nina, Interdecadal Pacific Oscillations, anthropogenic induced climate change, and the fact that the north Qld coral core records say we only have a small sample of the total background variability.
If you overlay the dam drawdown for the current drought say starting Feb 2000 till current over the simulated drawdown Federation period say 1897 till mid 1903 you get almost identical behaviour until May-June when the Federation drought would have started to climb already to reach 60% by Xmas. So we’d be out of drought and hosing those driveways again ! (hope not).
(3) if the years are independent the probability of each new year being above the median is still 1/2
So given this is below that it is worst on record. So we have worst on record and we’re all still alive, showering albeit with stuffed nurseries and dry gardens. So I still believe it’s the worst on the numbers – but this is a sort of pub argumnet really.
But would punters let you build a dam in a good season when hospitals, roads, and education need so mnay dollars spent on them. What a waste we’d all say. So this is the wakeup we had to have. Will do us good.
Everyone including politicians is hopeless at planning for and managing drought. Why totally blame them – none of us are much better.
But if you look at the points I have listed under (2) above – there are very good reasons to now undertake a state of the art risk assessment. I am supportive of doing “the works” – more dams, conservation, rainwater tanks, desal, recycling for industry, and interlinked systems via pipelines. We deserve it – but we also need to pay for it.
My major concern is that we need to be careful about the lungfish, Mary Cod and Mary River Turtle. Need some great ecologists like Russell and Stewie to look after our interests on these issues.
The other difference is that if you had Wivenhoe Dam in 1902 it wuld still be full as the population was zippo in comparison. Not that that is relevant for simulated comparison of worst !
But Davey a rational analysis would suggest the scare we’re having would have occurred before in 1902 – except this is scientifically demonstratable to be the worst on our rainfall records. It’s passed that by a few months. But we know much more than that from our coral cores don’t we?
Then again, looking at Warwick’s graph, I can spot only three occasions, over the past century, when there have been runs of five consecutive years above, or below my guess at the median. If my beady old eyes do not deceive me (they well may), two above, and one below. So Queenslanders have been very lucky to avoid more such runs below the median over the past century. This is due to superb management by Sir Jo Bjelke-Petersen. I can now reveal that I was a member of a top secret team, which carried out Operation Kingaroy. We fired crushed peanuts into cumulus clouds, above a certain farm. Sorry Peter, you are a likeable chap, and doing much that is good I am sure, but you can’t compete with the old master. Don’t you worry about a thing, by Golly.
Wait one Luke,
Isn’t 1/2 to the sixth power 1/64? Shame on you! Well anyway, that’s about once or twice a century. Must have happened before whitefella came.
Correct – I agreed on the the method but didn’t check the arithmetic (just like in sckool!). Sackcloth and salt tomorrow. And I agree it’s a shoot-out between 1902 and now. If we have rainfall records (depends on area – Warwick will know of course) from 1890 till now that’s about 116 years (but don’t trust my arithemtic!).
Luke!
Being late in the day, I ignore your spelling as well, not only your sic.”arithemtic”!.
Sleep well.
Seriously though, we just do not know for sure, do we?
Cheers
Sorry guys, this is all moot because that graph is only for the Wivenhoe catchment. The city itself has had no drought as the monthly totals for the 12 months to April 2006 at Logan on the city south shows.
Rainfall Logan City per BOM
L05/06 Mean
May 2005 57.9 130.9
June 239.4 53.8
July 40.4 38.6
August 11.1 48.6
September 12.3 45.8
October 116.0 55.2
November 138.1 105.4
December 129.0 128.3
January 243.4 104.0
February 83.1 144.0
March 117.9 131.9
April 56.6 71.7
totals 1245.2 1058.0
percentage of mean 117.7%
Clearly, the “continuous dry period” has not been uniform and has been been neither continuous nor dry.
But, of course, it is no longer illegal to even lie to Parliament, let alone lie to the voters of Queensland.
Zounds Sir Ian… do you mean statistics can lie?
Ian – bolsh – don’t run your politics with the maths.
Logan ain’t Wivenhoe catchment.
Does Brisbane drink lots of Logan catchment water
Rainfall does not equal catchment runoff
If Logan rainfall and implied runoff is so good one wonders why Maroon isn’t overflowing?.
The runoff modelling says it’s the worst period on record for surface water generation in the Wivenhoe catchment.
That’s that and get over it.
If you want to argue for rain tanks or any other solution – fine – but that’s another argument.
Anyway Ian – let’s move the extra trees consuming water discussion which is not nailed down.
Where do we have dense regrowth forests in SEQ – what parts of the catchment.
Looking at Maroon for example – the catchment has been burned in recent years from memory, slopes are steep, soils are shallow. Dam is low.
Does the Vertessy proposition hold up everywhere. I think Tom McMahon has also demonstrated the effect on the Comet systems. But in SEQ most of the trees are on steep slopes that nobody wants for agriculture (i.e. national parks and reserves.) Do we have any real data to say these systems are changing?
And on the koalas – how did they evolve without us whitefellas ?
What this graph appears to show is that the Premier is technically correct, but specifically wrong. What the “worst in 100 years” is supposed to prove is that no-one could have foreseen similiar circumstances and planned for them.
The graph shows quite clearly that there have been equivalent periods, perhaps not quite as bad, but only by a small fraction.
I’m not a big fan of the National Party, but one thing they do seem to understand is water infrastructure. In 1989 both the Liberal and Labor parties opposed the Wolfdene dam, and when it came to power, Labor scrapped it.
It transpired during the week that last time the Coalition was in government it actually planned to build four dams, a plan which it has now dusted off as an election promise.
So to suggest as the Premier does – a suggestion with which you agree – that this drought is just a bit of bad luck and no-one would, or could, have done anything about it is wrong, on the basis of history and fact.
If we had more water storage then it wouldn’t matter that the dams were only 30 percent full.
On a MACRO-Scale,
Southeast Queensland’s problem is not dissimilar to that which Sydney started experiencing a few years before the major-drought of 2001-05 started to creepup on it ; both big and getting-bigger fast Cities, they both lie downwind of a range of hills, or ‘mountains’, being the Border Range and the Great Dividing range respectively; both cities put-out/exhaust huge amounts of hot/heated air, day and night, creating major new air convection patterns, upwind, downwind, and at-altitude above the cities; both cities are located at the far-eastern seabord of a major dry continent; winds, erratic-freak winds, and the velocity of peak-wind occurrences are known to be rising or increasing – a FACT first reported nearly 2 decades ago, in the New Scientist magazine, based on a study-Research of equipment located around a representative range of large cities; the effect and impact of the rising-winds, much of which is/are getting-diverted ‘up and away’ from lower altitudes over large cities, implies that there IS NOW an enlarged ‘RAIN SHADOW Zone’ in behind the ranges that are set behind those big cities; in both cases, these same ranges are set-back some 100 kms; and it is ‘easy to see’ (for a retired mountaineer!) WHY ALL THIS IS Happening – to both cities at-once;
most observes do not take ‘the Big Picture’ into account – because they don not have the overview that comes from spending years ‘in the mountains’ themsleves, and learning to look at problems differently!
Thanking you, Keep Learning!
Joe A Friend, Author, Independent Scientist
& CRC-Director( http://www.camphorlaurel.com),Lismore.
Luke, all I concluded was, “Clearly, the “continuous dry period” has not been uniform and has been been neither continuous nor dry”. So what is “bolsh” about that?
Take a look at SLATS “land cover change in South East Qld 1988 to 1997 Table 9
Stanley River, % woody veg 1988 = 63.7%, % cleared from 1988-97 = 0.6%
Upper Brisbane, % woody veg 1988 = 43.8%, % cleared from 1988-97 = 0.2%
Monsildale Creek, % woody veg 1988 = 72.8%, % cleared from 1988-97 = 0.1%
Kilcoy Creeks, % woody veg 1988 = 53.7%, % cleared from 1988-97 = 0.0%
Cooyar Creek, % woody veg 1988 = 46.8%, % cleared from 1988-97 = 0.4%
Emu Creek, % woody veg 1988 = 43.0%, % cleared from 1988-97 = 0.1%
Maronghi & Ivory Creek, % woody veg 1988 = 36.8%, % cleared from 1988-97 = 0.0%
Cressbrook Creek, % woody veg 1988 = 54.4%, % cleared from 1988-97 = 0.1%
Brisbane East, % woody veg 1988 = 85.7%, % cleared from 1988-97 = 0.0%
From this we can see that forest management and mis-management is a highly relevant consideration in respect of Brisbane water yield.
I cant find the document presented to the RVMP committee but recall that approximately half of this vegetation is remnant while the other half is regrowth that has not yet been mapped as remnant. Much of the remnant has a large regrowth component.
Gidday Joe Friend,
Re your 28 August posting.
I wondered if you could share your Sydney data with us that backs your claim of ” major-drought of 2001-05″.
On Sydney there has been some work that suggest that the changing landscape is also responsible for increasing the violence of some storms, say two Macquarie University researchers who have spent more than a year using a supercomputer to model the impact that two centuries of clearing Sydney’s vegetation has had on severe weather.
http://www.smh.com.au/news/national/climate-surprise-over-storms/2005/10/23/1130006005899.html
Then there is the pollution blocks rainfall hypothesis guys that lead to cloud seeding.
http://www.aph.gov.au/house/house_news/magazine/ath18_cloudseeding.pdf
http://www.abc.net.au/news/newsitems/200608/s1710396.htm
http://www.news.com.au/couriermail/extras/blogs/water/2006/06/seed-clouds-part-2.html
Ian – Logan is not Brisbane – if you lived in Brisbane you would know that Brisbane and north are experiencing the drought – Logan, the Gold Coast and coastal northern NSW had some good rain last year but it didn’t reach Brisbane.
Also Joe – when you say CRC is that the Cooperative Research Centre for what exactly? and taking the bigger picture into account what about Melbourne and Perth?
Simon C, Strathpine, in the north also has a similar data set showing above average rainfall for more than 12 months last year. Mt Gravatt in the middle had a slightly below average year.
So no matter what spin you try on, the statement “we are in our worst..” is untrue because some of us are not.
And when we look at the monthly breakdowns there have been some very good seasons during the past decade. The point is, there has been an unusual but not rare sequence without very large rainfall events on which dams rely. The wildlife, in contrast, have had some good years during this time where a lower volume of rain has been spread out more evenly to maintain the nutritional value of leaf, bark and flower stocks.
A dam reliant urban community’s drought can be an arboreal mammal’s good season.
Yes Ian a dam reliant urban community’s drought can be an arboreal mammal’s good season. There’s a fair bit of grass out there waiting for the usual pyros to light it up. Cooler rainy weekend has taken the edge off. And yes areas near the coastal strip are having better rainfall. But the argument is for the Wivenhoe catchment. FOR HEAVENS SAKE !!! If you want to say that Brissos’ rainwater tanks might be OK on the coastal strip that’s another debate. How much of this can a Koala bear?
And was it you who wrote “Brissos go home” on the rocks at Byron Bay?
As it appears the houses have been built where the dams should have been, the whole plan for dams must be wrong.
Instead of building dams in rural areas, where the rain isn’t falling, the dams should be built in the urban areas where it is falling.
So you can build tin & plastic dams, [tanks], or you can resume a few thousand suburban houses & build dams.
It makes sense to me. As the dams are for the exclusive amenity of the urban population, surely the pain should de distributed in the same area.
Can you imagine the NIMBY scream if it happened. Suddenly the idea of new dams would become a whole lot less attractive.
Ian I’m going with the BOM and my disused lawn mower on this one – SE Queensland in general and Brisbane and north in particular are in drought.
Beattie isn’t “technically correct”, he’s “correct”. The fact that some others run a close second, doesn’t change the fact that this is indeed the worst drought in 100 years, just as he claimed.
The question of whether this is a bad draw from a stationary distribution or reflects a contribution from anthropogenic climate change can’t be settled by the kind of eyeballing that’s going on here.
Luke, as a person who can actually remember surfing the Pass without backpacker-rage, I can advise that I have not actually been to “the Bay” (as real locals call it) for a decade because it is all so very, very sad. And it is not so much the tourists that offend me but, rather, the “11 month locals” who think they own the place but invariably slip away to be replaced by another set of cliche’s before handing a feral minority a rented electoral mandate.
And as for Dams. Why is it that it is OK for us to drink overly expensive recycled sewerage but we cannot allow waterfront housing on the banks of our Dams? Nothing improves a dams catchment efficiency like urban development. Wivenhoe has over 500km of waterfront land which could take all the pressure off the coastal strip. At even modest rates of development and density it could produce value increases that could completely idiot-proof our hospital system, fix our roads and increase the supply of storm water to such an extent that no new dams would be needed.
But that would involve decision making by government that is not afflicted by asynergy. The collective intellect of what we’ve got is significantly dumber than the sum of the individual intellects involved.
And one more interesting stat. This years rainfall at Wivenhoe has been only 500mm or just over half of the annual average. Run-off from the catchment has been effectively zero but is normally about 5% of rainfall. Evaporation from the dam is about 2000mm.
So a houseboat floating on Wivenhoe over the past year would have saved four times more water than actually fell on it’s roof. Each square metre of houseboat roof, or deck, would deliver the same water volume as 40 square metres of catchment.
The median house size, if built on stilts in the dam, would collect all the water it needs from the roof and save enough water from evaporation to supply two more houses.
Ian – lets talk median not averages with rainfall. But yep happy with tanks and no dams if you can convince the electorate – good luck !
I’ll need a bigger shovel. And OK, if it will make you happy, Wivenhoe is in drought, possibly the worst for donks. But Maroon Dam is not anywhere near Logan Treatment works where the weather station is.