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The Queensland floods

Posted on 12 January 2011 by John Cook

As the Queensland floods have now hit Brisbane, a number of people have emailed or posted comments enquiring about our well-being. Many thanks to everyone for their thoughts and concern. I'm happy to say the Cook family is safe and dry - we happen to be located in a relatively elevated area (not by design - extreme flooding was not even on my radar when we moved into the area). However, many nearby suburbs have not been so fortunate.

Ten minutes south-east from us, low-lying areas of Strathpine were evacuated yesterday. South Pine River has burst its banks and covers a large portion of the suburb:

Meanwhile, to the north-west of us, just down the road from our church, One Mile Creek has also burst its banks and blocked off the road:

Up to 40,000 homes are estimated to be affected by flooding over the next day, when the Brisbane River peaks at 3am tomorrow morning. But while the flood waters rise gradually here, incredible scenes were witnessed earlier this week in the town of Toowomba, 90 minutes west of Brisbane. The media are refering to it as an inland tsunami - a wall of water rushed through the town, dragging along cars, shipping containers and even houses. We heard accounts of entire homes being plucked off their foundations and carried by the waters, with people inside crying out for help. The tragedies this and other Queensland towns have endured are heartbreaking and the damage mindboggling.

When these kind of extreme events happen, people ask "Did global warming cause this flood?" as if the answer should be yes or no. It's more appropriate to ask does global warming have an effect on these types of events? The scientific evidence indicates yes. As temperatures have risen, we've observed more water vapour in the air. More water vapour leads to more extreme rain events. Over the last few decades, we've observed an increase in the number of extreme precipitation events. And we expect the number of extreme precipitation and flooding events to increase as global warming continues.

It's times like this that I can't help thinking of the words of NOAA scientist Deke Arndt, "Climate trains the boxer but weather throws the punches". Weather will always throw these random punches at us. Occasionally it gets in a lucky punch that knocks us off our feet. But what we're doing is training weather to throw harder punches at us and more often. That's what is being observed and that's what we expect to see more of in the future.

Anyone who wishes to help, you can Donate to the Queensland Government's flood relief appeal.

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Comments 51 to 84 out of 84:

  1. The SST records may have come from something like this source http://www.bom.gov.au/announcements/media_releases/climate/change/20110105.shtml showing a rise of from about -0.5 to 0.5 over a century.

    That fits nicely into figure 2 in http://home.badc.rl.ac.uk/mjuckes/mitrie_files/docs/mitrie_sediment_marine.pdf which shows a natural range of about -1 to +1 in the past 2000 years. Whether or not the current SSTs are AGW (or partly AGW), they are within the natural range.
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  2. #49 Michael Hauber at 12:15 PM on 13 January, 2011
    rainfall trends for Australia are uncertain

    No, they're not. Australia, as a whole is definitely getting wetter on a century scale.



    Average precipitation over the continent has increased since 1900 by some 20%. Of course it says nothing about the spatial and seasonal distribution of precipitation, but the notion droughts are getting more severe on average is certainly a false one.

    Even this increase is not uniform. Most of it happened in a single step of some +66 mm (15%) in 1973, and this level is more or less maintained since then. Interannual variation is huge, but it was always this way in Australia.

    It strongly suggests an abrupt climate shift in the first half of the 1970s, which is consistent with what we know about other parts of the globe. Perhaps ocean currents got rearranged a bit around that time, but unfortunately we didn't have our current advanced measurement systems in place to collect data during the event.

    It's extremely unlikely the phenomenon has anything to do with CO2, as levels were just 328 ppmv back then and they've increased by 19% in the last 38 years, apparently with no additional influence on interannual Australian precipitation patterns.

    Nevertheless I'm weeping for the dead and homeless, even if they're not victims of some man made climate disruption, just cruel weather.
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  3. Hi all,

    I think that we have to be clear in what the disussion is about. When we are talking about rain (and snow) there are two important things which are not necessary connected. If we look to the annual rain worldwide Precipitation worldwide, third graph (dutch) there is not really a clear tendency (the owner of this site is the 'national' wheather man in Belgium). Next to this it is also more difficult to measure precipitation worldwide then temperatures.
    A second point is of course the distribution of the precipitation. 10 times 10 liter is of course the same as one time 100 liters of rain but the effect is completely different.
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  4. KL:
    I saw somewhere else that the 1841, 1893 and 1974 floods were caused by cyclones. Is that true? In that case your argument that it is natural variation is completely off hte mark. Comparing cyclone floods to normal rainfall is apples and oranges.
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  5. BP #52

    You've done it again with your graph. Let me spell it out for you: it's worthless posting a line of best fit without also posting an assessment of whether the fit predicts better than chance (F statistic). It's also worthwhile posting the adjusted R-squared statistic to show how much variance is explained. Given the lack of power of time series correlations, your lack of diagnostic statistical analysis, your conclusion that "Australia, as a whole is definitely getting wetter on a century scale" is not justified until you do the additional work recommended above, and presented it.
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  6. michael sweet #54

    It seems to be fairly that the floods are the result of a strong La Niña phenomenon caused by ... wait for it ... unutually high sea surface temperatures.
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  7. Michael Sweet, the 1893 floods and the 1974 floods where both caused by cyclones following on from weeks of rain. It is uncertain whether 1941 was also caused by a cyclone, and there is no record (that I know of) that it was. This may be because cyclones can cause rain hundreds of kilometers from their center (as was the case in 1893, where the cyclone crossed the coast at Yepoon) and Queensland was effectively unsettled at the time so no record was made of the cyclone. It may also be because a cyclone was not involved.
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  8. kdkd @56, while most La Nina's will bring floods to Queensland somewhere, it is not common for them to bring major flooding to Brisbane without some additional factor (in the two best documented prior cases, a cyclone).

    Further, there is no data that suggests that warm SST cause La Nina events. If anything, globally warmer SST's tend to make El Nino events more likely. La Nina events certainly do cause higher sea surface temperatures around Australia, which leads to higher rainfall on the east coast generally, and more frequent cyclones in the tropical north and east coasts.

    On top of that, Global Warming (whatever the cause) has combined with the current very strong La Nina to create record high SSTs around Australia which is almost certainly a major factor in the very wet year that has been experienced by Australia, and also in the various flooding events around Australia at the moment. The fact that a La Nina is involved is why Queensland is coping it more than most. (And will continue to cop it, we can expect at least one or two major cyclones to make landfall in Queensland in the coming months, although the Northern Territory and northern West Australia will probably also cop a couple.

    And of cause, although a warming world will heighten the effect of La Nina events on precipitation in Australia whatever its cause, the cause is known to be Anthropogenic emmissions of green house gasses by fairly overwhelming evidence.
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  9. Eric, I would find this most recent graph
    interesting:



    It clearly shows the average SST around Australia over the last decade to be 0.6 degrees C over the 1950's average, and 2010 to be 0.8 degrees C over the 1950's average. The significance is that the final datum in your second source is circa 1950. Therefore Australia's current SST's are approximately 1.8 degrees greater than the minimum at the LIA.

    Given that the data from that site are for individual locations, while the Australian data is an average of all Australian waters, we would expect the Australian data to show significantly less variability (as would the data from the other site if averaged). Therefore it is reasonable to conclude that the Australian SSTs are near or at a maximum for the last 2000 years, not just the last 100 years.

    Of course, as you well know, it is voodoo science to simply point to a similar range of variability and assume that therefore no explanation is required. Changes require causes, and no non-anthropogenic causes can plausibly explain the late twentieth century warming. In contrast, it is difficult to device a plausible theory of the greenhouse effect in which anthropogenic emissions do not cause warming of similar magnitude that that which we have seen.
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  10. Tom @59,

    You beat me to it! Thanks.
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  11. Berenyi Peter @52, if you look at the trend map for precipitation over the same period, you will see that simply taking an Australian average hides a lot of devil in the detail



    In particular, the increase in average rainfall in the north of Western Australia and the Northern Territory clearly dominates the average, but that does not free Queensland and Victoria from their recent trend towards droughts in most years, nor Perth from its ongoing drought even in this wetest ever of Australian years.
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  12. Tom Curtis (and Albatross), the data from the chart in #59 seems to show as much variability as the chart in the paper I linked in #51 which is a measurement at a single location (albeit well north of Australia), so I'm not sure the averaging helps. The single location chart ends around 1950 at an anomaly of zero. The chart in #59 is at about 0.25 in 1950 (the gray bars) about 0.6 below the 1990's average as you said. That means the current anomaly would be 0.6 on the chart linked in #51 about 1/2 of the peak 1000 years ago. So the current measured SST anomalies are well within the range indicated by the proxies.
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  13. Eric @62,

    First, and FWIW, I for one actually appreciate (most of) your skeptical comments here.

    I need to look at the data more closely. The waters surrounding Oz have warmed significantly (> +0.7 C) since around 1900, with more than half of that occurring since the 60s.

    I'll get back to you once I've had a chance to look more carefully at the proxy data.

    With that all said, your argument about natural variability is a wee bit of a straw man...but more on that later too. My wife is going to give me heck-- Mma Ramotswe awaits.
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  14. John,
    I'm coming in on this late, but want to share my relief that you and yours are OK, while sympathizing with all who weren't so lucky.
    I've spent hours reviewing various skeptic sites today, especially Morano's fraud - it makes me want to scream.

    How do they manage to keep up their glib fraud?
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  15. Tom #58.

    I agree completely. You've taken my provision of enough scientific rope, and coiled it nicely on the deck, pending it's need for use some other time. The risk is of course that someone else will pick up your neat pile, tie it into a noose and slip.
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  16. Eric @62, to illustrate the point about averaging, here are the averages of the three data series from your second link for the first twenty terms:
    -0.37, -0.2, -.43, -1.3, -0.9, -0.6, 0.23, -0.23, 0.02, 0.07, 0.02, 0.6, 0.3, 0.51, 0.27, 0.6, 0.2, 0.07, 0.63, -0.1. The average used the same time step as the data for the Sargasso sea, averaging with the nearest value in time for the other series, or if no close value was available, with the intercept of the plot of the other data series. (Values judged by eyeball and calculated in my head.) The averaged values vary between -0.9 and 0.63, a range of 1.53. Over the same twenty time intervals, the values for the Sargasso Sea vary between -1 to 1.5, a range of 2.5. The averaged values, in other words exhibit only 60% of the variability of the individual data series. This reduction in variability is a well known property of multiple series, which is why temperature variability over multiple locations is not meaningfully compared as to variability with single sites as you have done.

    Of course, the more data points used in an average, the less the variability that survives. In this context, it is therefore relevant to list the data sources
    behind the BOM's SST product:

    "Data Acknowledgments
    The Bureau of Meteorology gratefully acknowledge the following institutions and data products that have been used to develop the system:

    BLUElink project partners - CSIRO and RAN

    Ocean General Circulation Model:
    Geophysical Fluid Dynamics Laboratory, Modular Ocean Model version4p0d

    Bathymetry:
    USNavy, US Navy 2 minute global bathymetry
    NOAA, General Bathymetric Chart of the Oceans, 1 minute global bathymetry
    Geoscience Australia, 1km regional bathymetry

    Satellite remote sensing:
    NASA and CNES: Jason-1, IGDR
    ESA, Envisat, IGDR
    NOAA, AMSR-E

    Real-time in situ observations:
    These are data made freely available from a large number of sources, through mechanisms such as the Global Telecommunications System of the World Meteorological Organization. For BLUElink they include specifically observations made by:
    Autonomous profiling floats (Argo)
    Expendable bathythermograph (XBT)
    Conductivity Temperature Depth (CTD)
    TAO/TRITON array"

    Clearly we should expect far less variability in the BOM's SST average than in data from a single location (or just three locations), and finding that reduced variability proves nothing.

    Tackled differently, there is clearly more variability in the individual years (range of 1.2 degrees) than in the decadal trend (range of 0.7 degrees) in the chart above, again indicating the effects of taking an average. If we look at more detailed data, say by lookiing at the the decadal trend for individual regions, we see a variability range of up to 2 degrees in some regions, such as the Gulf of Carpentaria. (We also see that the increase in SST in Qld waters has been significantly greater than that in Australian waters generaly.)

    I know you want to doggedly repeat a meme you have found comforting, but that is no substituted for analysis. Analysis shows the data you provide to approximately follow a pattern of warming to the peak at the MWP, then cool to a minimum at the LIA, and then warm again. If extended it would no doubt show the current peak at around about, or higher than that of the MWP. Those broad fluctuations of temperature, and hence energy content of the ocean/atmosphere system need an explanation, and as noted above, no non-anthropogenic explanation of the recent warming can be found that is consistent with the data - and not for the lack of trying. A significant proportion of modern climate scientists initially backed a different horse; but were dragged reluctantly to the IPCC position by shere force of data. No amount of prattling on about variability can obviate this fact.
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  17. This is my first time to your site, and I am a little overwhelmed with all the information.

    Most important things first - it's good that you and your family are safe. There are so many tragic stories about loss of life. My home on the Hawkesbury River (NSW) inundated in the '78 flood - all safe but still the memory leaves me a little too empathic with flood victims.

    I do have a question about climate change and the Queensland floods. With so much water over such a large area, can this have any immediate or lasting effect on climate?
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  18. Tom Curtis, an apples to apples comparison would be a wide area of proxies to a wide area of measurements (the BOM area is a bit small). Bob Tisdale's site had this chart http://i55.tinypic.com/2udz7yh.jpg showing about a 0.5 C rise which seems to agree with the BOM data. The AGW explanation is not in question here, just whether the variation is unprecedented.

    Here's a link to a (perhaps) better paleo proxy temperature study. Still only a few sampling locations, but they are spread out and their broader trends are comparable. Excel is also provided, here's the study http://www.nature.com/nature/journal/v431/n7004/full/nature02903.html Since there is virtually no modern data in this study, it cannot be used to compare modern changes, only past changes. It shows about 0.4C of rise and fall (figure 3b) from 2k ybp to a peak at 1k to preindustrial where the chart ends. There's not as much support for my "meme" here, but I need to find studies with more collection points, better resolution and modern data to be more certain.
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  19. Ken, hope things are starting to get a bit cleaner for you now.

    Just a management question. Will businesses get priority for electrical certification to reconnect? I'd hope so, but it'd be nice to be sure.
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  20. Tom Curtis #50

    You are correct in the difference between flood levels at the Port Office and the City Gauge. The Port Office level should be reduced about 1.4m to equate to the City Gauge. 1974 would have been about 0.5m higher that 2011 and 1893 over 3m higher than 2011 at the City Gauge.

    Every event has different characteristics, and the effect of the 'shock absorber' dams is generally one of mitigation.

    However, the strongest La Nina (probably on record) in Australia has produced a very wet year for most of the north and east except for the south west corner of WA.

    This is a similar pattern to 1974.

    Floods in Dalby and the shocking Lockyer Valley 'tsunami' also must take into account intensive agriculture of these areas which has a large effect on runoff behaviour.

    Rainfall in the Brisbane catchment heavily since September has been absorbed by Somerset and Wivenhoe; so the shock absorber was up near its stops.

    Half the water flow of the 2011 flood in Brisbane was from Wivenhoe, and the other half from below. A difficult decision had to be made to release water or exceed the dam's extreme capacity.

    Had the droughted dam (at 17% capacity about 18 months ago) received this recent deluge, we might have had a small flood if at all as Wivenhoe probably would not have released water over the critical couple of days.

    The point remains from the 1974 BOM report: "Meteorological studies suggest that rainfalls well in excess of those recorded in the floods of 1893 and 1974 are possible".

    This is a pre-AGW report which suggests that the limits of natural rainfall events could be well in excess of the 1974 and 1893 floods. 2011 might well be on a par with 1974, and AGW (a very strong La Nina) could have a part, but this is not strong evidence for AGW when the limits of natural variation are still largely unknown.
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  21. Eric, kdkd and Tom,

    Thanks for your posts. I have had a quick look at the data and run into some of the same problems that you have identified.

    Let us regroup. The record high SSTs were brought up in the context of the floods because research has shown that higher SSTs lead to higher PWV contents (e.g., Trenberth et al. 2005). That was the whole point of bringing up the SSTs. Whether the warming occurred 2000 years ago or presently (most likely b/c of AGW/ACC) is not in question here, b/c those historically warmer SSTs would have likely contributed to the acceleration of the hydrological cycle.

    Eric then seemed to decide to argue the strawman that "The AGW explanation is not in question here, just whether the variation is unprecedented.". Framing the argument that way entirely misses the point. Not to mention the vagueness of the period in question. Unprecedented in the last 2000 years? During the Holocene? Since the peak of the last interglacial? The PETM?

    The same argument (and a similar one trying to attribute the recent warming to natural variability) has been used by "skeptics" and those in denial about AGW/ACC to disregard the significance of the warming observed in the global SAT records.

    Anyhow, I feel a little awkward arguing about this on this particular thread given that the flooding has taken lives, destroyed and livelihoods.
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  22. Ken,

    Re: Wivenhoe

    At the end of September, Wivenhoe recieved sufficient inflow to boost to to 126.2% of capacity, which was then released back to 100%. Then in the week before Christmas it was boosted to 111.7% of capacity, which was then restored to storage capacity. In the week after christmas it was boosted to 120.5% of capacity which was then released. It then retained excess water continuosly from January 5th until reaching a peak at 188.5% of capacity on Wednesday the 12th. In other words, it was not "near its stops" but on its normal setting prior to the rain that brought the flood. Even had it been at the end of drought storage of 15%, it would still have been restored 73.4% by the post September 2010 rainfall. At a more normal dry period storage capacity of 70 to 80% (as through the 90's) would have brought it to 100% and made no difference.

    At its peak discharge, Wivenhoe was releasing 56% of normal storage capacity per day. Another 4% of storage capacity entered the Brisbane River from Lockyer Creek and other creeks between Wivenhoe and the city, with another 15% of capacity flowing in from the Bremer. So, had we gone straight from drought to flood, the total discharge down the Brisbane at the city would have been reduced to 48.4% of capacity, a reduction of 35.5%. That would, of course, have prevented major flooding, but the river would still have broken its banks at Graceville, Chelmer, and the West End. That should give a clear indication as to just how exceptional the current rainfall event has been. Brisbane never went straight from drought to flood even when it didn't have dams. That it could have done so with both Wivenhoe and Somerset as flood mitigation is extraordinary. (Data from Courier Mail and SEQ Water web site. To express figures as percentage of a Sydney Harbour, multiply by two.)

    With respect to the Lockyer Valley, intensive agriculture did not extend up the sides of the range, which remains forested. As the two most heavilly effected towns (Murphy Creek and Grantham) are close under the range on different creeks, the intensive agriculture had little effect on the outcome. Granted that after passing these two towns, a natural forest would have resulted in a slower runoff, but the damage past these two towns was not caused by the speed of the water.

    Returning once more to variability, I note that you again concentrate your discussion entirely on Brisbane, and leave out the truly extraordinary features of the 2011 floods. With regard to Brisbane, I note the following facts:
    "The" flood of 1893 (in fact the first of three) was brought about when Brisbane fell under the rain shadow of a third cyclone in succession.
    Another cyclone within a week caused minor flooding.
    A fifth and final cyclone caused major flooding that came within 0.27 meters of the first flood in depth.
    That means that flood was only 0.45 meters less than the heighest recorded flood since stettlement (ie, in nearly 190 years).
    The report into the 1974 flood notes that more rain fell in the Brisbane River catchement in the lead up to the 1974 flood than fell in the catchment leading up to the third flood in 1893 (they refer to the second flood on the table).
    Preliminary reports suggest the rainfall leading to the 2011 flood was twice that leading to the 1974 flood, suggesting that without flood mitigation the 2011 flood would have set a new record since settlement.
    Floods up to 2.5 meters higher than this again have been detected from geological evidence, which is consistent with aboriginal oral history.

    My point is obviously not that the 2011 flood is outside the range of natural variability (which it oviously isn't). It is that it is plainly pushing towards the upper limit of natural variability. On the assumption of no Global Warming we should find the 2011 Brisbane floods slightly surprising, both because they are only an (approx) one in 50 year event, and because they have occured without a cyclone. On the assumption of AGW we should find it less surprising, both because we expect such floods to occur more frequently, and because we expect them to occur with more normal (ie, non-cyclonic) rain conditions. Of course, AGW is not an assumption but a well evidenced theory with no coherent challengers.
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  23. Ken,

    "2011 might well be on a par with 1974, and AGW (a very strong La Nina) could have a part, but this is not strong evidence for AGW when the limits of natural variation are still largely unknown."

    Good, so you concded that AGW might have had a hand in this. That was the entire point. I'm not aware of people here citing this events as evidence that AGW is real. We know AGW is a reality, this event is likely evidence that the hydrological cycle is accelerating, especially when viewed together (as one should do) with the flooding in China, Pakistan, Brazil, N. America.
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  24. Albatross,

    This is a perfect place and time to argue the point. In the coming months, various governments in Australia are going to decide how to respond to these floods.

    If they think there is no AGW, they will conclude that Wivenhoe and Somerset functioned well, that perhaps a slightly improved algorithm for timing and quantity of water releases from Wivenhoe is called for, but that all in all it was a freak event that we probably won't see again for another 50 odd years. It might provide some impetus to look again at some of the canceled dam proposals such as Wolfdene and Traveston Crossing that would not have helped with flood mitigation anyway. Any serious responce will be considered without merit given the infrequent nature of the risk.

    In contrast, if they think AGW is a threat, they will think that events like this, and worse will become relatively frequent in the future. They will give very serious consideration to improved infrastructure for flood mitigation, and plan for rainfall episodes significantly worse than this.

    The view will make the difference between whether they consider this a typical scenario for the future (AGW) or a relatively rare near worst case scenario. If they take the later view, they will be wrong and it will cost lives.

    And if you think the opponents of AGW will hold of on this debate out of any sense of decency, you just need to check out the lies on Andrew Bolt's blog to be disillusioned on that point.
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  25. Tom Curtis #74

    After a morning of cleaning up debris - I really should not be doing this either Albatros.

    Tom - good points. I defer to your detailed knowledge of the capacity of Wivenhoe in the lead up to this event.

    There is some discussion in today's papers about whether Wivenhoe should have been run down to a lower level given warnings in October of the the very well developed La Nina and the high probability of a lot more rain through the summer with higher than normal cyclone activity.

    Of course coming out of a major drought - it would have been a tough decision to run Wivenhoe below its 100% level given that it was down to 15% only 18 months before.

    While the general points about the limits of natural variability (2.5m higher than 2011) you concede - the huge volumes released from Wivenhoe at peak (56% of capacity by your numbers) do point to better micro management of the future levels.

    For example - timing of the releases to arrive in Brisbane city at low tide was a major factor in the peak levels reached and the number of houses and businesses inundated.

    With a high to low tide cycle of roughly 6 hours - being able to hold back releases for 6 hours at a critical point could make a large difference to the peak downstream. We were lucky that a 2.6m tide was not happening on the 12th and 13th of January. This is a utilitarian argument of course - those just below Wivenhoe might suffer more for the greater good of the major population centre in Brisbane.

    Maybe this points to running Wivenhoe with an extra 6 hours of peak 2011 discharge capacity in reserve (14-15%) so 'full' is no longer 100% but 85%. Or indeed if feasible - to raise the dam wall and increase capacity.

    Your final point is a bit of a stretch:

    "On the assumption of AGW we should find it less surprising, both because we expect such floods to occur more frequently, and because we expect them to occur with more normal (ie, non-cyclonic) rain conditions. Of course, AGW is not an assumption but a well evidenced theory with no coherent challengers."

    Firstly, the difference between a cyclone which weakens into one, and low which develops into a strong rain depression can be very little.

    Wanda in 1974 came in at Maroochydore headed SW and sat in the Brisbane catchment as a slow moving rain depression - not unlike this week's event.

    No serious 'skeptic' argues that the planet has not warmed in the last 100 years. There are 'coherent challengers' to the proposition that the temperature rise observed (0.7-0.8degC) is mainly man made, and what its future trajectory might be.
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    Moderator Response: [Daniel Bailey] See my response to you at comment 78 below and respond to its criticisms on the appropriate threads. Thanks!
  26. Albatross #73

    Not so fast Albatros. I was a little sloppy in conceding AGW might have had a hand in this extreme event.

    I should have said GW might have had a hand, although even Tom Curtis has added above that Aboriginal history confirms that event 2011 + 2.5m could be more like the limit of natural flood variation in the Brisbane area.

    You know the rule in this wide brown land; the flood relief claim is going in just after the last drought relief cheque has been received.
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  27. Ken @75,

    I have seen several suggestions that SEQ water should have maintained dam levels significantly below 100% of normal capacity going into a wet season. This seems dubious to me on at least two grounds. First 100% capacity is the designed capacity to ensure Brisbane does not run short of water, a designed capacity already proven insufficient by the recent drought (and given AGW, likely to be proven insufficient at least once every 20 years going forward). The second point is that it is not even obvious that SEQ could run down the capacity. SFAIK, normal capacity is level with the bottom of of the spillway. In other words, running the dam below normal capacity can only be achieved by pumping, and pumping cannot keep up with high levels of inflow such as experienced over the last few months.

    As to the timing of water releases, SEQ is very mindfull of the risks to those downstream. It has been suggested that they should have retained more water over the critical period thus lowering the level of the flood. However, even running the dam up to its maximum capacity would have only halved (approx) the water coming over the spillway, which would still have meant moderate flooding in Brisbane, but left the dam absolutely no flood mitigation capacity for the expected additional 12 hours rain. (That rain did not eventuate, but hindsight is 20:20.) It would also left no capability to react to a second Toowoomba/Lockyer style downpour. While I'm certain the algorithm used to determine amount and timing of releases will be improved from examination of this experience, I do not think the improved algorithm will be very different.

    I doubt it is practical to build up the dam wall. Currently the Brisbane Valley Highway runs over the dam wall, and there is no noticable gradient on either side of the wall. The only way to increase the size of Wivenhoe would be to extend the length of the dam wall by several kilometers (probably by 10 to 20 kilometers, and possibly more, and to flood out several Brisbane Valley communities.

    Finally, I think you are underplaying the significance of Cyclones. Having spent the majority of my 50 years in Queensland (including the last 37), I can tell you that rains such as we just experienced have accompanied every Cyclone I have been near, even when "being near" has meant living in Mount Isa while cyclones struck Normanton or Townesville. I can also say I have never experienced rainfall as continuos and heavy as that when not in the rain shadow of a cyclone.
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  28. Re: KL @ 75 above

    (this wasn't very readable in the moderation box)

    1. You say:
    "No serious 'skeptic' argues that the planet has not warmed in the last 100 years."
    At Skeptical Science this battle is brought to us almost daily.

    2. Then you say:
    "There are 'coherent challengers' to the proposition that the temperature rise observed (0.7-0.8degC) is mainly man made"
    Then you should have no difficulty supporting this claim with links to peer-reviewed sources, should you? Just put them on the appropriate threads.

    3. Then you say:
    "and what its future trajectory might be."
    Unsupported hand waving again. Repeat response to #2 above.

    The Yooper
    0 0
  29. #71, Albatross, yes I was vague since I switched from 2000 years in #51 (because it was based on only one location) to the Holocene in #68. My less vague view that while the current SST enhancement is partly AGW, the range is normal for the Holocene. Which isn't saying much.
    0 0
  30. Tom Curtis #77

    I was looking at Cape Moreton from Caloundra on the Friday before the deluge - and wind gusts of 40-45 knots were being experienced. There was a fairly intense low winding up but it never reached cyclonic wind speeds.

    It is common for cyclones to have less rainfall when the wind speeds are highest, with the major rainfall occurring after weakening into a more or less intense rain depression.

    Interestingly enough - the latest Standards Australia Wind Code notes that wind speeds for the Region C up the Qld Coast should be arbitrarily uplifted because of the lack of measurements from Qld cyclones in the last 30 years. The action seems to have shifted to the north west of WA, where Cat 3, 4 and 5 cyclones have been much more prevalent.

    Qld is overdue for a 1960's-70's (eg. 1967 and 1974) season where 4-5 cyclones cross and the odd one runs down the coast - even as far as Maroochydore.
    0 0
  31. Ken,

    What makes cyclones a particularly potent source of rainfall is the massive convection cell driven by latent heat draws moist air in from a very large surrounding area. When the cyclone dissipates, that moist air (which has not already released its moisture in rainfall) procedes to do so.

    In contrast, a normal rain depression will not have concentrated the moisture in the first place, so while they are potent sources of rain, they do not have the shere abundance of available moisture that an ex-cyclone will carry with it. They do draw moisture into the center from the surrounding area, but having never been as intense, they never draw in as much.

    I don't think there is any such thing as "over due" in climate science, but certainly the conditions are ripe for a bumper cyclone season this year.
    0 0
  32. Thanks Tom,
    I read your posts with much interest, since I was handed Christopher Booker's "What was the role of warmists in the Queensland flood disaster?" ~ The Telegraph 1/19/11 {I visited and liked your website too}

    You've managed to answer most of my questions regarding Booker's claims. However, I'm curious if you have any comments about the land zoning claim he makes?

    Are you familiar with the reporter?
    ~ ~ ~

    "For years, Australia’s warmists have been advising the authorities that the danger posed to the country by global warming is not floods but droughts: not too much rain but too little. One result, in Brisbane, was a relaxation of planning rules, to allow building on areas vulnerable to flooding in the past. As long ago as 1999, this was seen as potentially disastrous by an expert Brisbane River Flood Study (which was ignored and for years kept secret). Instead of investing in its flood defenses"

    peterm
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  33. It is of course difficult to say just how much worse this particular flood was than it would have been without global warming. But it does raise an important point. When calculating the cost of climate change, is this sort of event factored in?
    0 0
  34. John, don't know about calculating costs in government policy, but cost will certainly figure in your next premium on your insurance policy.
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