Climate change and the Murray Darling Basin

With record rainfall in large parts of Australia in recent months there has been a bit of a tendency to think that normal service has been returned. But record rainfall is by definition exceptional. This is how the last three months look on the BOM maps:

Australian rainfall deciles August-October 2010

I understand there is an unusual conjunction of a negative Indian Ocean dipole (IOD) and a La Niña. When we have a negative IOD:

The research shows that when the IOD is in its negative phase, with cool Indian Ocean water west of Australia and warm Timor Sea water to the north, winds are generated that pick up moisture from the ocean and then sweep down towards southern Australia to deliver higher rainfall.


The study also shows that the IOD has a much more significant effect on the rainfall patterns in south-east Australia than the El Niño-Southern Oscillation (ENSO) in the Pacific Ocean.

The La Niña increases the chances of higher than average rainfall in most of the rest of eastern Australia as well as a more active cyclone season. On average.

The exceptionality of the current season can easily be seen by comparing it to this decile mean of 12 La Niña events:

Rainfall in La Nina years

The following image shows what happens in negative IOD years:

Rainfall in negative IOD years

That page also carries examples of the rainfall effect of combined IOD and La Niña years, showing how truly exceptional the current season is.

If you overlay these maps with a map of the Murray Darling Basin you can see that both would have a considerable influence on flows:

Murray Darling Basin

It is particularly misguided to think that current rainfall in the Murray-Darling Basin represents ‘normal’.

The MDBA deals with the impact of climate change in Chapter 4.2 of the Technical background paper which carries this graph of modelled river levels at Wentworth assuming no diversions:

Modelled Murray Darling River flows at Wentworth

I would suggest that it’s not possible to establish what the ‘normal’ pattern is. Nor can we say that the pattern of flows has reduced decisively and won’t recover. But it would be heroic indeed to suggest that the pattern from now until 2030 will return roughly to the average of the entire historical record for 1985-2009, yet to cut to the chase the MDBA has used a reduction of surface flows of only 3% in their planning and has deemed that likely changes in groundwater and sea level rise near the mouth will be too negligible to be considered.

In my view, admittedly limited, their stance can be justified by the science if their focus is the next decade, but it seems to me that the science is not particularly helpful. In other words we really don’t know what the heck is going to happen during the climatically short period we are planning for.

To back up a bit, climate models suggest that there is going to be an expansion of tropical weather systems leading to mid-latitude drying, as shown in this image from IPCC AR4 WG1:

Anticipated precipitation patterns

I understand that climate modellers work in grids of about 300 km square, so the predictions are coarse-grained and uncertain over a short time period like 2010-2030. But recent information indicates that we’ve seen in both the northern and southern hemispheres the westerlies retreating towards the poles.

So we have these winds that wrap around and around the mid-latitudes, and basically those belts of winds have been moving like shrinking doughnuts towards the poles of both hemispheres. And in the Southern Hemisphere it’s been even more dramatic. In the north it’s been about four degrees of latitude, in the south it’s been six degrees of latitude.

That’s 670 km. I’d suggest that ‘normal’ has gone forever.

There are something like 23 river valleys in the MD Basin and according to Chiew et al there is a clear run-off gradient from less than 10 mm in the west to more than 200 mm per annum in the SE. This is illustrated as follows:

Annual runoff

It’s no surprise, then, to learn that the Upper Murray catchment alone with 1.4% of the area accounts for 17.3% of runoff.

And, indeed, the South East is where the biggest reduction has been:

Decrease in runoff 1997-2006

The image on the right shows the decrease averaged over the 18 MDB regions.

In looking at the 2009 Steffen Report on Australian climate I gave this summary:

Progress has been made in sorting out what is happening with the climate in Australia. The shorter story is that there is a clear climate change signal in the drying pattern in south-west Australia in recent decades and in the lower edge of the Murray-Darling Basin. There is some evidence of a climate change signal in the drying trend in Victoria and the lower half of South Australia. In Northern NSW and Queensland it is too early to say.

Steffen notes that increased heat alone will reduce run-off by 15%.

The most important factor in terms of MDP planning is that they intend to do it all over again by 2020. Hence the focus is effectively instant in terms of climate change.

The MDB Technical report notes the extreme variability of run-off in the past. In the wettest 15-year sequence (1050-1964) flows at Wentworth were 42% higher than the long-term average. In 1995-2009 flows were 32% lower. Climate models indicate a variability of +7% to -37% by 2030. A ‘median’ climate scenario of -10% is derived, which they scale back to -3% for the current planning period.

You can’t fault this on scientific terms but variability and uncertainty seem to be key concepts, especially since water allocations are low in dry years and high in wet years. Since, according to Chiew et al, run-off is only 27.3 mm of precipitation of 457 mm (long-term average) the whole business of irrigation seems extremely marginal. Some usage can be opportunistic, but people, trees, vines, farm animals and many of the environmentally sensitive areas require continuous access to water. Moreover the lower part of the basin, say from Mildura down, contributes very little run-off and hence relies on rain falling further up.

Clearly priorities are going to have to be set across all users, in each valley and across the basin as to what kind of river and what uses are sustainable. The proposed reallocation to the environment is astonishing when represented graphically and numerically (see Figure 4.11 and table 4.4, pp 111-112).

The Lower Lakes present a peculiar problem in terms of climate change.

The best that science can offer is that current levels of CO2 imply an eventual sea level rise of 25 metres, plus or minus five. Everyone concedes that to reach this level will require centuries and probably upwards of a millennium. But most scientists and planning authorities that take sea level rise seriously are reckoning on 1.0 to 1.2 metres by 2100, with risk on the upside. The long-term viability of the Lower Lakes as a freshwater system becomes a question. If you want to return the Lower Lakes tidal system to a ‘natural’ state a prime condition is that you have to cease all water diversions upstream.

But that’s assuming no sea level rise, past or future. Without a barrage, saltwater incursions would reach Murray Bridge at 1 metre rise. You can check levels up to 14 metres on this flood map. At 14 m you get significant incursions up as far as Loxton.

Skeptical science has recently done a post looking at The Eemiam interglacial 116,000 to 130,000 years ago when the temperatures reached 1.9C higher than pre-industrial. That equates with the 2C guard rail currently adopted for a ‘safe’ climate. Sea levels were 6.6 to 9.4 metres higher (midpoint 8 metres) than now. This is what you get:

Lower Murray with 8m sea level rise

So removing the barrages is not an exercise in restoration, rather a commitment to continuously increasing saltwater incursion. Yet if we are not going to adopt aggressive mitigation it may be better to relinquish the lower lakes and put the barrages above them so that Adelaide can continue to draw water.

One way or another as the century progresses we are going to have to make some stark choices about what kind of river we want. Already particular river communities are suggesting (for example the Lachlan) that their water goes practically nowhere downstream. The technical report stresses the interconnectedness of the whole basin, but with drying this will become less and less true. No community of interest across the whole basin can be assumed.

The earlier post is here.

Mike Young, a member of the Wentworth Group, has a site devoted to water with Jim McColl of the CSIRO.

The House Standing Committee on Rural Australia has a Inquiry into the impact of the Murray-Darling Basin Plan in Regional Australia

Here’s a perspective from rural Australia.

Here’s a somewhat jaundiced appraisal of the worth of the Wentworth Group.

33 thoughts on “Climate change and the Murray Darling Basin”

  1. Great stuff Brian.
    Thank you.

    May I offer one small carping trivial negative comment?
    Why did you include the ‘jaundiced appraisal’ from the flat earth society?

  2. I agree with this summation, regretably, but the end result is inevitable.

    This is the reason why

    The methane time bomb is in the process of detonating. How will it play out? Just like a nuclear explosion. First will come the flash..of news coverage, then there will be the draw in as temperatures appear to decline (pretty much what we are experiencing now) as cold air from rapidly melting ice flows away from the poles, then there will be the full blast as temperatures rocket upwards dramatically causing devastaing high pressure systems at the higher latitude edge of the Hadley belt and unprecedented cyclones and flooding rains in the tropical belt. Sea level rise will take a few decades to become totally devastating, but just as radiation is the ultimate killer in the nuclear scenario, the flooding of our coastal cities will cause the final devastaion of our economies. The only safe place will be high and dry and underground (natures ultimate survival strategy).

    Of course Howard will be dead by the time this all plays out but I am going to make sure that my kids stomp on his grave every year that they can. And depending upon what happens in the coming years, those Labour ratbags too.


    Something went wrong in my previous attempt to post this comment/link.

    That is a link to Gary Sauer-thompson discussing Brian Toohey’s article re the government which “has no intention that the $5.8 billion public investment to upgrade commercial irrigation infrastructure will not be recovered.”
    as in:
    “In line with Rudd’s approach, Gillard has no intention of recovering a cent of this public spending from the irrigators who benefit.”
    “It is a policy failure because it amounts to a gigantic public subsidy for the irrigation industry, which regards the water flowing into the nation’s rivers or underground aquifers as belonging to them. ”

    Thats pretty sloppy cut and pasting on my part, might be best to go to the originals.

  4. Help, I’m think I’m caught in moderation or spam trap or time warp …or somthin’.

    [It was spam, released now – Brian]

  5. Thanks for this article. I am a convert – but will our politicians absorb this information?

    I find the Elders Weather site easier to read to understand that the rainfall that Melbourne has received so far in 2010 is just above average, hardly drought breaking. You can check the climatelogy for other weather stations, but check whether the weather station was established 20 years ago or 150 years ago.

  6. hd @ 1:

    May I offer one small carping trivial negative comment?
    Why did you include the ‘jaundiced appraisal’ from the flat earth society?

    Because it definitely wasn’t the flat earth society and, as far as I can tell, it wasn’t fat earthers, but people whose comments are considered moderate in that audience.

    I saw an online survey in Qld Country Life last year, which from memory, came out as 47% sceptical or denying AGW, 42% accepting it and the rest don’t know or sitting on the fence. Or thereabouts. A negative review of Ian Plimer’s book by Matt Cawood had some support. The pro-AGW gets a pretty fair run in the rural press, actually, because much of the content comes from Fairfax. But on the internet blogs and in letters to the editor etc the anti-AGW side simply dominates and has to be accepted as being there by policy makers.

    I tossed up about it, but put it in because of the above.

  7. Brian this is interesting, but the proximate influence on water entering the river system is, surely, run off, not rainfall, and certainly not (as you recognise) basin-wide annual rainfall, given that three quarters of all run off in the MDB comes from the relatively small area of the Snowy Mountains.

    There are a lot of variables impacting on run off that have nothing to do with rainfall – land management, increasing numbers and capacity of farm dams, salt interception schemes etc. One of my bugbears is how little attention is paid in particular in this debate to interception of water by increasing vegetation in the MDB – more forestry (I have seen that on its own estimated as accounting for 750GL less run off, basin wide), but more particularly vast areas of increasing undergrowth and generally unmanaged revegetation as Native Vegetation Acts have begun to bite.

    Over-the-top green legislation may need reconsidering, for this as well as fire reasons?

    Also, forgive me if I say that, since the scariest IPCC4 scenario for sealevel rise by 2100 is 59 cm (not 1-1.2 metres), your illustration of what would happen with an 8 metre rise is to say the least somewhat irrelevant. You wouldn’t want to start sounding like Al Gore, would you?

    Good piece though, thanks.

  8. Thanks, Brian, that’s fascinating (and sobering).

    It seems to back up my gut feeling that this current unusually wet year is a once-in-a-century (or maybe never again) opportunity that shouldn’t be wasted on growing cotton, rice, or wine grapes.

  9. Thanks Brian for a very sobering analysis. I read it shortly after listening to the NSW Countryhour where a discussion between, I think, NSW Ag Minister Steve Whan and compere (it hardly matters as it is vogue thinking for all MDBA discussions) and the question of ‘balance’. ‘Getting the balance right’ between environmental flows and irrigation extractions is fast becoming an impossibility in light of your, Will Steffen, BOM, IPCC et al predictions.
    Balance suggests an equality of water either side of a fulcrum, a finite quantity of water determined at a particular time of the year, based on reasonable predictions. As you point out the short time frame of the MDBA assessment(2020) and the ‘elasticity’ of climate change, suggest that a proper balance is going to be very difficult if not impossible. It has become a political liability, a weasel word in Don Watson vogue. It may have some currency when talking about human institutions, eg IR laws for a centrist (Rudd/Gillard) government but IMO simply outlawed when it comes to the natural world.

  10. Thanks for an interesting analysis Brian. Some of the guys who are part of our research group here at the ANU have published an atlas of projected rainfall which might be of interest to you (link to pdf here).

    I’d also like to note that the decreased runoff in the SE MDB is likely due in large part to the 2003 bushfires, as new growth forest sucks a _huge_ amount of water. Studies of runoff from burnt old growth forest in Victoria after fires in the 70s (too lazy to find references to papers just yet, might post some later) show that it takes around 30 years post-burn for runoff to return to average, everything else being the same. Based on this stuff I suspect that runoff won’t return to normal for that part until ~2030, regardless of rainfall. This could be a big problem for water allocations, although I’m sure it’s being taken into account by the authority.

  11. The recent rains give the irrigators some breathing space but this doesn’t mean that some hard decisions need to be made about both farms and towns. For example:
    1. What should the water release policy be as storage levels drop?
    2. Where should water loss reduction levels be concentrated? (What, if any irrigation areas should be shut down permanently?)
    3. In the long term should Adelaide be allowed to take any water from the Murray Darling?
    4. Does it make sense for Qld water to flow all the way to SA?
    5. What water flow pattern does the environment really require?
    6. Should parts of the irrigation area operate on a fly in/fly out basis when there is a surplus of water?

    I could go on.

  12. As a life long weather watcher and purely from memory I related the “moving south” to the general position of the highs as they crossed the continent. The westerlies “heading for the poles” confirms for me the co-relation.
    As a former resident of Ashbourne and the Fleurieu Peninsula that map looks like water water everywhere and not a drop to drink.
    Thanks Brian for this excellent work.

  13. Wozza @ 8, there has been a lot written about sea level since IPCC AR4 in 2007. I’ve done probably 10-15 posts on it. IPCC left out ice sheets because of the inability of models to cope with them at that time and it’s becoming obvious that they are now in in play – certainly Greenland, the Arctic Peninsula and West Antarctica as a whole is looking wobbly.

  14. Yes, OK, Brian, I would be the last to defend the IPCC models. There’s a lot of things they can’t cope with, then and now, but that – and its implications – lead us into past disagreements better not revisited here. Sorry, I shouldn’t have succumbed to the temptation of a throwaway line.

    I still think vegetation policies are an important issue not sufficiently acknowledged, though, and that recovery from fire a la Jess@11 is not its only facet.

  15. DI (nr) @ 9, I don’t think we can be sure what new pattern will emerge.

    Billie @ 6, I wasn’t trying to convert anyone. Let me summarise what I think I learnt from doing the post.

    1. The current weather is exceptional rather than a return to normal, but we don’t know what is going to happen near-term except that there is likely to be a lot of variability.

    2. ‘Normal’ is an impossible concept, especially in relation to run-off.

    3. As the century progresses tough decisions are going to have to be made about what kind of river we want and how we allocate water amongst competing demands. Not all demands can be met and we are going to have to use triage to decide which sensitive environmental features can be sustained.

    4. There are particular problems with the Lower Lakes, saltwater and sea level rise.

    5. The MDBA has played a very straight bat on climate change, as their short time focus – effectively the next decade – allows them to assume almost the status quo.

    6. There is no commonality of interests running across the basin. So in a sense Windsor is right. The implications are going to have to be looked at valley by valley. But someone will have to take a broader view or Lower Murray users will be out of luck.

    Having opened up the discussion in relation to climate change, with some trepidation in relation to my lack of knowledge, I’m awfully glad I don’t have to make the decisions.

  16. Wozza, I can readily agree that vegetation policies are bound to be important, but frankly I don’t know anything significant about them.

  17. Brian 14

    The IPCC possibly left out ice sheets because they do not appreciably add to sea level rise, as they are already afloat and thus the bouyancy effect is automatically applied.

    As to the lakes, soon to become bays, this is an early adaptation that many Australians will be facing over the next 50 years. As with any business facing change (I’ve experienced this several times) it is far better to be in control of the process of inevitable change than to become a victim of it. ie plan the date when the lakes will be salty and control the transition while improving the lot for those upstream, rather than wait for the next drought to force it.

  18. Brian, Radio National and Tim Flannery and members of the Murray CRC taught me that climate change means that south eastern Australia is drying out. I think you give a very clear summary of the issues.
    In Crikey today Murray Murmerings> says “most people (75%) [who live in the basin] continue to want water reform, they continue to see it as urgent (62%) and surprisingly, more people believe that it is likely to happen (60%).”

  19. Hi Woz,

    The experience of C19 settlers within central NSW catchment was that their “permanent” creeks dried up once their collective land clearing took hold.

    You get more runoff from shaded & forested land than from thirsty cleared evaporation-prone land.

  20. Alphonse, my dad took up a virgin brigalow block in 1921. He said the creek used to run for 6 weeks after, mostly clear. When I was young a quarter of a century later it flooded and ran for about 3 days most times, mucky brown.

    I don’t know which yielded the greater volumes.

  21. This is where our farming techniques have been disasterous.
    Non tilled farming is a big improvement along with the several farming systems developed to retain water. Do you guys know the names of the pioneers who developed the terraced terrain techniques with specific vegetation to retain water?

  22. You get far more runoff from cleared land but infiltration on forested or heavily vegetated land can produce a more regular flow which is more useable.

    Forests contribute hugely to maintaining a rain cycle which again produces a more regular flow.

    The aim should be to maintain maximum biomass for maximum capture of the sun’s energy for maximum fertility.

  23. BilB @ 18, I was going on memory. I did a post on what the IPCC did back in 2008, but all those posts have not been loaded yet in our present home. Best go back to Stefan Rahmstorf at RealClimate in 2007 in direct response to AR4:

    The main conclusion of this analysis is that sea level uncertainty is not smaller now than it was at the time of the TAR, and that quoting the 18-59 cm range of sea level rise, as many media articles have done, is not telling the full story. 59 cm is unfortunately not the “worst case”. It does not include the full ice sheet uncertainty, which could add 20 cm or even more. It does not cover the full “likely” temperature range given in the AR4 (up to 6.4 ºC) – correcting for that could again roughly add 20 15 cm. It does not account for the fact that past sea level rise is underestimated by the models for reasons that are unclear. Considering these issues, a sea level rise exceeding one metre can in my view by no means ruled out.

    They did include the ice-sheets but in a half-arsed, misleading way.

    In this piece I understand Rahmstorf to have done the IPCC calculations properly, taking full account of the historical increase in the rate. Rahmstorf cut his teeth on relativity physics, hence is reasonably good at mathematics, one would think. He came up with 0.5 to 1.4 metres.

    Then there is this 2009 piece:

    The Copenhagen Synthesis Report recently concluded that “The updated estimates of the future global mean sea level rise are about double the IPCC projections from 2007?.

    The calculations always assume linearity in relation to temperature increase. Towards the end he asks whether the relationship is necessarily linear. Of course, it isn’t.

    Then last December Climate Progress reported on a study by Vermeer and Rahmstorf showing that sea level rise could be three times what the IPCC predicted, or 1.9 metres.

  24. Forests contribute hugely to maintaining a rain cycle which again produces a more regular flow.

    Salient @ 23, I understand that in the Amazon half the precipitation comes from transpiration.

  25. David Suzuki was talking about exponential growth the other day(It could have been a repeat tho) and basically things happen very fast if you don’t acknowledge the initial problem.

    The world is facing a crossroad of problems!

    There are market potentialities here so why do we continue to acknowledge that we are the supposed clever country???

    We are far from the clever country if we keep voting Liberal and using fossil fuels to the benefit of the few!

    Who wants to boycott oil? We can only partially do this but we can probably do this to a greater degree than we think!



    The biggest problem the world is facing is an attitude problem… and the terrorists have already made big inroads on correcting that! The solutions are natural!!

    Live or die, man!??!

  26. Thanks, DI, that’s the one. The original keyline farm was recently up for sale to be subdivided for housing. Typical.

    There was another pioneer as well.

Comments are closed.