The rivers of the Murray-Darling Basin are dying. While average inflows decline due to climate change, extractions for irrigation remain at environmentally damaging levels.
But the plan for management of the basin’s water resources drawn up by the Murray-Darling Basin Authority (MDBA), due to be adopted by federal parliament later this year, ignores fundamental problems.
Unscientific and politically-driven, the plan needs to be torn up, and the tasks of saving what can be saved of the rivers, their ecosystems and their human communities addressed afresh.
Large flows in the rivers during the wet La Nina years of 2010 and 2011 have allowed irrigators to receive their full water entitlements, and floodplain environments have received desperately needed inundations.
But in the southern part of the basin, which accounts for the great bulk of the inflows, forecasters predict a brutally dry winter. In these regions the unprecedented “Big Dry”, which lasted from 1997 to 2009, may be about to resume.
Rainfall in southern Australia is on a downward trend, in a process with well-established links to rising global temperatures. Now, a new study suggests that as warming proceeds, the effects will include more rapid and severe reductions in rainfall than previously believed. As if this weren’t enough, runoff to the Murray-Darling Basin rivers will also decline as a result of higher evaporation and lower soil moisture in the new, warmer climate.
For the many towns around the Murray-Darling Basin that have their economic base in irrigation, the future looks scary.
One result of warming will be tropical-style deluges that produce floods of staggering size. These will fill water storages, but also destroy crops and wreck housing and infrastructure. Even so, inflows will not be enough to sustain the river ecosystems, let alone permit diversions for irrigation on anything like the present scale.
Rainfall decline
Climate modelling from recent years projects that by 2060, median annual rainfall over the Murray-Darling Basin will have declined by 5-15%. Ominously for the rivers, a 1% drop in rainfall in the region typically results in a decrease in inflows of 3-4%.
But the new study indicates that for a given increase in global temperature, the “water cycle” of evaporation and rainfall speeds up far more than earlier thought. This conclusion rests on ocean evaporation data from salinity readings collected by thousands of automatic, free-floating buoys.
Lead author Paul Durack said the study by the CSIRO and the California-based Lawrence Livermore National Laboratory found that the world’s water cycle had accelerated over the past 50 years at twice the rate predicted by existing climate models.
For every degree of surface warming, evaporation and rainfall are now believed to rise by about 8%.
What this really means, co-author Susan Wijffels told Agence France Presse, “is that the atmosphere can actually shuttle more water from the areas that are drying out to the areas that have lots of rain faster ... the wet areas are going to get wetter and the dry areas are going to get drier”.
For the drying Murray-Darling Basin, this is not good news. The rate at which rainfall will drop may have been significantly underestimated.
As also noted, higher evaporation from land surfaces will further reduce stream flow as temperatures rise. In 2008, CSIRO researchers Wenju Cai and Tim Cowan concluded that in the southern Murray-Darling, “a rise of 1°C leads to an approximate 15% reduction in the climatological annual inflow”.
This effect will be irrespective of rainfall. Cai and Cowan suggested that a rise in global temperatures of 3°C above present levels, widely forecast for later this century, would cut average flows by about 45%.
How much will stream flows decline overall? For a rise in temperature of 3C over present levels, a reduction of 70% seems plausible, indeed likely. Moreover, that is an average figure; annual flows are predicted to become markedly more irregular, with enormous floods and longer, more severe droughts. The Murray of the future, this suggests, will be an intermittent river.
Findings ignored
The MDBA’s draft plan, presented last November and now being reworked following numerous submissions, completely ignores findings such as those of Cai and Cowan. Faced with pressures from agribusiness groups, pleas from environmental NGOs and conflicting demands from various state governments, the drafters seem to have regarded climate change as one complication too many.
In reality, consideration of the science would have made the MDBA’s political task quite impossible. That task can be seen as giving sanction to a policy deadlock in which large-scale economic interests are set against environmental campaigners. Behind the cover provided by such a deadlock, a pro-business federal government could throw up its hands in affected despair – and proceed to shaft the environment, workers and working farmers.
Taking the effects of climate change into account would have blocked such an outcome by making the environmentalists’ case unassailable. As the scale of the damage was revealed, pressures on governments to take serious action against climate change would have mounted.
Whatever the case, the MDBA’s plan is based on historical average flows, suggesting that these will apply in future too. Historically, yearly runoff to the rivers has averaged about 24,000 gigalitres (billion litres), more easily visualised as 24 cubic kilometres. Before irrigation began, roughly half this amount reached the sea.
Water extractions in recent decades have averaged about 13,000 gigalitres a year. Not surprisingly, when diversions exceed the previous outflow from the system, the Murray now fails to reach the sea about 40% of the time, sometimes for years at a stretch. With reasonable flows, the river each year flushes about 2 million tonnes of salt out to sea. Without these flows the salt remains, poisoning wetlands and harming agriculture.
To counter past over-allocations of irrigation water, the MDBA is charged with setting levels for a buy-back of extraction rights. Its draft plan provides for the permitted total of 13,700 gigalitres a year to be cut by 2827 gigalitres, to be phased in over seven years.
Large-scale irrigators and their lobbyists protest that this level of cuts would bring economic ruin to the river communities.
Environmentalists say the cuts should be bigger, since the MDBA’s figure would still leave too little water in the rivers to protect ecosystems. The Australian said in June last year that a CSIRO report found that to preserve the health of floodplains and of the lakes at the Murray’s mouth, diversions needed to be reduced by at least 3500-4000 gigalitres.
A cut of more than 4000 gigalitres would be needed to meet the MDBA’s target for flushing salt from the basin.
Early in January the Wentworth Group of Concerned Scientists, which studies the Murray-Darling river system, released a 25-page criticism of the MDBA’s draft plan. Spokesperson Tim Stubbs said the plan “sets long term diversion limits on the assumption that there is no risk to river health from climate change”. The plan provided no information on how its provisions might cope with long dry periods.
He said the MDBA had “produced a draft Plan that manipulates science in an attempt to engineer a pre-determined political outcome”.
On April 13 a joint statement by 60 Australian scientists sharply criticised the MDBA’s draft plan. The scientists condemned the plan as “flawed because it was based solely on historical data and failed to take into account future climatic changes,” the Australian said.
The new normal
The climate change referred to may already have arrived. During the “Big Dry” years from 2000 to 2007, average annual inflow to the rivers was only 37% of the long-term average, by far the lowest ever recorded over a seven-year period.
Irrigation rights toward the end of the Big Dry were meaningless, with storages near empty and many allocations set at zero.
Among climate scientists, the talk is increasingly of such “freak” events as the Big Dry becoming more like the “new normal”. Not only are extreme weather phenomena becoming commonplace, but the extremes are themselves getting more extreme.
And it’s going to get much worse. Today’s haywire climate reflects global warming of about 0.8C since the mid-19th century. Warming of 2C is now thought to be almost impossible to avoid.
Large parts of the river environment are clearly doomed. In coming centuries, sea level rises that have been locked in by emissions to date will drown the South Australian lakes and send seawater hundreds of kilometres up the Lower Murray.
Further upstream, with average streamflows drastically reduced, the struggle will be to save representative samples of key ecosystems.
For irrigators in the basin, the best hope lies in new technology allowing them to use much less water, and more saline water. Such equipment could soon be commercially available.
But the adjustments will still be wrenching for the river communities. In the towns of the Murray-Darling Basin, hard-working people who have never had much are being sacrificed to the greed of the fossil fuel interests that alone profit from global warming.
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