Caveat empty: the question of Cubbie
20 August 2009
Now that the massive cotton farm Cubbie Station in southern Queensland is for sale, we need to consider whether it is a good idea for the federal government to spend public money to buy it and its 500,000 megalitre water licence for the benefit of downstream ecosystems and the Murray-Darling Basin.
It might not be the good idea that it appears, as the $450 million price does not guarantee 500,000 megalitres of water will be available. In fact, there is unlikely to be any significant flows in the river system concerned - the lower Balonne - in the near future. And even if there is, spending a large proportion of the government's water licence buy-back fund on Cubbie is unlikely to reduce stresses in the lower Murray-Darling.
Buying the Cubbie water entitlement would be of direct environmental benefit to the Lower Balonne floodplain. It also contributes an average of 16 per cent of the flows in the upper Darling, but with very high variability. More importantly, we have calculated that the probability of significant flows occurring at Cubbie Station has been decreasing steadily over the last 20 years.
Coupled with long range forecasts, based on the return of El Niño, this suggests that the region will remain dry well into next year, and the number of significant flows may further decrease into the future.
According to our forecasts, the chance that monthly flows in the river above Cubbie Station will exceed 35 000 megalitres per month has dropped from approximately 60 per cent before 1980 to less than 20 per cent today.
The 1970s and 1980s were substantially wetter than the rest of the century, but the drastic decrease in the chance of high flows is most likely due to climate change. This causes both increased evaporation and lower rainfall and runoff. On top of that, we believe increased extraction of both surface water and groundwater in the river system above St George has reduced flows.
In other words, our analysis suggests the government would be spending a large proportion of its buy back funds on water that is not, and may never be, fully available.
The question the Government should be asking is which parts of the Murray Darling Basin can be saved with the approximate $3.5 billion allocated for water buy-backs. The answer is unfortunately not all of it. Given this difficulty, any decisions to buy allocations need to be based on solid forecasts of future flows based on good science and taking into account changes in climate and landuse.
A further important consideration is the value of Cubbie as an agricultural producer. Given the projected shortages in global food production, it is Australia's interest to maintain the station as a productive agricultural enterprise which supports local communities. Based on the flow projections the best strategy for ensuring a sustainable future for Cubbie Station would be a shift to crops needing less water and significantly reducing its irrigated area.
Floris van Ogtrop and Willem Vervoort in the Faculty of Agriculture, Food and Natural Resources at The University of Sydney.
Contact: Dr Willem Vervoort
Phone: 02 9351 8744