What’s the science behind revised Murray-Darling environmental flows?

A decision on the Murray-Darling is on the way, but will it be evidence based? AAP

The past few days has shown that the issue of water reform in the Murray-Darling Basin is “back on the boil”. The current discussion is about what evidence is credible and how “evidence” is used to support policy goals.

This is an issue that goes well beyond water and reaches to the core of what researchers do, and how their work is used (or misused).

While everyone agrees that all policy should be based on the best available evidence there is often a big gap between what is espoused and what is practised.

In the water context there has been an on-going debate about the appropriate increase in environmental flows in the Murray-Darling Basin.

Many species rely on the river. AAP

Increased environmental flows would reduce the chance of environmental damage. This has included widespread die-off of river red gums and decline in the quality of habitat and abundance of many flora and fauna in the Basin over the past two to three decades.

As with all science, however, there is considerable uncertainty about the actual environmental outcomes of increased environmental flows.

Using the best available science, and drawing upon a wide body of peer-reviewed work, in October 2010 the Murray-Darling Basin Authority came up with a volume of water for the environment equal to 3,856 GL/year, on average. This would give a “high uncertainty” of conserving key environmental assets and ecosystem functions.

It also had a larger number of 6,983 GL/year that would give a “low uncertainty” of conserving key environmental assets and ecosystem functions.

Both of these numbers had confidence limits placed on them: ± 20% for the 3,856 GL/year volume and ±10% for the 6,983 GL/year volume. This meant environmental flows could increase by between 3,085 GL/year (high uncertainty of achieving environmental goals – 20%) and 7,681 GL/year (low uncertainty of achieving environmental goals + 10%). The Authority rounded this down to between 3,000 and 7,600 GL/year.

Everyone needs to know where the numbers come from. AAP

Based on these volumes, the Authority recommended that the increase in environmental flows should be between 3,000 and 4,000GL/year. That means between 27% and 37% reduction in water extractions by irrigators if this extra water were obtained entirely from reductions in water course extractions.

The upper limit was set at 4,000GL/year rather than 7,600 GL/year by the Authority because it believed that reducing irrigation diversions by more than 4,000 GL/year would result in unacceptably high socio-economic costs.

These proposed reductions generated a veritable storm of protest in some Basin communities. Some farmers burned the “evidence”: the Guide to the proposed Basin Plan released by the Authority.

The proposal also led to a parliamentary inquiry Chaired by Independent MP Tony Windsor. It will shortly report on the social and economic consequences of the changes proposed by the Authority.

On 25 May 2011 the current CEO of the Murray-Darling Basin Authority, Rob Freeman, told a Senate estimates hearing that the Authority had developed “new science”. He said it was more robust than what the Authority had available to it in October 2010.

Environmental flows have costs, and benefits. AAP

According to Freeman “…the assets and functions are now yielding numbers below 3,000GL/year”. Whether this is old or new, all science used to make public policy decisions should be scrutinised and, wherever possible, be subject to peer review. If not, the evidence is compromised.

Yet, so far, the Authority has refused to establish an independent scientific assessment panel to review its “new science”, despite an explicit request to do so by the Wentworth Group of Concerned Scientists, the Australian Conservation Foundation and others.

Where does this leave us? Intended or not, the leadership at the Authority risks compromising the evidence. This evidence is desperately needed to have an informed debate about the costs and benefits of increased environmental flows. Science isn’t the only loser; so are those who want policy decisions made on the best available evidence.