Why science can’t determine environmental water requirements for a healthy Murray-Darling Basin

By Dr. Samantha Capon

Protecting and restoring rivers and wetlands is a major goal of Australia’s ongoing water reforms. To achieve this, environmental water planning currently assumes that the environmental water requirements (EWRs) needed to support particular ecological management objectives (e.g. waterbird breeding) can be scientifically defined. If this is the case, the environmental benefits of different water management scenarios are relatively easy to evaluate – either a water management scenario provides defined EWRs or it doesn’t.

Murrumbidgee River
The Murrumbidgee River at Yanga National Park (photo: S. Capon)

The concept of EWRs, however, suffers from the ‘how much is enough’ myth – the idea that science alone can determine what is ‘enough’ without explicit social, cultural and political contributions.

When it comes to watering our wetlands, what is ‘enough’ will always depend on subjective value judgements. “It is impossible to ask ‘how much is needed?’ without simultaneously asking ‘what is it needed for?’”.

This insinuates that EWRs could be scientifically determined if environmental objectives were simply defined more clearly and equitably. We argue in our recent paper, however, that this is also impossible because of the dynamic and diverse nature of the Murray-Darling Basin (MDB) and the many ways in which it’s wetlands are valued by people.

We identify several major misconceptions underpinning environmental water management planning in the MDB.

  1. Water-dependent ecosystems in the Basin are adapted to specific historical flow regimes: Actually, many water-dependent species in the Murray-Darling Basin (e.g. river red gums) are opportunistic, highly adaptive and occur across a range of climatic zones and hydrological conditions.
  2. Survival and/or reproduction of water-dependent species ceases beyond certain flow thresholds: There is very little evidence for ecological thresholds and, even if these did occur, past tipping points are likely to shift in the future under climate change.
  3. Ecosystems have an optimal state: It is impossible to know what ecological state might be optimal at present given uncertainty about the future.
  4. Ecological resilience is always desirable: Managing for resilient species and ecosystems in the present may limit their capacity to adapt to conditions in the future.
  5. Ecosystem health can be objectively measured by good science: assessments of ecosystem health are unavoidably dependent on social, cultural and political inputs in addition to science.

We propose an alternative approach whereby science contributes to environmental water decision-making by focusing on describing ecological responses to different water management scenarios and linking these responses to the ecosystem services and human values which they provide.

This work appeared in Water Economics & Policy



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