We need to plan for what we fear, not just what we expect

The Murray-Darling Basin Authority (MDBA) – the statutory agency responsible for planning the Basin's water resources – has just shared the starkest news yet about the Basin’s future: the Basin is almost certainly going to get hotter, drier and more volatile in the future, with reduced river flows.

The Authority’s latest major reports – the Sustainable Yields, the Outlook, and the Basin Plan Review Discussion Paper – paint the clearest picture yet of how climate change is reshaping the Murray-Darling Basin.

But the reports also highlight something crucial: while the direction of change is clear, the size and timing of impacts remain deeply uncertain.

Why does uncertainty matter?

The instinct in water planning is often to “pick a climate future” (a dry one, or a wet one) and plan around it. But the Basin could change in many directions and at different speeds.

Rather than trying to predict exactly which climate future will unfold and which of our climate models will be 'right', researchers increasingly argue that this is the wrong goal.

We also tend to focus on things we’re comfortable with or understand well. This contributes to another kind of uncertainty – that of ‘unknown unknowns’, which if we ignore, risks blindsiding us to different kinds of future threats.

The computer models we use to project future basin and river conditions have remained largely unchanged since the last major Basin-wide assessment in 2009.

These tools are useful for what they were designed to do, which is to simulate water sharing between New South Wales, Victoria and South Australia, but they can’t do everything.

For example, they can’t predict things like the massive fish kills in 2019 or how crop types, land use or Basin communities will change.

What alternatives do we have?

We need a better way to handle the known and unknown uncertainties to inform decisions. Instead of trying to predict the future, we should be asking: What conditions cause our system to break? And which uncertainties matter for our decision?

In our recent work undertaken through the One Basin Cooperative Research Centre (CRC), we used a 'stress testing' approach for the southern Murray-Darling Basin.

Rather than using complex, slow models that run just a few scenarios – we used faster, simpler models to simulate thousands of different possible futures.

We adjusted rainfall, temperature and seasonality to push the system to its limits.

We learned where the important factors, like water allocation rules, start to break down – which happens under dry but plausible future conditions.

Our data showed that Victorian shares held up well against small drops in rainfall. But they have a hidden cliff edge. Once runoff drops beyond a certain threshold (around 20-25 per cent), the system crashes.

Similarly, environmental flow targets and ecological outcomes across the Basin are at significant risk when rainfall drops by 15 per cent.

Understanding this can improve adaptation planning. We can use these lessons to design strategies to avoid breakdown points or lessen their impacts.

Another technique we can use is called ‘storylines’. Here, we build a picture of the future that includes not just how the climate might change, but also how people will respond – something missing from our current tools.

Adaptation improves our chances of a good outcome

Instead of ignoring something because our current models can’t simulate it, we use other lines of evidence.

Other lines of evidence can include integrated models, past observations, Indigenous knowledge and expert brainstorming to give us insight into how things might change, including those 'unknown unknowns'.

This all becomes more important when we consider the need to adapt to climate change.

We want adaptation options that help Basin communities and the environment across a range of future climates, not just one single ‘prediction.’

Our research can help find options like reconnecting rivers with their floodplains by showing how their benefits change across thousands of different futures.

Preparing for the unknown

Adapting to climate change risk is everybody’s problem.

The MDBA’s Discussion Paper for the Basin Plan Review highlights the need to continue investing in science to improve our understanding of environmental, economic, social and cultural interactions as well as support water management decisions.

We agree with this direction, but it's also essential to change the way we model water management scenarios, listen to diverse voices and broaden the tools we use to make decisions.

We have three main recommendations to improve the way we undertake climate change studies:

• Put modelling effort in the right places: Focus on sources of uncertainty and don’t be blind to novel threats. Don’t just model what we expect, model what we fear.
  
  
• Start with the decisions that need to be made and tailor methods to these: One model can’t do everything well. Different decisions depend on different parts of the system (for example, water flows have a significant impact on the environment and ecosystems), so the modelling must reflect the dynamics that matter for that decision.
  
  
• This is a job beyond science and research: Government, researchers and Basin communities need to collaborate to understand the risks and manage the impacts.

This all matters because we need to start adapting to climate change now. We know the Murray-Darling Basin is going to change, but we can’t know how.

If we lock in decisions based on a narrow understanding of the future or a legacy understanding of our rivers, we won’t be prepared for the shocks that come our way and we will suffer for it.

By stress-testing our rivers today and preparing for the unknown, we can design a river system better able to handle whatever tomorrow throws at us.

This article was originally published by Pursuit. You can find the original here.