Climate change increasing risks to Australia’s water security

Across the water industry in Australia, water planners are grappling with the problem of managing water resources under increasing climate uncertainty.

The impacts of climate change need to be more carefully considered in assessing likely future water availability and the responses of catchments to such availability.  Climate-change impacts are projected to become increasingly pronounced, especially within the next 20-50 years.

Climate change is increasing Australia’s already high climate variability, leading to more extreme climate events, increased temperatures and reduced rainfall. Water planners need to take into account the projected negative outcomes of climate change.

While it is not possible to remove all the uncertainties around future climate, we need to carefully consider if our existing decision support tools are capable of helping managers consider and plan for future climate variations in the water resource sector.

Review of current water models’ ability to incorporate climate variability and change

Water models help inform decision-makers concerned with making water allocation or water quality decisions.

Alluvium Consulting, in partnership with the University of Newcastle and CSIRO, was commissioned by the Queensland Water Modelling Network (QWMN) to undertake a critical review of climate change in Queensland water models.

The review assessed Queensland Government’s ability, as of May 2019, to incorporate existing climate variability and future climate change projections into the diverse range of water models used across Queensland, as shown in Figure 1. However, the criteria developed in this project is applicable to all states in Australia and to different types of water models, including those with agricultural and ecological applications.

Figure 1: Models used in Queensland for water modelling and their connections

 Our approach to the review was to investigate a variety of evidence, including reviewing the climate science (variability and climate change); interviewing those involved in modelling; workshopping the current and possible future state of play; and assessing four Queensland case-studies.

Models use 130 years of climate records, underestimating climate variability and change

Variability in Australian river flows are naturally very high, whether that be between years or decades. We found that most existing water models assessed hydroclimate risk by using the 130 years of historical instrumental climate records.

This data is likely to underestimate the cycles of climate variability and should incorporate the longer paleoclimate record. This record has identified eight megadroughts (that lasted from 5-39 years) between 1000 and 2009AD, which indicates a history of longer and more severe drought periods.  Existing water models are unlikely to represent this full range of climate variability.

Likewise, current water models do not properly consider or incorporate the impacts of climate change in assessing likely future water availability and the responses of catchments to such availability.

The impacts of a changing climate, and the adaptation strategies to deal with them, need to occur at more regional and national scales than those that Global Climate Models can provide. Greater detail, including more accurate representation of local extreme events, can be provided by using high resolution Regional Climate Models.

We found that the projections from climate models should be used together with hydrological modelling to assess the potential impacts of climate change on water availability, catchment hydrology, and river flow characteristics. Figure 2 summarises the modelling components needed to robustly predict future water outcomes

Figure 2: Modelling components and the sources of uncertainty in predicting future water outcomes

However, while many water models don’t explicitly consider climate variability or change, some have to the potential to be adjusted enough to sufficiently account for it. The Aussie Grass model is one leading example where they acutely understand the variability of future climate scenarios and account for it.

Need to focus on the needs of decision-makers

There are numerous complex model interactions and modelling tools available to assist end users in their roles as policymakers, planners, advisers, operators and regulators, as shown above in Figure 1.

The use of water models in supporting these functions is not new, but there is additional complexity when considering climate variability and change. Water modelling usually considers climate variability by using available, multi-decadal climatic records. However, decision-makers are now seeking additional information and analysis to provide evidence for their decisions and risk management.

Those making decisions about water now seek answers to questions such as:

  • As the historic record does not adequately account for potential climate-based risks in the future, what other information can we use with historic data?
  • In what ways is climate change likely to change our risk profile?
  • How uncertain are modelling results?

Model improvements need to focus on how best to answer the decision-maker’s modelling questions. This means there needs to be a flexible and adaptable modelling process that has clear objectives and well-communicated modelling outcomes to inform planning and policy.

This ‘pipeline’ process of modelling needs to address a range of questions when improving climate-change modelling, whether this be from the perspective of the modeller, or those using the results of models in decision-making. This is illustrated in Figure 3.

Figure 3: The modelling ‘pipeline’ needed to account for climate change

Decision-makers and water modellers need to jointly build in considerations of climate variability and change from the start when using modelling to answer policy questions.

Modellers need to ask decision-makers: Do you understand what you’re trying to model and is climate change important for that?

Once that question is understood, the modeller can then ask follow-up questions like: How good is the data you’re using? Are those data sets at the right scale to answer your question. Do you understand the socio-economic response to climate change? And over what trajectories?

By taking a step back and making sure the right decision-making framework is in place to fully understand and apply the outputs of a water model is just as important as accounting for the technicalities involved in building or calibrating a suitable model.

Ultimately, improving models to account for existing climate variability and future climate change needs to be based on improving the knowledge, capacity and communication skills of all those involved in using models to support decision-making.

Guidelines for assessing water models and their ability to be climate ready

To help water resource managers evaluate the models they use for decision support, we developed guidelines to help assess water models: Making our water models climate change ready: Are they up to the task?

The guidelines provide a ready reckoner to modellers and decision-makers to help them understand the ability of particular models to answer key questions associated with existing climate variability (using historical recorded climate data and paleoclimate records) and future climate change (accounting for trends in climate change and changes to existing climate variability into the future).

The guidelines are applicable to all Australian regions and water modelling questions.