Climate modelling

The following frequently asked questions are about climate modelling.

What is the new climate data being used to inform the strategies?

Until now, water management decisions in NSW and across the Murray–Darling Basin have been based on adaptive management principles and on the historical record of climate conditions going back to the 1890s, about 130 years of rainfall, temperature and evaporation data. Concerns are growing that changes in climate arising from higher greenhouse gas emissions may make droughts more severe. There is also increasing evidence of longer droughts in the last millennium. Using a relatively short period of historical data alone provides only a limited understanding of extreme events.

New scientific methods have been developed that augment the historical record and provide a much-improved basis for characterising future climate risks to our ongoing water security.

To prepare the regional water strategies, the NSW Government has invested in new methods and data to develop a more sophisticated depiction of climatic conditions, including the likely frequency and duration of future droughts. This new data is created by integrating recorded historical data with paleoclimate data (data reconstructed from before instrumental records began, using sources such as tree rings, cave deposits and coral growth). Combining these two elements gives us 500 years of climate data.

We can then apply a stochastic modelling method (based on the statistical characteristics of the extended data) to get a dataset covering up to 10,000 years. This allows us to quantify the natural variability and extremes (drought and flood) in our regions since the last major global climate shift with more certainty than was previously possible. We have combined this with an understanding of key climate drivers and the use of existing climate projections to provide guidance on how natural climate variability and extremes may be influenced by future climate changes.

Bringing together climate variability data and climate change projections in this way greatly enhances our ability to identify plausible future climate impacts and risks. It represents a significant and important advance in water planning and management for NSW. It means that we have moved from making decisions that are heavily based on single ‘worst-case’ scenarios drawn from a short climatic record to a much more accurate understanding of extreme events, normal climate conditions and everything in between.

Why do we need new climate data; can’t we just use our historical measured data?

Our observed climate information (especially rainfall, temperature) has only been measured for about 130 years. Over this time, we have seen some droughts and wet periods. But those observations don’t tell us about all of the possible droughts or wet periods that we could experience in the future, only those that have happened in just 130 years.

Our new method adds 500 years of climate history to our knowledge by analysing things such as tree rings, river sediments and ice cores that have spent a long time in our landscape and carry tell-tale marks of events and changes in climate.This gives us a much better idea of possible climate patterns and variability in the future.

We also need to take account of possible changes to our historical climate patterns—even 500 years’ worth—due to climate change. The new method includes global and regional climate change projections.

Why do we need to consider climate change in the strategies?

Our regional water strategies firstly need to consider our knowledge of historical climate variability and what drives different patterns of variability. But under a changing climate, some of the drivers of our climate variability are changing and we need to also consider the influence and risks of such changes to our water availability.

The challenge in responding to climate change is that there are still uncertainties about how quickly changes will happen or what our responses might be to reduce the negative effects of any changes.

We need to understand how climate change might influence the risks to our water security and water availability in the future. We use the data from global and regional climate models to stress- test our water systems to see how they might be affected. We want to know the areas that could be the most vulnerable to climate change so we can focus on ensuring their future water security.

Does the new method mean we will run out of water sooner?

No, the new method only tells us what might happen under different scenarios of climate risk. This varies across different regions of NSW. More work is required to apply the new climate data to our understanding of groundwater systems to determine how secure groundwater supplies will be in the future.

Our new method indicates that the runoff that comes from rainfall and fills the dams may not happen as often, or we may not see the same amount of runoff as we currently do. Understanding this now means we can plan to deal with these situations should they eventuate. This might mean looking for alternative water supplies, changing how we use water, or looking at different ways of sharing the available water.

Why do we need models to understand our water security?

Models are tools that we use to understand complex systems. We can use them to simulate many different scenarios of climate risk and rapidly see possible outcomes.

Models are very useful for understanding huge amounts of data across long periods of time or for large areas. They can be tailored to specific NSW regions to give more detailed and relevant data.

But to be effective, models first need to be carefully set up and tested to check how good they are at predicting the measured data we already know (that is, 130 years of observed climate; 500 years of paleoclimate). We can then use them for forecasting the future climates we don’t know, including understanding long-term changes, or different scenarios of change.

What are global climate models?

Global climate models (GCMs) seek to represent the different physical processes of weather and climate. Building and running a climate model means representing physical processes using complex mathematical equations. Variables are then set to represent initial conditions and subsequent changes in climate. Powerful supercomputers then repeatedly solve the equations.

We can tell how good a GCM might be by seeing how well it describes historical and current weather and climate. They have proven to be effective at predicting temperature, and therefore evaporation, but there is much more uncertainty in predicting rainfall.

Global climate models predict the whole world, which means their predictions for regional and local climate is less precise. We use regional climate models to provide more detailed estimates of rainfall over different regions of NSW.

Why isn’t this modelling being incorporated into water sharing plans and water resource plans? 

Water sharing plans and water resource plans are currently based on historical climate records. The new climate modelling results are different to the historic climate records, and incorporating the new climate modelling into water sharing plans and water resource plans would be a significant change.

Before making such a change, we need to have an open and transparent conversation with the community about the merits of including the new climate modelling results in water sharing plans. We need to consider how that can be done, and the use of a risk-based approach. We need to be clear about the benefits and effects of allocating water based on likely future risks rather than historical drought scenarios, and what this will mean for towns, licence holders and the environment.

This government is committed to undertake this review as part of the Water Strategies program, and to considering how to use this to develop a new method for calculating allocations. However, this will take time, and significant community input about the level of risk for different categories of users. We want to understand the effects this could have on all parts of the community and the environment, we don’t want to rush and create new rules that could have unintended consequences.

Will this mean that the government will further reduce my licence reliability? 

Our new climate modelling results indicate that, with climate change, there may be more times when the amount of water we currently have available to share cannot meet all of the needs of water users. We need to plan for such times by considering alternative water supplies, changing how we use water, or looking at different ways of sharing the available water. Regional water strategies recommend projects or initiatives to help us plan for such times.

What does this mean for town water security?

The new climate modelling results indicate that NSW’s surface water supplies are likely to be less secure than we thought. This level of security varies across different regions of NSW. More work is required to apply the new climate data to our understanding of groundwater systems to determine how secure groundwater supplies will be in the future.

Our new method indicates that the runoff that comes from rainfall and fills the dams and rivers may not happen as often, or we may not see the same amount of runoff as we currently do. Understanding this now means we can plan to deal with these situations should they eventuate. This might mean looking for alternative town water supplies, changing how we use reticulated water, or looking at different ways of sharing the available water.

Why aren’t regional water strategies looking at downstream impacts?

We are making sure that upstream catchments are analysed to inform downstream catchment strategy development. For example, the Namoi, Gwydir and Border Rivers regions are being analysed first to ensure analysis for the Western regional water strategy includes any upstream considerations. Likewise, the upstream catchments are considering downstream impacts such as connectivity during their analysis.

How confident are you in these results? Why are you publishing these results if there is a level of uncertainty?

The global and regional climate models produce projections of what may happen in the future under a number of different scenarios. They cannot predict exactly what will happen.

We look at the results from a range of independent, global climate models to understand what each one means for how our current climate may change. We use the models that provide the best estimates (based on how well they simulate current climate) for different areas of NSW.

We apply how much we know about how climate varies across different parts of NSW to refine global climate data to use with regional climate models.

The global and regional models don’t give us one answer. Instead, they give us predictions that we can use to explore the range of changes likely to happen in the future. We cannot be sure of any of the predictions, but they do give us the best guide we have of future climate risk.

The new method for generating climate data provides us with a much better understanding of the range of climate patterns we are likely to see in the future, what the future climate risks are and what that means for NSW’s water security. It gives us more confidence in considering future climate risks to NSW’s future water security compared to only considering 130 years of climate records. In particular, we now have a better understanding of the probability of future extremes of droughts and floods.

As a result, we can now base our regional water strategies on more rigorous knowledge about the likely climate risks to our water resources.

What is paleoclimate?

Paleoclimate is an estimate of what the climate was like before recorded measurements of climate were taken. To go beyond our 130 years of climate records and build a paleoclimate record, scientists investigate things that have spent a long time in our landscape: tree rings, cave stalactites and stalagmites, river sediments, soil patterns, and ice cores.

Paleoclimate scientists study these items to find out responses to past climate, such as increased tree ring growth during wetter periods, or for ice cores, different concentrations of sea salt, depending on whether it was drier or wetter. Ice cores are usually obtained from areas on and around Antarctica, where research has shown strong relationships between Australia’s past climates and different characteristics of the ice.

Using paleoclimate research, we can extend our historical climate records to 500 years. We can then research the climate patterns over a much longer time period and investigate what may have caused these patterns. This helps us to better under possible future climate variability.

How sure are you of the accuracy of the paleoclimate records?

The paleoclimate records are used to help us understand patterns of past climate. For example, we can find out how long a drought has lasted in the past, and how often droughts occurred. We can look at the past climate from several hundred years ago to 1,000 years ago.

Researchers can then use paleoclimate records to see what it would might mean if our 130 years of recorded climate varied in the same way as patterns in the past.

Paleoclimate records are based on what we see between the landscape characteristics (such as tree rings, ice cores and river sediments) and climate, and come from a well-established and researched branch of the sciences. The records created from this research are not perfect, but the relationships used in the new method are the ones that we know are strong and relevant for NSW.

How can data found in ice cores in Antarctica tell us anything about climate in NSW?

Many ice cores have been taken and studied from an area of ice in Antarctica called the Law Dome Ice Sheet. It is around 200 km across and more than 1 km deep. Research has shown strong relationships between Australia’s past climates and different characteristics of this ice. Researchers measure the carbon dioxide and sea salt that is trapped and preserved within the ice.

Recent studies have shown that the Interdecadal Pacific Oscillation (IPO) has a strong influence on NSW’s climate. IPO describes swings in climate over a decade or more. During ‘negative phases’ of the IPO, the eastern Pacific Ocean tends to be cooler and wetter than average. During positive phases, the same regions tend to be warmer and dryer. The IPO influences the frequency of El Niño and La Niña events, and how severe they are.

Several scientific studies have shown that IPO also influences how much salt from sea spray is trapped in the ice. The ice cores provide a ‘lens’ in time where we can look back at how the sea salt concentrations varied over hundreds of years. This tells us how many time IPO cycles happened in Antarctica’s distant past. This matches IPO cycles in Australia, meaning we can then use the ice cores to tell us how climate patterns varied over NSW over the past 200 to 1,000 years.

Why have we used the driest climate change scenario?

The new climate data gives us with two datasets to improve our understanding of risk. The first is a generated 10,000-year record of streamflows derived from statistical analysis of our recorded climate and paleoclimate. This gives us a long-term understanding of streamflow behaviour under present-day climate conditions. The second dataset builds on this information, but introduces potential effects of human-induced climate change on our streamflows.

While there is a high level of agreement between many of the climate change models for temperature change, there is still a degree of uncertainty in relation to the modelling of future rainfall.

For the purpose of the draft strategies, one of the driest future scenarios has been chosen. Choosing the driest scenario gives us an idea of what the most extreme risks could look like and will help us stress-test the resilience of any identified options,

These driest, worst-case scenarios will not necessarily eventuate. There is a small probability that some of the extreme scenarios will occur. But they give us an opportunity to begin to plan for what we may need to put in place to protect water for critical human needs.

What can this new data be used for?

The new climate data has been developed to be used in river system models to compare the outcomes of policy, planning or infrastructure options. It can help us understand how effective a particular pipe, or dam or rule option will be in extreme scenarios relative to other options. That is, some options may be better able to sustain supplies through more intense, or more prolonged droughts, or may cope better with extreme flood events.

It is possible that the new climate data may be used for other purposes. For instance, the department is reviewing the useability of this new data within the existing guidelines for town water security assessments under the Safe and Secure Water Program.

What are the advantages and risks associated with using this data?

The new climate data gives us a much better understanding of the likelihood of extreme events such as drought occurring than has been available previously.

Modelling is a useful tool, but it is not a firm prediction of the future. In reality, if we experience extreme droughts, we will operate the system to prolong the availability of water for critical human needs.

This science still needs to be better understood and supported by the community. We need to explain how this science was developed, and how it can be used. We cannot make rushed decisions about how to use this information without a detailed and transparent conversation with the community. That takes time.

As a community, we still need to recognise that there is a very small risk of droughts and floods occurring that are more severe than the most severe events seen in the modelled information. For this reason, we need to move to managing the risks of these more extreme events, rather than managing one event, as has been done in the past. We need begin planning so we can be as prepared and resilient as possible for the next record-breaking drought.