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Cross-Cutting Theme: Modelling

A challenge for managing Commonwealth environmental is how to apply our knowledge about individual sites or species to large spatial scales and whole ecosystems. Modelling can help us to do this by developing methods to model the response of aquatic ecosystems to Commonwealth water for the environment.  Work in this theme focused on developing solutions to issues associated with understanding how different species respond to flows, as well as creating the building blocks for a Basin-wide, multiple species model of response to water for the environment.

Image: Reed warbler in a wetland in the Murray catchment. Photo credit: Danial Stratford

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How does modelling assist in achieving water for the environment outcomes?

Modelling lets us take complex knowledge, and extend it to be relevant to the spatial and temporal scales at which management decisions need to be made – ultimately the whole of the Murray-Darling Basin.

Most managers and scientists rely on their own perceptions and experience when making decisions about water for the environment – we call this their ‘mental model’. These mental models provide individuals with expectations about how an ecosystem might respond to environmental watering, and what the risks and benefits might be. Different managers may, however, have different models. It can be difficult to identify cause-and-effect pathways, as the accuracy of mental models is difficult to assess.  Mental models also leave an organisation if individuals move on.

Using models can make knowledge transparent, so that it’s transferrable in space and time, and clearly identifies and reduces individual bias. Cause and effect pathways can be tested and used in adaptive management to improve both knowledge and management practice. This means that models provide an objective and repeatable assessment of the likely impact of a given management action, like environmental watering.

Models also provide us with the opportunity to run ‘what-if’ scenarios so that we can improve our understanding of, for example, the ecological response of different parts of the Basin to water for the environment under different climate scenarios.

Image: Flow-MER modelling team at work. Photo credit: Ashley Macqueen

Our approach

The approach we have used has expanded our understanding of individual species at specific locations, and at specific times, into a holistic assessment of the ecological response of the Basin to environmental watering. This work has provided the necessary building blocks to create a Basin-wide model of ecological response that is a powerful tool in quantifying the overall benefit of Commonwealth water for the environment in the Basin. 

One of the primary ways in which modelling has assisted the evaluation of Commonwealth water for the environment outcomes is by quantifying those outcomes. We already have models of hydrology (water movement), weather and other physical processes for the Basin. These models enable managers to understand the current physical condition of the Basin and, importantly, enable them to compare that to the condition that would be expected in the absence of water for the environment (the so-called ‘counterfactual’).

While models of many of the physical conditions in the Basin are well developed, there is no single model of ecological response at the Basin scale. Moreover, the effect of environmental water on ecological response depends on a range of environmental factors, in addition to the volume of water, and so can differ at different locations and times. This makes it extremely difficult for managers to create a holistic assessment of the change in ecological condition resulting from the use of water for the environment. 

This means that the benefits of Commonwealth water for the environment cannot currently be objectively quantified at the scales of many of the management decisions. Our work created an architecture for a Basin-wide ecological model that moves us closer to being able to understand the ‘ecological counterfactual’ for the Basin.  This gives managers a framework for quantifying the consequences of Commonwealth water for the environment.

A dry Narran River channel – upstream from Bangate Bridge – 7 December 2019. Photo credit: CEWH
Narran River flowing at ~2,500ML/d upstream from Bangate Bridge – 28 February 2020. Photo credit: CEWH

Activities & Outputs

We worked closely with several of the other Themes and Selected Areas to collate data and draw on their detailed knowledge. With them, we analysed data to capture specific responses to flow for our initial target species in our initial location. We collated broad-scale data from satellites and models to provide a foundation for our Basin-wide assessment of condition, and undertook modelling and analyses to understand species interactions and the links between condition in the Basin and the species that we selected.

We also worked with environmental water managers so that we could to understand what measures are most useful to them, and to ensure that our modelling outputs are aligned with management needs. We explored the value of a range of integrative variables and extrapolation measures. Throughout, we shared our learnings about how species respond, how such responses can affect other species, and how to use our detailed local knowledge to understand other times and places.

We undertook two closely-linked approaches:

Establishing relationships between ecological response and flow regime

We worked with the Basin Themes to provide robust analyses of data to understand and quantify the relationships (and uncertainty) between environmental outcomes and flow for aquatic ecosystems within the Basin. We then used this understanding to generate response relationships to describe and quantify potential ecological conditions as outcomes of the flow regime.

Understanding these relationships enabled us to apply this knowledge to new locations within the Basin, with or without Commonwealth water for the environment. This let us quantify outcomes in unmonitored areas and scale up to a Basin-wide understanding of the potential benefits of Commonwealth water for the environment.

For further information:

Repina & Stratford (2020) Sensitivity testing of an ecohydrological model for evaluating outcomes of environmental water.

Lloyd-Jones et al (2022) Modelling flow-ecology relationships for understorey vegetation across the Murray-Darling Basin.

Stony creek frog (Ranoidea (Litoria) wilcoxii) in the upper catchment of the Condamine river. Photo credit: Danial Stratford

Developing model architecture to integrate the outcomes across themes

This research collated remotely-sensed data (e.g. from satellites) along with existing models (e.g. of water movement and soil moisture) to get a Basin-wide assessment of physical condition. We used this to develop relationships with species responses to environmental watering. This was based on times and places where we have the best knowledge, considering other factors that mediate the response to flow, such as local weather and land use.

A key challenge was to understand how the response of one species may influence the response of another species (e.g. increased fish abundance as a result of environmental watering providing more food for fish-eating birds). Initially, we focussed on a few species for a single well-studied site, then we expanded our assessment to other similar sites and to incorporate more species.

For more information:

Holt G, Macqueen A, Lester RE (2023) Integrative modelling framework to evaluate multi-scale impacts of environmental watering.

Nankeen night heron in a wetland in South Australia. Photo credit: Danial Stratford

Image: Refuge pool in the Darling River during low flows. Photo credit: Danial Stratford

Our team

Dr Danial Stratford

Danial is an aquatic ecologist and ecological modeller with CSIRO Land and Water in the Modelling Water Ecosystems team with a background in modelling the environmental outcomes resulting from changes in flow regimes. He has a broad range of experience from within the Murray-Darling Basin, northern Australia and internationally, and has delivered to a range of stakeholders and clients. Danial uses a range of approaches and draws upon skills in statistical analysis, statistical modelling and mechanistic modelling to understand, quantify and predict the environmental outcomes of flow events, flow sequences and flow regimes. He specialises in understanding temporal dynamics and scenario analysis, linking hydrological data to quantify environmental outcomes under uncertainty. The core of Danial’s work is to deliver products and knowledge to improve the environmental outcomes associated with water management at a range of spatial and temporal scales.

Associate Professor Rebecca Lester

Rebecca is an ecologist with experience in freshwater, estuarine and marine systems.  She has wide-ranging research interests, but is primarily focused on the management of aquatic ecosystems and in achieving good ecological outcomes in systems that involve multiple uses and commercial industries.  She combines her expertise in ecology with a solid background in hydrology and erosional processes and actively collaborates across biological and other disciplines. She has a broad range of analytical and modelling skills and specialises in combining data about a range of physical and biological processes into a broader understanding at an ecosystem scale, giving her the requisite skills to participate in this project. For more information, visit qael.org.

Dr Galen Holt

Galen is an ecologist and postdoctoral research fellow at Deakin University. He is interested in the large-scale responses of species and communities to environmental conditions at large spatial and temporal scales. Of particular interest is how rigorous, process-based understanding of large-scale ecological outcomes can inform management decisions. His background is primarily in aquatic community ecology, where he studies how species and communities respond to varying environmental conditions in space and time. His research encompasses empirical studies of aquatic insects, statistical analyses, theory, and development of large simulation models. He takes a varied modelling approach, ranging from quite generic models to understand fundamental ecological processes, to the development of models incorporating empirical data to capture dynamics of specific communities with targeted management goals. For more detail, visit qael.org.

Dr Luke Lloyd-Jones

Luke is a CSIRO Research Scientist with DATA61. Luke is an applied statistician with experience in applications in ecology, fisheries, and human genetics, including very large and complex datasets. He focuses on the development and implementation of novel statistical and machine learning methods and provides high-level analytical and statistical modelling expertise for the vast amounts of interesting data being generated by the CEWH waterbird movement tracking project and also contributes to reporting and manuscript preparation.

Dr Ashmita Sengupta

Ashmita is a Senior Research Scientist at Land and Water CSIRO and ecohydrologist with expertise in optimization, adaptive management of water resources geared to protect ecosystem health, sustainable low impact development design, and system vulnerabilities under climate change and other pressures.

Ashley Macqueen

Ashley is an aquatic ecologist and a postdoctoral research fellow at Deakin University. His work focusses on drawing together diverse datasets and models in novel ways to create tools that are underpinned by core ecological principles and inform the management of aquatic systems in Australia and abroad. For more detail, visit qael.org.

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