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Models

The marine modelling component of eReefs was tasked to deliver numerical models capable of simulating and predicting the physical hydrodynamic state, sediment transport, water quality and basal ecology of the Great Barrier Reef lagoon and reef matrix. Together, these models represent a capability to simulate the transport and fate of waterborne material, of either oceanic or terrestrial origin, and its impact on Reef water quality.

The eReefs regional and relocatable models include hydrodynamic, sediment, wave and biogeochemistry models for the Great Barrier Reef ecosystem. Some examples of products available from these model systems are shown below.  See Model Outputs for further examples and about the models for more details. The Executive and Technical summaries from the model technical report can be accessed via the following links:

eReefs models Executive summary (6 pages)

eReefs models Technical summary (5 pages) 

The full model technical report and associated appendices can also be downloaded at the bottom of the page.

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True colour image from GBR1:  The animation moves northward from the southern end of the GBRMP.  Black is land, yellow is river sediment, dark green is CDOM and green-blue is phytoplankton.

The 2016 Coral Bleaching Event captured by the eReefs modelling suite

During the summer of 2015/16, the Great Barrier Reef suffered its worst bleaching event in recorded history. The eReefs modelling suite quantified the thermal stress on the corals reefs with unprecedented temporal and spatial resolution.

The first figure represents a snapshot of the bleaching event and the following animation represents the lead up to the event

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Thermal stress on corals from 1 Dec 2015 – 31 March 2016 as quantified by Degree Heat Weeks (DHWs) by the 4 km resolution GBR-wide model (GBR4, left hand side) and at each of the 30 individually-resolved ~200 m resolution Relocatable Ocean Models (RECOM, right hand side). Degree Heating Weeks is the cumulative sum of the degrees above the seasonal mean multiplied by the duration of weeks. Thus 1 degree above the seasonal mean for 2 weeks gives DHW = 2 C week. On GBR4 the DHW is an average of the top 17 m of water; for the individual reefs it is calculated at the seabed. The individual reefs are magnified ~200 times, and are aligned vertically by their latitude with the GBR-wide model on the left, and horizontally by their distance from the coast.

dhw_new

The animation shows the GBR-wide trend in thermal stress with the warmest waters in the north and closest to the coast. These GBR-wide trends are seen across the individual reefs, with processes such as tidal currents, wind-driven vertical mixing, local circulation, and lagoon heating and cooling adding further spatial variability.

The simulations finish on 31 March 2016 at approximately the maximum cumulative thermal stress across the individual reefs over summer, a strong indicator of both coral bleaching and bleaching mortality. One observational metric use to quantify the severity of bleaching of particular reef is the percent area bleached. The greater the percentage of the reef bleached, the less resilient this individual reef is to bleaching. By producing high-resolution spatial maps of individual reefs, the model quantifies the percent area of a reef over a DHW threshold of 14 C week that is known to lead to high mortality. We are presently working with our colleagues at AIMS to compare the model-generated DHWs in the above figure with the observed severity of bleaching from the 2016 event. The labels S, Maj, Mod and Min give the AIMS assessments of the reefs at the send of the summer.

The present suite of high-resolution models of individual reefs provides the best opportunity to quantify the relative vulnerability of hundreds of unobserved reefs to the climatic conditions of 2016. Further simulations, run for past summers, and for predictions of future climatic conditions, can be used to quantify the resilience of individual reefs for the envelope of future conditions that the GBR is likely to face.

RECOM Coral bleaching event team: Mark Baird, Elisa Elofer, Marion Mengin, Mike Herzfeld, Farhan Rizwi

What we’ve produced

The raw eReefs model data is available through this website (Access to raw model output) or via THREDDS server: Access to raw model outputs via THREDDS server on NCI

The RElocatable Coastal Ocean Model (RECOM) developed under eReefs is functional and can be demonstrated in a CSIRO development computing environment. After consultation with stakeholders, a deployment strategy will be implemented after which RECOM will be publically accessible.

Currently, there have been 21 eReefs related papers published in peer-reviewed journals, and eReefs material has been presented at 27 international and national conferences, workshops and seminars. Since there remains a wealth of information residing in the eReefs archive yet to be explored, this list will undoubtedly grow. Many of these publications relate to state-of-the-art development that occurred during the eReefs project, and this development is a significant achievement in its own right. These enhancements notably include advances in data assimilation, open boundary conditions, transport models, optical models, carbon chemistry and inclusion of the impacts of Trichodesmium on nutrient budgets. These developments are transportable to other applications. RECOM was associated with significant development, and currently lies at the forefront of automated relocatable modelling systems; to our knowledge it is the only model of its kind capable of simulating hydrodynamics through to biogeochemistry with its advanced level of automation.

Operational considerations

The eReefs marine models are suitable for, and currently performing in, near real-time operation. The infrastructure that supports the near real-time operation has now been functioning for multiple years and is considered robust. There is a commitment by CSIRO to continue to operate these models on an on-going basis, and provide outputs to the wider community at various levels ranging from snapshots and animations of key variables, value added products based on these key variables, web enabled exploration of the raw data and access to the raw data itself. Many of these model-based products and data access and integration tools are being developed through other eReefs projects. The on-going operation of the modelling suite and provision of data products will require resourcing, and the level of resourcing will be dependent on the uptake and demand for eReefs products. Currently the commitment is to make the eReefs outputs available and rectify any downtime in a reasonable timeframe within business hours (Mon-Fri, 9-5). Reasonable user requests will be facilitated along similar lines.

 

The full model technical report and associated appendices can be downloaded here

Link to eReefs model Technical Report (497 pages 145MB)

Download Appendix A: eReefs Biogeochemistry configuration and model assessment 47.1 MB

 

Appendix B: Biogeochemical model description (3 MB)