Understanding cyclones: science to protect our reef

October 25, 2022

Global projections show there’ll be fewer but more intense tropical cyclones on average in northern Australia. What does this mean for our reefs?

New research has looked at the potential for downscaled tropical cyclone projections to be used in management decisions for individual reefs.  

No matter what our future warming, tropical coral reefs will be exposed to damage from tropical cyclones. Cyclones have a myriad of impacts on our reefs, heavy rainfall can cause flooding, reducing salinity and increasing nutrient and sediment run off all of which can impact coral health.

But it’s wave damage that has the potential to cause the most severe damage to coral reefs. Intense waves can break apart the physical structure of our reefs which can then take decades to centuries to recover. The worst wave damage comes from intense, large, and slow-moving cyclones that persist near reefs.

Hub researcher Hamish Ramsay collaborated with the University of Leeds, University of Queensland, and the Australian Institute of Marine Science to investigate the potential of climate models as a tool to understand the key characteristics of cyclones that influence wave damage to inform management of these important ecosystems. Until now, there hasn’t been an assessment of the ability of climate models to simulate cyclone tracks at a smaller spatial scales relevant for these types of management decisions.

Can climate model projections help target reef management?

Projections at global or ocean-basin scale indicate a future decrease in the number of tropical cyclones in northern Australia, but an increase in the proportion of high intensity storms. What is less certain is how well downscaled cyclone projections from global climate models represent cyclone characteristics that determine impacts at reef scale, for example size and speed of the cyclone, and the duration in any one place. There is also uncertainty of how well downscaled cyclone projections  replicate historical cyclone tracks at smaller scales, for example individual reefs.

The cross-disciplinary team looked at whether climate models can be used to predict localised damage to tropical reefs from cyclones. The study focused on tropical north Australia and examined how well simulated historic downscaled tropical cyclone tracks captured the key characteristics which drive a cyclone’s potential to damage individual reefs. In order to understand potential future cyclone induced damage to coral reefs, the study then considered how well the models simulated the occurrence of these key characteristics for past events compared to future climates under the high-emissions scenario. The results found some models project a future increase in cyclone characteristics that cause reef damage, and others projected a decrease. There were also regional differences in how well the simulated tropical cyclones captured observed cyclone characteristics. Simulations for the Great Barrier Reef represented observed cyclone characteristics well but other case study areas in Northern Territory, the Coral Sea and Western Australia showed poor-to-mixed results. This mixed result is partly because climate models are not able to accurately represent the historical locations of cyclone tracks at finer spatial scales, for example where they would track over  individual reefs.

Improving reliability of fine-scale processes

Researchers acknowledge that climate models are not yet reliable enough to simulate localised factors most damaging to reefs. Regional differences in cyclone intensity projections is a topic of on-going research. Further research that uses explicitly-simulated tropical cyclones generated from global climate models is recommended to improve these uncertainties.

The Climate Systems Hub project Regional climate change guidance for local action will look at improving methods for representing key physical processes in models, such as wind, for hazardous phenomena including tropical cyclones. Hub researchers are using multiple lines of evidence, including different downscaling methods, to inform regional extreme weather projections. This will help improve the representation of hazardous phenomena at local scales in climate models. The Climate Systems Hub is also building on and updating the ESCC Hub Tropical Cyclone Projections portal with new projections using the most recent CMIP6 global climate models. New analysis of tropical cyclone projections will include detailed regional changes and extreme wind gust probabilities for key regions, and analysis of tropical cyclone risk to the Great Barrier Reef.

The Hub will continue collaboration through project Regional climate change guidance for local action to improve the relevance of climate projections, data and information for the use in the management of Australia’s coral reefs

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