The Response of Land-falling Tropical Cyclone Characteristics to Projected Climate Change in Northeast Australia

The relationship between climate change and the intensity and frequency of tropical cyclones in the south Pacific is highly contested, particularly in the context of uncertainties surrounding the future of the El Niño Southern Oscillation regime (Chand et al. 2013; Diamond et al. 2013; Dowdy 2014). However, during the last two decades, the northeast coastal regions of Australia have experienced significantly increased total rainfall and more frequent heavy rainfall and intense tropical cyclone events (Alexander et al. 2007). In concert with rising sea levels, ocean warming, and ocean acidification, tropical cyclone activity and associated coastal flooding present the potential for increasing negative consequences for coral reef environments even with no change in frequency or intensity. Any possible future changes to tropical cyclone activity could exacerbate the impacts on reef and coastal environments. This study employs a numerical modelling approach to diagnose the response of tropical cyclone characteristics and associated coral reef damage potential in the context of projected climate change.

Using the National Center for Atmospheric Research Weather Research and Forecasting model (NCAR WRF; Skamarock et al. 2008) we simulate three intense tropical cyclone events that have affected the Queensland coastline during the last 5 years (Yasi 2011, Ita 2014, Marcia 2015) under current and projected future, 2070-2100, (RCP8.5) conditions. The RCP8.5 scenario is provided by an NCAR Community Earth System Model (CESM, Monaghan et al. 2014) realization. In response to this scenario, the tropical cyclone events increase in wind speed up to 20%, and increase in size by 20-35% compared to the simulations under current conditions. Further, the systems' central pressure is reduced by ~10hPa and critically this intensity is maintained longer in the life cycle, up to landfall. The future scenarios also result in the systems tracking further south and making landfall around 75-100 km further poleward. The increased size, intensity, and altered trajectory suggest that, under future climatic conditions, a wider extent of the Great Barrier Reef and coastal environment is at risk from amplified tropical cyclone damage when events occur, including locations that may be unaffected by intense storms in the current environment.

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