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Extreme weather

Using NCI’s Raijin supercomputer, researchers from CSIRO, the ARC Centre of Excellence in Climate System Science, together with collaborators from China, India and Japan, have predicted that natural disasters could triple in frequency over the coming century.

Dr Wenju Cai and his team used computer modelling to analyse, for the first time, the effect of rising greenhouse gas emissions on the Indian Ocean Dipole (IOD) weather system.

The study, published in Nature, suggests that the frequency of bushfires, floods and drought in Australia will change from one event every 17 years in the 20th century to one every 6 years in the 21st century.

“Positive IOD events occur when the eastern Indian Ocean sea surface temperature is cooler than normal and the western, tropical Indian Ocean is warmer than normal,” Dr Cai explains.

“During extreme positive-IOD events, the winds along the Indian Ocean equator become stronger. This leads to catastrophic floods in Africa, but devastating droughts in Indian Ocean rim countries, including Australia.”

Dr Cai said the Indian Ocean Dipole is linked to the Black Saturday bushfires of 2009.

“In Australia, we have bushfires every summer, but if there is a positive IOD event in the previous Spring and Winter, causing less rainfall and higher temperatures that build up fuel, we tend to have bushfires that are more severe.

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“We saw three consecutive years of positive IOD events leading up to the Black Saturday bushfires. In 2006, 2007 and 2008 we had very dry Springs and Winters – we were in the gut of drought. The conditions were so dry, the bushfire could move very fast.

“In fact, most of our major bushfires were preconditioned by a positive IOD event in the preceding seasons.”

Positive IOD events are likely to become much more likely as rising CO2 levels affect the distribution of heat, says Dr Cai.

“Normally along the equator the wind blows from Indonesia to the western pacific. But this wind is weakening because higher CO2 levels in the atmosphere means the atmosphere can hold more and more water at a higher temperature.”

This change in wind patterns means the eastern Indian Ocean is warming less quickly than the western Indian Ocean, creating a more pronounced temperature gradient and more extreme IOD events.

Dr Cai says this research couldn’t have been done without high-performance computing environments such as NCI.

“This sort of work relies on a lot of analysis and calculation using computational facilities. This model data is openly available to every scientist around the world. We’re leading the world in this area of research and that is in large part due to the efforts and care of the very dedicated team at NCI.”

This is the 4th Nature paper the team has published, with another due out later this year. 

Read the paper.

 

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