精东传媒

Greater Sydney had its wettest July on record according to the Bureau of Meteorology, recording around double the average rainfall for winter. And the rain isn鈥檛 set to slow down anytime soon, according to Dr George Takacs, Honorary Senior Fellow in the UOW School of Physics. 

鈥淭his year is shaping up to be the wettest on record in much of southeastern Australia,鈥� he says.  

There are three major drivers of rainfall changes: the El Nino Southern Oscillation (ENSO), Indian Ocean Dipole and the Southern Annular Mode. These three patterns have combined over recent years, causing extensive rain across the east of Australia.  

鈥淲hen the ENSO is in a La Nina phase, we get higher than average rainfall in eastern Australia. When the Southern annular mode is in a positive phase, likewise,鈥� says Dr Takacs. 

鈥淭he Indian Ocean Dipole is also in a negative phase which brings higher than average rainfall to southeastern Australia. It is extremely rare for all these three drivers to be simultaneously in a phase which brings higher rainfall.鈥�  

It is the third year in a row of La Nina, the phase of ENSO which causes stronger winds blowing east to west across the Pacific Ocean.  

鈥淲hat happens in a La Nina, is there is an overall transfer of energy from the atmosphere to the oceans, so global average atmospheric temperatures are lower than they would otherwise be. The opposite applies to El Nino years, during which there is a transfer of energy from the oceans back to the atmosphere, raising atmospheric temperatures,鈥� says Dr Takacs. 

鈥淟a Nina leads to warmer than usual waters off the east coast of northern Australia. In turn this means more water evaporating into the atmosphere, which then gets directed upward over land and condenses as rainfall. 

鈥淚t is unusual to have La Nina three years in a row, as we have had recently. Normally the time between one La Nina to another is around three to eight years.鈥� 

_{Dr George Takacs, from the UOW School of Physics}

The ongoing effects of climate change 

It isn鈥檛 just the coincidence of these weather patterns causing major disasters. Recent data has shown in the Arctic and Antarctic. Dr Takacs says the rapid heating of the poles, faster than the rate of the equator, can contribute to the natural disasters we have seen in recent years.   

鈥淲hat creates, but also disrupts, our large-scale weather systems is the difference in temperature between the equator and the poles. As that temperature difference decreases, these systems may become more persistent. So long dry spells and heatwaves will become more frequent, which is going to predispose us to bushfires, but also long wet spells become more persistent and they're going to predispose us to floods and landslides.鈥�  

Not only will these disasters become more common, Dr Takacs says the geographic extent of such events continues to grow.  

鈥淭he areas that were affected in the [Black Summer] bushfires in Australia, that was unprecedented. Likewise in these floods 鈥� normally if it was flooding on the south coast in Moruya, it wouldn鈥檛 be flooding in places like Bellingen or the Lockyer Valley in Queensland at the same time. The worry is the emergency services have to respond to a large number of places, but there isn鈥檛 the capacity,鈥� he says.  

鈥淚t is unknown whether we will continue to have wetter summers in the future. While global warming is reducing the temperature difference between equatorial and polar regions, how our climate system operates is entering unknown territory. We need to prepare now for greater variability.鈥� 

Dr Takacs will be speaking alongside other climate experts in a special webinar for Global Climate Change Week. This event is free and available to the whole community, however registration is essential.