SINGAPORE – Climate change is fuelling the weather causing severe floods in Sydney, scientists say, and as the planet heats up, more damaging flooding events in Australia – and elsewhere – can be expected.
The present floods, the third and heaviest this year to inundate parts of Sydney, have been linked to La Nina, a naturally occurring Pacific Ocean climate pattern that typically brings wetter weather to eastern Australia and South-east Asia.
But climate change is causing La Nina’s impacts to become more severe, scientists say. Similarly so for El Nino, the flip side to La Nina, which usually triggers hotter weather and drought in Australia and South-east Asia.
“In a warming planet, there is more moisture in the atmosphere. So when it rains, more water comes down with it,” explained Dr Agus Santoso of the Climate Change Research Centre at the University of New South Wales in Sydney.
“Climate change is exacerbating the effect of La Nina. Our research suggests that climate change increases the frequency of strong La Nina events. However, even if La Nina events themselves do not change, the impacts are expected to be more severe. The flooding events that are currently unfolding may be a reflection of that,” he told The Straits Times.
La Nina causes the large-scale cooling of surface temperatures in the central and eastern equatorial Pacific Ocean that occurs every two to seven years. The present La Nina episode started in 2020 and continued largely uninterrupted until June this year, when Australia’s national weather agency, the Bureau of Meteorology, declared the event over but gave it a 50-50 chance to re-form later this year.
Even as the influence of the present La Nina wanes, another weather phenomenon is set to bring more rainfall to South-eastern Australia in the coming months – a negative Indian Ocean Dipole (IOD).
During this periodic event, the eastern Indian Ocean is warmer than normal and the western Indian Ocean near Africa is cooler. This causes more moisture-filled air to flow towards Australia and south-east Asia. The weather bureau said a negative IOD increases the chances of above average rainfall from June to November for much of Australia.
Conversely, positive IODs have the opposite effect. A strong positive IOD was partly to blame for severe drought across eastern Australia in 2019 that fuelled record bush fires.
With so much rain over the past two years, catchments are saturated. But planning authorities have also made things worse by allowing continued urban expansion into flood plains in Sydney and elsewhere, putting thousands of homes at risk.
This has increased the need to try to reduce the impacts of floods, tackling the urban sprawl and building higher bridges and other flood defences.
“The repeated flood events across the Australian east coast foreshadow a future of wild weather, disruption and loss unless we act now,” said Professor Mark Howden, director of the Institute for Climate, Energy & Disaster Solutions at The Australian National University in Canberra.
“Without a clear plan to confront global warming and its impacts, we can expect this disruption to ramp up over time,” he said in a commentary on Tuesday (July 5) in The Sydney Morning Herald.
