The floods that devastated the east coast of Queensland and New South Wales in February and March were of an unprecedented nature. The amounts of rain that fell in a short period are staggering, causing devastating floods in entire communities and the death of 22 people. The road and bridge repair bill alone is expected to be $1 billion, not to mention homes, public facilities, farms, businesses and infrastructure.
The Climate Council has estimated that the flooding event will be the worst on record. He concluded that weather conditions previously described as extreme and supposed to occur once every hundred years are now occurring more frequently.
Climate Council scientist Professor Will Steffan told the Australian Broadcasting Corporation (ABC): “The fact is we have extreme events more often. “Ordinary” extreme events are now occurring in quick succession. »
Rainfall totals from 9 a.m. Feb. 24 to 9 a.m. Feb. 28 at three weather stations give an indication of the colossal amount of precipitation. Mt. Glorious, an area of rainforest, located 84 kilometers northwest of Queensland’s state capital, Brisbane, saw the highest amount of 1,637mm, while Pomona 135 kilometers north of the capital had 1180 mm and Bracken Ridge an outer suburb of Brisbane experienced 1094 mm.
Brisbane recorded 677mm over three days, a three-day record. Northern New South Wales (NSW) experienced torrential rains and similar flooding. In the town of Lismore in northern New South Wales, the state emergency service was overwhelmed within minutes. He was unable to respond quickly to calls, crippled by a lack of personnel and the availability of only two boats to cover a city of 44,000 people. Over 14,000 homes were destroyed.
In Sydney, the state capital of NSW and Australia’s largest city, the worst affected areas were the city’s southwestern working-class suburbs, affecting more than 60,000 people.
Several climatic phenomena merged to lead to the extreme weather event. The immediate cause of the rainfall is an extremely slow-moving low pressure system which has drawn moist air from the Coral Sea onto Australia’s east coast, dumping its enormous water content over a limited geographical area. The media called the phenomenon a “rain bomb”.
Nina Ridder, research associate at the Center of Excellence for Climate Extremes, told the new scientist that “because it moves so slowly (weather system) – it’s essentially stationary – it dumps all the water it has on the same area.”
Although it is difficult to determine the exact contribution of climate change to specific extreme weather events, scientists draw general conclusions.
According to the Vice-Chair of the Intergovernmental Panel on Climate Change (IPCC) and Director of the ANU Institute for Climate, Energy and Disaster Solutions, Mark Howden, the climate crisis was “built into this event “.
The latest IPCC report on climate change was released on February 28, predicting that rising atmospheric and sea temperatures will lead to increased storm intensity.
“One of the clear projections is an increase in the intensity of heavy rainfall,” said coordinating lead author of an Australia-New Zealand chapter of the IPCC report, Brendan Mackey.
Scientists predict that the atmosphere will retain 7% more moisture for each degree of increase in atmospheric temperature, leading to heavier rains and more extreme flooding. Increasing ocean surface warming increases evaporation, delivering greater amounts of moisture into global weather systems. The average atmospheric temperature in Australia has increased by 1.4℃ since records began in 1910.
“Current ocean temperatures around eastern and northern Australia are about 1℃ warmer than the long-term average, and nearly 1.5℃ warmer than average off the coast. NSW”, Joëlle Gergis, lecturer in climate sciences at the Australian National University (ANU), indicated in the Conversation.
Climate change is mainly caused by the burning of fossil fuels such as coal and oil producing greenhouse gases including carbon dioxide and methane. It is often difficult to determine precisely how this affects the complex and interacting factors that determine Australian weather patterns and therefore extreme events.
One of the most important drivers of Australia’s weather systems involves variations in ocean surface temperatures in the Pacific, Indian and Southern Oceans. A significant factor is El Niño–Southern Oscillation (ENSO), currently in the La Niña phase. ENSO is associated with the variation in wind and ocean temperatures in the eastern Pacific Ocean. La Niña is generally associated with low surface atmospheric pressure over mainland Australia and therefore wetter weather conditions. the 2010-2012 La Niña was associated with the wettest two-year period on record up to that time, including flooding on Australia’s east coast and Brisbane.
University of NSW oceanographers who studied these floods found that it was likely that climate change made the heavy rains worse during this La Niña event. Gergis explained that “their analysis highlighted how long-term warming of the oceans can alter rain-producing systems, increasing the likelihood of extreme rainfall events during La Niña events.”
Other important factors contributing to the current extreme precipitation events are the negative Indian Ocean Dipole (IOD) and a positive Southern Annular Mode (SAM). The IOD is a sea temperature difference between two poles in the Arabian Sea and the eastern Indian Ocean south of Indonesia. This is known to affect rainfall patterns in Australia and neighboring countries. In its negative phase, it is associated with cooler sea surface temperatures and is known to cause more precipitation in northern and southern Australia.
The Southern Annular Mode (SAM) refers to strong westerly winds that blow almost continuously in the middle to high latitudes of the Southern Hemisphere. These winds move west to east and are known to bring rainfall to southern Australia. In its positive phase, the winds contract towards the South Pole, which increases the chances of summer rains in southwestern Australia.
Since the 1980s, climatologists have warned that due to global warming, extreme weather events will increase in frequency. Australia has been periodically devastated by extreme weather over a long period, including record drought, devastating bushfires and flooding. Although they have occurred throughout history, these phenomena have been exacerbated by climate change, causing an increasing series of devastating climatic events.
The Millennium Drought of late 1996 to mid-2010 was part of a long-term drying trend that has persisted for more than four decades. It affected the Murray-Darling Basin and most state capitals across the country. This caused the northern subtropics of Australia to experience higher monsoon rainfall. This was driven by a very strong El Niño phase.
In 2009, the state of Victoria was devastated by bushfires which killed 173 people. The millennial drought ended with the double La Niña of 2010-11 and 2011-12. This was accompanied by flooding in Queensland, NSW and Victoria in 2010-11. In 2013 there was significant flooding in New South Wales and Queensland due to Cyclone Oswald.
David Karoly, honorary professor in the School of Geography, Earth and Atmospheric Sciences at the University of Melbourne, told the Australian Broadcasting Corporation (ABC) that climate change and the onset of La Niña are likely to have contributed to the increased risk of heavy rain in southeast Queensland. in the current event.
“The difficult part is to precisely quantify the increase in risk or the contribution to the amount of precipitation, both of which are uncertain,” he said.
Researchers continue to look more closely at the links between climate change and the drivers of extreme weather events in Australia.
Wenju Cai, Director of Southern Hemisphere Ocean Research at the Commonwealth Scientific and Industrial Research Organization (CSIRO), and his team published a paper in August 2021 titled “Changing El Niño–Southern Oscillation in a warming climate”. He looked at the ENSO events of the 1950s and compared them to the climate indicated by the geological record. Their modeling implied “that ENSO would become more unstable and favor larger amplitude events under warming.”
A study by John Fasullo, project scientist at the Climate and Global Dynamics Laboratory, and associates entitled “ENSO’s Changing Influence on Temperature, Precipitation, and Wildfire in a Warming Climate” also found that the effects of ENSO would be amplified in the event of global warming. Looking at the impact of El Niño, which is the opposite of La Niña, they predicted that the worst impact would be felt in the United States and Australia with increased impact from bushfires or wildfires and extreme temperatures.
Based on the study, Fasollo told the Guardian“We can say that an El Niño of a given magnitude that forms in the future is likely to have more influence on our climate than if the same El Niño had formed 50 years ago.”
Australian politicians have tried to blame the current flood crisis on processes over which they have no control. New South Wales Liberal premier Dominic Perrottet described the flood as a “once in 1,000 year event”, while Queensland’s Labor premier Annastacia Palaszczuk said “I can’t do anything against mother nature.”
While tremendous natural forces are at work, governments have done little or nothing to prevent floods, implement flood prevention and mitigation measures, ensure the availability of needed emergency services, or fund the necessary aid and reconstruction.
At the same time, governments in Australia, like those around the world, have ignored warnings from climate scientists and refused to implement policies to halt and reverse climate change. Their cosmetic measures will only ensure that extreme weather events, including droughts and floods, will become more frequent and severe in the future.