Australia’s floods, aggravated by climate change, make history in Sydney

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A heavy weather system near Australia’s east coast has unloaded days of massive rainfall in the state of New South Wales, putting Sydney on track for its wettest year on record.

The torrents have triggered widespread flooding in eastern parts of New South Wales for the fourth time in less than 18 months. The flooding has triggered more than 100 evacuation orders.

Hundreds were saved when Sydney was hit by the fourth flood in less than 18 months

Since Friday, Sydney has observed 8.6 inches (220mm) of rain, while surrounding areas have seen far more – some approaching 28 inches (700mm) – about the amount London sees in a full year.

According to WeatherZone, an Australian weather information company, Sydney has accumulated in four days the same amount of rain it normally sees in a month and a half.

The city has recorded about 70 inches (1,769 mm) of rain this year, jumping 7.5 inches past 1890, the next wettest year as of July 4. And with almost five months of the year left, it was at least enough for his 11th wettest year since records began.

Around 200mm of rain has been recorded in many areas of Sydney over the past week.

Scientists attributed the excessive rainfall to a combination of factors:

  • The presence of several natural climate drivers: La Niña conditions, a periodic cooling of the tropical Pacific Ocean, are associated with increased rainfall in eastern Australia. A periodic cooling of the western Indian Ocean associated with La Niña is associated with increased precipitation in South Australia. A positive Southern Annular Mode causes easterly winds to bring moist air from the Tasman Sea to eastern Australia, which falls as rain.
  • Human-caused climate change warming the atmosphere and oceans and increasing precipitation events worldwide.

The Australia Bureau of Meteorology also found that warm ocean water helped intensify rainfall.

“During this recent rainfall event, very warm waters off the Australian coast (21-23°C) provided additional energy and moisture, contributing to the deep trough and east coast low, resulting in a relative 24-hour concentration of the heavy rains period,” she wrote.

The heaviest rain in New South Wales by Tuesday morning had fallen in Brogers Creek, about 65 miles south of Sydney, registering 36.7 inches (933mm). WeatherZone wrote that such rains have only a 1 to 2 percent chance of occurring in any given year. Brogers Creek has seen more in a month than Melbourne, Canberra, Hobart, Adelaide or Perth.

Darkes Forest, about 40 miles south of Sydney, recorded 27.4 inches (697mm) of rain.

Researchers say climate change is making the situation worse. Australia has warmed by about 2.6 degrees (1.5 degrees Celsius) since 1910. A warming atmosphere holds more moisture and can increase the intensity of extreme rainfall.

“Australia has long been a continent of drought and floods; However, projections suggest that climate change will increase this variability,” Chiara Holgate, a researcher at the Australian National University and the ARC Center of Excellence on Climate Extremes, said in an email. “Observations show that the intensity of heavy rain events in Australia has increased, including the short-lived events that may be associated with flash flooding.”

Holgate said Australia must prepare for more intense flooding events as flooding is one of the country’s costliest disasters. The February and March floods in south-east Queensland and New South Wales cost around US$3.35 billion in insured losses, according to the Insurance Council of Australia, making them the costliest floods in the country’s history.

“Major flooding poses a threat to water supplies and safe drinking water, and puts a strain on the operation of water treatment plants through increased sediment loads and potential pollutants,” environmental scientist Klaus Joehnk said in a press release.

Researchers have found that climate change has exacerbated several recent flooding events around the world. The World Weather Attribution Group found that May’s record flooding in Brazil, which displaced at least 25,000 people and killed more than 130, was exacerbated by climate change. The group also found that global warming led to torrential rains in South Africa in April that killed more than 400 people, twice as likely and 4 to 8 percent more intense.

On Tuesday, Australia’s Bureau of Meteorology tweeted that the major floods in parts of New South Wales continued, although they abated in Sydney. More than 20 alerts were active.

By Wednesday, the heaviest additional precipitation is forecast mainly north of Sydney, where the European forecast model is simulating up to 30 to 80mm of additional precipitation.