Since Friday, Sydney has observed 8.6 inches (220 mm) of rain, while surrounding areas have seen far more — some approaching 28 inches (700 mm) — which is around the amount London sees in an entire year.
Sydney amassed the same amount of rain over four days that it typically sees in a month and a half, according to WeatherZone, an Australian weather information company.
The city has registered about 70 inches (1,769 mm) of rain this year, leaping 7.5 inches past 1890, its next-wettest year through July 4. And, with nearly five months of the year still to go, it has already clinched at least its 11th-wettest year on record.
Another 73 mm over the last 24 hours brings #Sydney‘s running annual total up to 1769 mm. Not only is this Sydney’s wettest year-to-date on record by whopping 191 mm (above 1578.3 mm from 1890), this is also ALREADY the city’s 11th wettest year in records dating back to 1859. pic.twitter.com/JvZjIgTrew
Human-caused climate change, which is warming the atmosphere and oceans and intensifying precipitation events globally.
The Australia Bureau of Meteorology also noted that warm ocean waters helped intensify rainfall.
“During this recent rainfall event, very warm waters off the Australian coast (21-23°C) provided extra energy and moisture contributing to the deep trough and east coast low, leading to the relative concentration of the heavy rainfall to one 24-hour period,” it wrote.
Although many areas of Sydney recorded about 8 inches (200 mm) of rain over the past week, the heaviest amounts in New South Wales had fallen in Brogers Creek, about 65 miles south of city, where 36.7 inches (933 mm) fell. WeatherZone wrote that such rainfall has just a 1 to 2 percent likelihood of occurrence in any given year.
The 933mm of rain that fell at Brogers Creek, NSW during the last four days has an Annual Exceedance Probability (AEP) of 1 to 2%. This is statistically a 1 in 50-to-100 year rain rate for this location.
Darkes Forest, about 40 miles south of Sydney, posted 27.4 inches (697 mm) of rain.
Researchers say climate change is worsening the situation. Australia has warmed by around 2.6 degrees (1.5 Celsius) since 1910. A warming atmosphere holds more moisture and can increase the intensity of extreme rainfall events.
“Australia has long been a continent of droughts and flooding rains; having said that, projections indicate that climate change will supercharge this variability,” Chiara Holgate, a researcher with the Australian National University and ARC Center of Excellence for Climate Extremes, said in an email. “Observations show there’s been an increase in the intensity of heavy rainfall events in Australia, including the short-duration events, which can be associated with flash flooding.”
Holgate said Australia needs to prepare for more intense flooding events, as floods are one of the most expensive disasters the country faces. Flooding in southeast Queensland and New South Wales in February and March cost about $3.35 billion in insured losses, according to the Insurance Council of Australia — making it the costliest flood in the country’s history.
“Large floods are a threat to water supply and safe drinking water, straining water treatment plant operation by increased sediment load and potential contaminants,” environmental scientist Klaus Joehnk said in a news release.
Researchers have found that climate change has exacerbated several recent flooding events around the world. The World Weather Attribution group found that record flooding Brazil in May, which displaced at least 25,000 people and killed more than 130, was exacerbated by climate change. The group also found that global warming made torrential rains in South Africa in April, which killed more than 400 people, twice as likely to occur and 4 to 8 percent more intense.
On Tuesday, Australia’s Bureau of Meteorology tweeted that major flooding was continuing across portions of New South Wales, even as it eased in Sydney. More than 20 warnings were active.
Through Thursday, the heaviest additional rainfall is projected mainly north of Sydney, where the European forecast model simulates up to 1 to 3 inches (30 to 80mm) of additional rainfall.