The study only took place in the Sydney area, as those three radars had the longest period of data - back to 1996 in the case of Wollongong. The team believes they will find the same phenomenon elsewhere - they plan to study Darwin and Melbourne next, where there are radars with suitable amounts of data. But “that’s not to say we think we’ll necessarily find it everywhere”, Evans said.

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The study was led by Dr Hooman Ayat, now at the University of Melbourne, who described the intensification of rapid rain bursts as shocking and alarming.

“Previously, rain gauges, climate models and satellites have struggled to accurately identify rain bursts on such small-time scales,” he said. “However, our new data analysis technique was able to take historical weather radar data to get a much stronger picture.”

Professor Steve Sherwood, another member of the UNSW team, said the technique was now being used elsewhere around the world to make the most of radar data. “It’s a scientific mystery that we need more work on to understand better,” he said.

Some areas of Sydney are particularly susceptible to flash flooding, including low-lying parts of Marrickville and Wolli Creek along the Cooks River.

Evans said people ought to be prepared for more frequent flash-flooding, and the findings were cause to re-examine design standards for guttering and drainage.

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