‘Rain bursts’ over Sydney have intensified 40% over last two decades, research finds

Rapid rain bursts over the greater Sydney region have intensified by at least 40% over the last two decades, new research shows.

Analysis of weather radar data by scientists at the ARC Centre of Excellence for Climate Extremes suggests that the intensity of rain bursts - extreme downpours that occur for a period of about 10 minutes - rose significantly between 1997 and 2018.

If the trend continues, it could pose challenges to Sydney's preparedness for future flash flooding, the researchers suggest.

The scientists measured rainfall using data from three overlapping ground-based radars at Newcastle, Terrey Hills and Wollongong, which together cover the greater Sydney region.

The radars estimated the rainfall rate in millimetres an hour, taking measurements every six to 10 minutes, the study's lead author, Dr Hooman Ayat of the University of Melbourne, said.

Also known as sub-hourly heavy rainfall, rapid rain bursts occur during the most intense part of storms and can increase the likelihood and severity of flash flooding, particularly in urban settings and steep mountainous regions.

"If this trend continues, we will have more-severe-than-expected flash floods in the future," Ayat said, adding that the rate of intensification was far greater than what was predicted with climate change. "At first we thought it was a problem with the data," he said.