Australia's rainfall events are already becoming more intense with climate change, raising the risks of flashflooding and potentially exceeding the nation's engineering codes, a new study finds.

While it's long been understood the atmosphere holds about 6.5 per cent more moisture per degree of warming, climate models have largely not captured the impact on individual storms, said Seth Westra, an associate professor at the University of Adelaide’s engineering school.

Intense rain events - an extreme example of which hit Toowoomba in Queensland in 2011 - are becoming more common, researchers say. Credit:Troy Campbell

"It's much more, two or three times the rate of that simple rule of thumb," said Professor Westra, who is one of the authors of the paper appearing in Nature Climate Change on Tuesday. "It's a really unique and alarming aspect of our conclusions."

The study examined rainfall records across Australia from 1966 to 2013 and identified an increase in the intensity of short-duration rain events "well outside the natural year-to-year variability you'd expect", he said. "In fact, they are more severe than climate models have been suggesting."