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.

"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."

"The sorts of rates that engineers have been using [for these events] are lower than the historical changes that we're observing in this study," Professor Westra said, adding that engineering codes may need to be updated to recognise "more radical rainfall" events in the future.