Australian storms that occur at warmer temperatures have more intense highs and weaker lows in rainfall, according to a paper published online this week in Nature Geoscience. If this trend continues with future warming, the risk of flooding due to short-term extreme bursts of rainfall could increase even if the overall amount of precipitation associated with each storm remains the same.

Heavy precipitation events are thought to become more frequent and more intense with rising temperatures. However, changes in the distribution of rainfall over the course of a storm event had not been noted.

Ashish Sharma and Conrad Wasko compiled measurements of precipitation during storms from 79 weather stations across Australia, spanning a broad range of climate zones, and compared them with near-surface temperatures. They found that the storms occurring at warmer temperatures had more uneven distributions of precipitation across the duration of the storm event, with lower rainfall at the beginning and end of the storm, and a more intense peak of precipitation. This pattern of rainfall extremes held across all latitudes - ranging from tropical to arid to cooler climates. Based on their statistical analysis in combination with hydrologic flow routing relationships, the authors estimate that for a 5 °C temperature increase, flood peaks could increase by 5 to 20 % in the Australian climate zones they studied.