Changes in hourly extreme precipitation in victoria, Australia, from the observational record

Abstract This study was driven by a need to inform how extreme precipitation might change in the future by considering guidance based on how it has already changed. Hourly precipitation data from eight high quality precipitation gauges from 1958 to 2014 in Victoria (Australia) were used. Variations in the magnitude and frequency of extreme precipitation events as well as their proportion of total precipitation were examined. On average, we found an 89% increase in hourly precipitation events exceeding 18 mm/h in the latter half of the study period as compared to the earlier half. The most extreme precipitation events increased in intensity by more than more moderate extremes, with larger increases during the warm season. The proportion of precipitation that could be attributed to extreme precipitation events during the warm season has increased in recent decades while annual precipitation totals have been declining. Extreme value modeling was performed to estimate how the 2, 10 and 100 year precipitation events have changed. A statistically significant increase could only be claimed for two sites for the 2 year return period precipitation event. However, the mean estimates of the 100 year return period precipitation events at five of the eight stations from 1987 to 2014 exceeded the 90% confidence intervals of the 100 year return period precipitation events from 1958 to 1985, while little change was observed at the other three sites. Our findings have implications for improved planning and resilience around intense rainfall and associated hazards such as flash flooding in Australia.