New research undertaken by the Australian Research Council Centre for Excellence in Climate Extremes (CLEX) has discovered that short-duration, high intensity rainfall events have increased by 40% over the past 20 years in the Sydney region. This unprecedented rate of change has not yet been documented anywhere else in the world.
UNSW’s Professor Jason Evans and Professor Sherwood were two of the key researchers on the project, led by Dr Hooman Ayat a UNSW PhD student now at the University of Melbourne and joined by Joshua Soderholm from the Australian Bureau of Meteorology. The project, which recently featured in Science, analysed weather radar data from three overlapping radar stations at Newcastle, Terrey Hills and Wollongong on the New South Wales coast, looking specifically at rainfall events that were less than an hour in duration.
Professor Evans says that while the cause of the prominent increase is unclear, high rainfall intensity usually correlates directly with flash flooding, with implications across many communities and industries.
“Our discovery provides more evidence for communities and policymakers to prioritise adapting to an increasingly changing climate, with water infrastructure, transport and agriculture all in a vulnerable position,” says Evans.
“Existing stormwater systems and household water infrastructure in New South Wales are designed to standards that were developed using historical extreme rainfall data—so it’s important we keep collecting new information and adjusting these standards as needed.”
The Intergovernmental Panel on Climate Change (IPCC) recently stated that rainfall trends are not comprehensively understood due to a lack of data for studies on short duration rainfall—defined as rainfall events less than an hour in duration. Past studies have largely focused on changes in daily or longer duration rainfall extremes, used unreliable rainfall gauges with limited success, or relied on satellite data that is unable to adequately capture short duration heavy rainfall events.
The CLEX study used reliable ground-based weather radar provided by the Bureau of Meteorology, providing a relatively complete observation of these rain systems in space and time that overcame the limitations of conventional methods.
Prof Sherwood says that this method could be utilised in other areas to improve rainfall modelling and predictions.
“There are other regions and parts of the world where similar, overlapping radar data may be available for analysis,” says Sherwood.
“We are interested in discovering where in the world similarly high increases in rainfall intensity have been observed, and this may be something we investigate in future.”
The research suggests that the increase in short-duration, high-intensity rainfall events does not appear to be directly linked to known natural variability such as El Nino, but that potential links to climate change require further investigation.
The full paper, ‘Intensification of sub-hourly rainfall’ can be accessed online at Science.org—one of the world’s leading scientific journals.