Ground-breaking new study finds phenomenon cannot be explained by typical climate variability

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A groundbreaking new study (10.1126/science.abn8657) has found rapid rain bursts have intensified over Sydney by 40% in the last 2 decades.

The findings have major implications for the city’s preparedness for flash flooding and associated impacts in the future.

“Sydney has seen rapid rain bursts intensify at an alarming rate in the last two decades” says Dr Hooman Ayat from the ARC Centre of Excellence for Climate Extremes.

“Our study utilises a new technique to give us more information on these rapid rain bursts than was previously possible. Using weather radar data, we identified thousands of rapid rain bursts in Sydney over two decades and saw a 40% increase in intensity. What’s particularly concerning is that we weren’t able to identify usual climate variability as driving this change, so climate change may be a factor in this shocking result”

The study has major implications for Sydney and potentially cities all over the world.

Professor Steven Sherwood (L), Professor Jason Evans (R)

“If this trend continues in Sydney, the city needs to be more prepared for rapid rain bursts and flash flooding into the future” says Professor Jason Evans.

“This should factor into our city planning with buildings, roads and communities needing to prepare for the likelihood of more rapid rain bursts to test the short term capacity of our drainage, roads and flood plains” says Evans.

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The study uses a groundbreaking new technique that uses weather radar data, rather than rain gauges, satellite data and climate models, which to this point have struggled to accurately  identifying rainfall on such short timeframes.

Professor Steven Sherwood (L), Dr Hooman Ayat (R)

“We’ve been able to use this technique to gain insights into a possible extreme rain future for Sydney, but we think this technique can also help other cities assess recent trends and prepare for the future.” says Professor Steven Sherwood.

“If what we saw over Sydney is occurring in other cities around the world, governments, councils, city planners and communities need to prepare for the possibility that rapid rain bursts will get more and more extreme. This is a concerning new phenomenon that needs more research.”

The research is published today in the Science journal – 10.1126/science.abn8657

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Editor’s note:

What is a rapid rain burst?

A rapid rain burst is a short period of extreme rain occurring over a duration of about 10 minutes.

During a rapid rain burst, a huge amount of water falls rapidly over a small region, increasing the likelihood and severity of flash flooding, especially in urban and steep mountainous regions.

Extreme rain is defined by the area experiencing it. What’s considered extreme rain in one location might not be considered so in another. Rapid rain bursts are the most extreme 5% of rainfall in a location.

Prior to 2022, it was difficult for climate scientists to identify changes in rapid rain bursts due to limitations on rain gauges, satellite data and climate models in identifying/detecting these small-scale storms.

A new technique, developed by researchers at the ARC Centre of Excellence for Climate Extremes, identified thousands of rapid rain bursts over Sydney Australia using weather radar data over two decades.

Using this technique, they found that the most severe rapid rain bursts have intensified by 40%  over Sydney, Australia in the last two decades – a phenomenon not explained by regular climate processes.

Researchers also refer to rapid rain bursts as “sub-hourly heavy rainfall”.

About the ARC Centre of Excellence for Climate Extremes

The ARC Centre of Excellence for Climate Extremes reduces Australia’s economic, social and environmental vulnerability to climate extremes.

Funded by the Australian Research Council (ARC), it brings together five Australian universities and a suite of outstanding national and international Partner Organisations.

The participating universities are the University of New South Wales, Monash University, the Australian National University, the University of Melbourne, and the University of Tasmania.