Parts of Australia have experienced extreme rainfall leading to floods again this summer, putting the spotlight on climate science.
What we know about how climate change contributes to these extreme rainfall events and flood estimation now and in the future is the focus of an updated chapter in Australia’s Rainfall and Runoff Guidelines, now in its final stage of public consultation.
The national guideline document is one of the most widely used references to help engineers and the construction industry manage flood risk for the built environment. Consideration of climate change was included for the first time in Australia’s Rainfall and Runoff guidelines released in 2016.
The climate science initially used to inform the development of that advice is now a decade old.
The Department of Climate Change, Energy, the Environment and Water (DCCEEW), in partnership with Engineers Australia, started a project funded under the National Emergency Management Agency, Disaster Risk Reduction Package to update the Climate Change Considerations chapter.
A critical part of this work has been a comprehensive review of the latest science.
Led by University of Melbourne’s Dr Conrad Wasko, researchers from the Climate Systems Hub played an important part in that science review.
Dr Wasko said a particularly important element in the science review was work done extracting estimates of increases to rainfall intensity from journals to standardise these figures against global temperatures.
“It was a mammoth effort and it’s critical to the project’s success. We were pleased researchers received the funding to do that,” he said.
“This update is something the community needs and wants. Engineers want answers on how to deal with climate change and I get the feeling there can’t be enough guidance around it but it’s hard because there is a lot of uncertainty around climate change.
“There does now seem to be a reasonable consensus between different lines of evidence that rainfall is changing. Although there are large variations, we are at a point where our knowledge is converging, that gives us more confidence in what we’re doing and that’s a step change with the last decade.
“As the uncertainty around extreme events is reduced, there has been a shift in sentiment across industry and the public in terms of: This is no longer a future problem, it is a now problem.
“The language in the updated chapter is stronger and that will help those who want answers on how to plan.”
Dr Acacia Pepler is a research scientist with the Bureau of Meteorology and a member of the Climate Systems Hub team that worked on the science review and standardisation of data.
“The climate change chapter in the 2019 rainfall and runoff guidelines was based on the best available science at the time,” Dr Pepler said.
“What we’ve done now is a much more systematic review of what research has been done in the last decade, how much do we know, how extreme rainfall has changed and how it’s predicted to change in the future. We have come up with what we think is the best estimate of what the change in extreme rainfall is per degree of global warming. It has made it much clearer when it needs to be factored in.”
Climate Systems Hub scientists who also contributed to the review include, Dr Tim Raupach (UNSW), Professor Jason Evans (UNSW) and Dr Kathy McInnes (CSIRO).
The Update to the Climate Change Considerations chapter in Australian Rainfall and Runoff: A Guide to Flood Estimation (Discussion Paper) was released of consultation in December 2023 and feedback is now sought from engineers, peak industry bodies, governments and other subject matter experts on the draft chapter to ensure that the updated guidance will reflect user needs before the document is finalised in mid-2024.
To provide feedback on the proposed updates, go to the Department of Climate Change, Energy, the Environment and Water (DCCEEW) website.
Read more on the science behind the updated draft chapter:
Wasko, C., Westra, S., Nathan, R., Pepler, A., Raupach, T., Dowdy, A., Johnson, F., Ho, M., McInnes, K., Jakob, D., Evans, J., Villarini, G., and Fowler, H.: A systematic review of climate change science relevant to Australian design flood estimation, Hydrol. Earth Syst. Sci. Discuss. [preprint], https://doi.org/10.5194/hess-2023-232, in review, 2023.
See also our previous blog from Professor Jason Evans:
In the media:
It’s not just the total rainfall – why is eastern Australia experiencing such sudden, devastating downpours? The Guardian