It’s astounding what can be achieved in 30 years of climate science.
In 1987, the potential impact of global warming was just becoming front page news and CSIRO launched its inaugural Greenhouse conference, which has grown to become an internationally recognised forum for the latest in Southern Hemisphere climate research.
In the same year, Engineers Australia released an update of the Australian Rainfall and Runoff (ARR) guidelines, which included predictions of changes in atmospheric circulation due to a build-up of carbon dioxide.
More than three decades later, the ARR has been updated and draws on sophisticated climate modelling that was unthinkable in the 1980s.
The update, first released in draught form in 2016, marks a significant leap forward for the ARR. With the exception of minor amendments in the 1990s, little of the ARR had changed and engineers have been relying on the same set of guidelines since global warming awareness first hit the mainstream.
Designed to assist in the assessment flood risk when developing new infrastructure, the updated ARR reflects significant technological advances in rainfall and runoff assessment and includes guidance and datasets to produce accurate and consistent flood studies and mapping.
Three decades in the making
Delivered by Geoscience Australia, in collaboration with Engineers Australia, the update features an additional 30 years of data collected from across the country, including observations from more than 10,000 rainfall gauges and 100,000 storm events.
“We’ve used pretty much every rain gauge in Australia to understand the probability of rain fall and to understand how storms occur in space and time,” explained Mark Babister, Managing Director at WMA Water and co-editor of ARR.
“We have some pretty fancy computer modelling techniques now for modelling floods in terms of rainfall into runoff and runoff into flood levels.”
While technology has played a vital role in providing accurate updates, the project was delivered thanks to a large team of volunteers, most of whom are member of Engineers Australia.
“Two thirds of the effort was from unpaid by volunteers,” said Babister.
“We received $9.15 million worth of federal funding and the Bureau [of Meteorology] spent about $4 million looking at the rainfall. We received huge amounts of in-kind contributions.”
Accounting for climate change
Previous editions of ARR were paper-based documents; however, the current edition makes full use of modern electronic data delivery.
All maps have been converted with a simple, searchable geo-spatial interface to enhance usability, and text sections are available in various electronic formats.
The 2019 update includes the addition of Book 9, which explores the complexities of urban development. However, Babister said much of the update addresses climate change.
“It was mentioned as a potential issue in the 1987 update, but now we have put in some adjustments of how extreme rainfalls are going to change in the future,” he said.
“To be honest, the issues of extreme rainfalls are really complex. It starts off very simple — as the world starts to warm up, you can hold more moisture in the atmosphere, so our extreme storms can become heavier. After that, you go to the next level of complexity.
“We’ve put in some broad-brush factors that people use during design,” he added.
“For example, if you’re planning for a subdivision, you can look up what the implications are in 2090. However, there is still a fair bit of uncertainty about that, as we don’t know how much CO2 we’re going to produce or who we’re going to elect in Australia or the world.”
Babister explained the latest ARR guidelines use the Representative Concentration Pathway, which is a greenhouse gas concentration trajectory adopted by the Intergovernmental Panel on Climate Change (IPCC). There are four pathways selected for climate modelling and research, all of which depend on future levels of greenhouse gas emissions.
“For example, a 100-year, one-hour storm will probably go up by about 20 per cent by 2090 under a high-carbon-emission scenario,” says Babister. “That means that if your house is set at the 100-year flood level, it’s probably going to end up at the 50-year flood level and you will have water through your house twice as often and your street will overflow twice or three times as often.”
Avoiding risk
Babister said the cheapest and most effective way to deal with flooding is to avoid unacceptable risks.
“Most of the solutions are actually quite local,” he said.
“Often, we might put in a process to encourage people to raise houses because flood insurance is quite a fickle thing. There’s also some good information in Book 6 on hydraulics, which includes diagrams of people in cars and when they get swept away. We are mapping that all round Australia and trying not to put people and cars at risk.
“That kind of mapping is used all the time for where to put suitable infrastructure. It stops people building childcare centres and schools and nursing home facilities in high-risk areas.”
Babister said the 2019 ARR update represents 30 years of advances in technology and scientific understanding of rainfall, runoff and flood producing processes.
“While we’ve invented computers for everyday use, we’ve been stuck in the dark ages until recently,” he said.
“It’s a bit of a quantum leap as technology has changed so much. The ARR update was still a mammoth task and it took so long to convince government and others to fund it. They sort of thought we could all do it in our spare time.”
