New research has revealed that we don’t take climate change into account when considering current and future extreme rainfall.
Key points:
- Study finds methods for calculating likely maximum rainfall should be updated to account for climate change
- It finds that PMP estimates are expected to increase between 13 and 33% on average across Australia by 2100
- Dew point increases were highest in the South East and Tasmania
Probable Maximum Precipitation (PMP) is theoretically the highest possible precipitation at a given location.
It is essential in the calculation of the probable maximum flood (CMP).
These may be theoretical flood calculations, but they are fundamental to ensuring that our dams and other infrastructure are built to withstand the worst thrown at them.
So if the PMP and therefore the PMF are too low, the worst-case scenario is underestimated.
“While this is an extremely low risk, the consequences of this event are so dire that we need to take it into account,” said Johan Visser, PhD student at the University of New South Wales and lead author. of the article on the impact of climate change. on the operational estimates of the PMP.
Despite the high stakes, Visser said guidelines on how to calculate PMP are updated “rarely”.
“Australian guidelines for estimating PMP have not been updated since the late 1990s and early 2000s,” he said.
“That’s why we have a period of about 20 years of unaccounted climate data that hasn’t made it into the guidelines.
“So our question was, are these PMPs and the way they were calculated in the past still relevant if we know that atmospheric humidity has increased?”
Rising dew point
To see if atmospheric humidity has really increased, Visser and his colleagues looked at the dew point record.
The dew point is a measurement of atmospheric humidity, taken regularly at weather stations across the country.
“We are able to track what this dew point measurement has been doing over time and we can see that there are clear upward trends in atmospheric humidity over time,” said he declared.
For those going into detail, the maximum persistent dew point is used for the PMP calculations.
“So we see that dew point rising,” Visser said.
“That means atmospheric humidity is increasing. That means storms can be maximized to a higher degree.”
Not only has the dew point increased, but it is also expected to continue to increase.
“This shows that for all future climate scenarios that have been considered – from the highest emissions scenarios to the most conservative low emissions scenarios – all point to further increases in this maximum persistent dew point and therefore PMP up to at 2100,” Visser said.
“That’s what’s concerning.”
But dew point increases are not the same everywhere.
Visser and his colleagues found that dew point increases were highest in the southeast and in Tasmania, where many of the country’s large dams are located.
They found that PMP estimates are projected to increase by 13-33% on average across Australia by 2100.
PMP estimates on 546 large dams across Australia are expected to increase between 14.5 and 38% on average.
What should we do about it?
Mr. Visser stresses that these results do not constitute a call for an immediate modernization of all dams.
“It’s really hard to give a general recommendation or a site-specific recommendation,” he said.
“It really has to come down to an individual reassessment of the safety aspect of this failure mechanism.”
Rather, it calls for a change in methodology that incorporates new climate data and future climate projections.
“Renovating any dam would be an extremely expensive exercise,” he said.
“This problem is a symptom of a larger problem that we are already seeing.
“If you’re going to spend money on anything, reducing carbon emissions would be a good start.”
Fiona Johnson, a UNSW hydrologist who is not linked to the study, says this type of research is fundamentally needed.
“It’s great to see the industry help fund this kind of work,” she said.
“It has such strong applications to how the water industry as a whole thinks about the risk of these really serious events.
“Flood risk management is, in its most basic form, about making sure we know where the water will be so we can protect people and infrastructure from hazards as much as possible.”
Dr Johnson says there is always a trade-off and it’s not quite black and white.
“But it’s that if you don’t even understand the risk, you can’t even make those trade-offs,” she said.
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