Climate scientists discuss floods and future risk

The deluge that swept through southeast Queensland and northern New South Wales over the past week was devastating. Floodwaters peaked at around 14.4 metres high in Lismore – two metres higher than the city’s previous record.

So how does this compare to Australia’s previous floods, such as in 2011? Is it possible to expect more floods on this scale with climate change? The answers to questions like these aren’t straightforward.

Climate change doesn’t tell the whole story, as extreme rainfall can occur for a Many reasons. What’s more, it’s too soon to officially state whether this event is directly linked to climate change, as this would require a formal event attribution study. This can take several months or even years to complete.

We know that extreme events such as this will be more common in a warmer environment. This is one of the most severe natural disasters in colonial Australian History.

This is how it compares to floods in the past

Heavy rainfall and flooding are common along the east coast. The Yugarabul and Yugarabul communities have Traditional stories about great floods in the Brisbane river region long before European colonisation, and sediments from floodplains indicate floods as severe as those in 2010–2011 have occurred At least seven times in each of the last 1,000 years.

Instrumental records Documentary accounts show severe floods have inundated southern Queensland’s cities and towns in the 1820s, early 1840s and 1890s, 1931, 1974 and, of course, in 2010–2011.

Each of these events have been devastating, and record-breaking, depending on which records you’re interested in.

The floods of 1841 and 1893 are the highest in terms. Brisbane city records water levelsIt reached over 8m. Australia’s wettest day on record was also recorded in 1893, when Crohamhurst in the Glasshouse Mountains measured 907 millimetres in one day.

Continue reading:
IPCC report: Cities along the coast are beacons for climate change. It’s the place to be when we prepare ourselves for the inevitable.

The 1974 event was associated to extreme rainfall totals along many coast areas, including 314mm in Brisbane in one day and more than a metre rainfall over three days in places like Mount Tamborine or the northwest of Surfers Paradise.

The 2010–11 flood, while not as severe in terms of extreme rainfall totals, Its inland coverage was noteworthy., and was the final act of Australia’s wettest July to December on record.

The current flood has peaked at 3.85m in Brisbane, below the 2010–2011 levels of 4.46m. But it’s breaking records in other areas such as Lismore in northern NSW. This event is also causing the rainfall statistics to be near the highest ever recorded for many areas, possibly due the slow-moving nature the associated weather system.

Four of the six highest rainfall totals in NSW are recorded here Recorded on February 28,Brisbane just experienced three days with over 200mm. These aren’t the highest daily totals ever recorded in the city, but the first time three days of such intense falls have been documented, in data that go back to 1841.

Climate change: How to disentangle the role

When it comes to understanding the role of human-induced climate change in extreme events, there is the temptation to ask the wrong question: “did climate change cause this event?”

Since any extreme event is always a manifestation of climate variability, large weather systems, local-scale weather and climate change, it’s impossible to categorically answer this question with a simple “yes” or “no”.

Instead, the question we should be asking is “did climate change Contribute to this event?”

First of all, there has been a slight DiminutionSince the mid-20th Century, there has been a significant increase in summer rainfall in northeast NSW and southeast Queensland. But, there’s very high variability in rainfall for this region, and La Niña – a natural climate phenonenon associated with wetter weather – often brings flooding to this area, as we saw in 2010/2011 and in the 1970s.

Indeed, the effect of La Niña (and its counterpart El Niño, associated with drier weather) makes identifying a climate change-related trend more difficult. The natural high variability makes it difficult to identify a human-caused signal of climate change.

For every degree Celsius global warming, the atmosphere can retain approximately 7% less moisture. We also need the right weather systems to trigger the release and cause extreme rain. These systems are vulnerable to climate change.

Continue reading:
New IPCC report shows Australia is at risk from climate change. Future risks are high and Australia needs wide-ranging adaptation.

Climate change and weather system

The severity of the flooding in southeast Queensland is partly due to a weather system called an “Atmospheric river” sitting over the region for days. To make matters worse, the rain fell on an already sodden ground due to both the higher-than-average rainfall from the current La Niña, and the La Niña in the 2020-2021 summer. This made a big difference in the magnitude of the floods.

We don’t fully understand how the persistence of these natural systems will change in future, but recent work shows climate change will cause long-lasting atmospheric rivers over Sydney to occur It happens almost twice as oftenBy the end of this century. We don’t know yet if that’s also true further north of Sydney.

To complicate things further, there’s Do you have evidence? to suggest climate change may be influencing the frequency, intensity and impacts of El Niño and La Niña events.

Climate change projectionsAlso, it is possible that we will see small increases in the frequency of extreme one-day rain events, which can lead to flash flooding in eastern Australia. But there’s a lot of uncertainty.

And all over the world Monday’s report from the Intergovernmental Panel on Climate Change projected that global warming of 2℃ this century will bring twice as much flood damage compared to 1.5℃ warming. This jumps to 3.9 times more flood damage at 3℃ warming.

While the role of climate change is hard to pin down in Australia’s biggest floods, we know flooding often strikes our east coast. It would be beneficial to increase our resilience to severe flooding.

We can make ourselves less vulnerable to these types of events by taking steps like concentrating new housing or infrastructure projects in areas above floodplains.

Continue reading:
Climate change will make flooding more likely, just like rivers in a sky: floods to Queensland’s weather system.