Tropical Cyclone Alfred hit 600 kilometres of south-east Queensland and north-eastern New South Wales for a week with waves, wind and, especially, rain. It then transformed into an inland low-pressure weather system.
The week’s rain topped out at more than a metre at Upper Springbrook, in the Gold Coast hinterland, while 893 millimetres came down on Alfred’s outskirts at Dorrigo, NSW.
Fortunately, despite persistent rain mainly to Alfred’s south, the rain gauge at Lismore maxed out at just over 200 mm. South-east Queensland, however, experienced intense rains after Alfred crossed the coast on March 8.
The next day Hervey Bay, to the north, had its heaviest day’s rain in 70 years, as a thunderstorm started off a fall of more than 300mm.
Through that day and night, falls also reached up to 433mm at sites around Magan-djin/Brisbane. At 275mm it was Magan-djin’s wettest day since January 1974, in the wake of Tropical Cyclone Wanda.
Ex-Tropical Cyclone Alfred has turned out to be the latest “rain bomb”, rolling off fossil-fuel addicted capitalism’s production line of weather disasters.
More than enough rain bombs have come out of the Coral Sea in the last decade and a half. They caused flooding in Magan-djin in 2011, Bundaberg in 2013, and a metre of rain was dumped on Gurrumbilbarra/Townsville in 2019, with the flooding centred on Lismore, but it also spread from Gadigal Country/Sydney to north of Magan-djin in 2022.
Inevitably, these will happen again.
This is for four reasons, all of which are related to climate change.
First, surface sea temperatures have risen and are rising, which feeds energy into cyclones.
Second, air temperatures have risen and are rising, which allows more water vapour in the atmosphere, to fall as rain.
Third, air current circulation has weakened, at least in the tropics, so weather systems are moving more slowly.
Fourth, sea levels are rising which means storms surges start at a higher level than otherwise.
Cyclone heads south
Alfred formed in the northern Coral Sea and then moved south. It then turned west, moving slowly towards south-east Queensland's coast, initially as a category 2 cyclone (the category rates its wind strength between 1 and 5 above “normal” low pressure systems).
An ocean swell and massive winds pounded the coast. Waves gouged sand away from beaches, leaving drops of up to six metres.
As Alfred approached the coast, its winds weakened, but still caused some building damage. With the ground also rain-sodden, tree falls contributed to power cuts to about 450,000 properties.
The quantity of rain swelled because Alfred, at times, was hardly moving. Rain combined with high tides, pushing water up the estuarine Brisbane River and its creeks to flood surrounding low-lying areas.
Other places experienced flash flooding. People reported sandbags, put in place to protect buildings, had been flung aside by the water currents.
One person died as a result of Alfred’s weather, with others injured. River flooding added to the damage caused to landscapes and property.
Alfred unusual?
Many commentators have said Alfred is unusual, because it is the first cyclone in half a century to come this far south and make landfall, rather than dissipating at sea or hitting New Zealand as storms.
But many previous southern rain bombs such as Magan-djin’s 2011 flood, Bundaberg in 2013 and New Zealand in 2023 sprang from cyclones. These cyclones were different to Alfred because they had already degraded to low-pressure systems as they left the tropics.
Furthermore, between 1883–97, 24 severe cyclones and ex-cyclones reached at least south-east Queensland, as did others in the 1950s and 1960s.
After 1976, more El Niño conditions, drying eastern Australia through ocean current changes, contributed to reduced cyclone activity south of the tropics. No relationship between El Niño and climate change has been established, which means more La Niña — El Niño’s reverse — and neutral conditions, like now, are possible. That will enable a renewal of frequent southward-reaching cyclones.
That does not mean more frequent cyclones and that is not the trend.
Heat, wind, water
However, with surface sea temperature rises across normal seasonal variability, higher evaporation forces more heat and moisture into the atmosphere, including where cyclones form when the sea temperature exceeds 26.5°C.
Thus, of the cyclones that do occur, a higher proportion will be more intense in their wind strength, a trend already supported by evidence from the northern hemisphere.
Cyclones are also reaching their maximum intensity in areas further south in the southern hemisphere and closer to coasts. At the same time, warmer air can hold more moisture, leading to more intense rain.
Generally, this appears as a rise in rainfall intensity of about 7% for every °C of warming. But, in thunderstorms and cyclone eye walls, and feeder bands, this rate may double or triple.
These windier, wetter and more damaging cyclones and low-pressure systems are moving more slowly than before, so that, on average, each creates more rain in an area. In the tropics, wind speeds have fallen 5–15%.
The winds that steered Alfred westward, once it hit a high-pressure region to its south, were not very strong. That could be replicated in the future.
Storm surge — the body of seawater pushed ahead of a cyclone that spills over land, is historically 5–10 m above sea level. As baseline sea levels rise, storm surges can reach further inland.
Communities in Magan-djin and northern NSW prepared for Alfred’s landfall as best we could: stocking up supplies, sandbagging, preparing to evacuate, readying for rescue work and putting in place repair personnel and resources.
But all such action comes at a cost — physical, mental, environmental and economic.
In other words, inaction on greenhouse gas emissions creates this cost. If governments only respond to the impacts of climate change, those costs will grow at an accelerating rate.
In a climate-challenged world, rain bombs are expected to be bigger and faster. Society faces the urgent question of what governments will do now, as evidence of the devastating impact of catastrophic climate change is well known.
Will governments continue on with their business-as-usual drive for profit to expand already accumulated capital?
The system is changing the climate; change the system and we can change what the climate will otherwise become.
[Jonathan Strauss is standing for Socialist Alliance in the Queensland Senate. He acknowledges using material from the Conversation and thanks Professors Jon Nott and Steve Turton for providing advice.]