Unprecedented rain brought by has triggered widespread flooding in far north Queensland, forcing thousands of people to evacuate. Cairns airport is , roads are extensively damaged and residents in the city’s northern beaches are cut off by floodwaters.
Author
Steve Turton
Adjunct Professor of Environmental Geography, CQUniversity Australia
Some rain gauges in the Barron and Daintree River catchments recorded over recent days, and . Water levels in the lower Barron River have set by devastating floods in . On Monday morning, the Daintree River was higher than the previous 118-year-old flood level, recorded in 2019.
The full impacts of the flood are not yet clear. But there’s likely to be significant damage to properties and public infrastructure, and negative effects for industries such as tourism and agriculture. Recovery is likely to take many months.
So let’s take a closer look at what caused this emergency – and what to expect as climate change worsens.
A ‘sweet spot’ for torrential rain
Tropical Cyclone Jasper t north of Cairns on Wednesday last week, tracking over the remote Indigenous community of Wujal Wujal. Damage from wind and storm surge was minimal, but Jasper still produced more than 800mm of rain across the Daintree and Mossman River catchments.
Late Wednesday, the cyclone was downgraded to a tropical low. It crossed southern Cape York Peninsula and headed towards the Gulf of Carpentaria. By Friday, local tourism agencies and operators they were back in business, inviting visitors back to the region.
However, by Saturday morning, a significant rainfall and flood emergency was unfolding across a 360 kilometre swathe from Cooktown to Ingham. So what happened?
The ex-cyclone stalled just inland from the southeast Gulf of Carpentaria, creating a sweet spot for torrential rain known as a “stationary convergence zone”. Incredibly moist tropical winds collided over a narrow zone between Port Douglas and Innisfail. This effect converged with northerly winds from the Gulf of Carpentaria and southeast trade winds from the Coral Sea. Local mountain ranges created extra uplift. All this led to non-stop torrential rain for 48 hours.
As a result, an emergency situation rapidly grew across Cairns and the Barron River delta to its immediate north.
Townsville floods: similar but different
This extreme flood event bears some similarity to that which caused in February 2019. Both were associated with a stationary convergence zone caused by a stalled tropical low located to their northwest. In the case of Townsville, the tropical low did not budge for more than ten days. In that time, Townsville received the equivalent of a year’s average rainfall.
Otherwise, the two events are very different.
Firstly, the Townsville floods occurred during a – that is, in the absence of the climate drivers La Niña and El Niño. But the current flood event has occurred during an , when tropical cyclones are much less likely to , especially in early December.
Secondly, the deep tropical low that caused the 2019 Townsville floods was embedded in an , which sucked in . But unusually, Cyclone Jasper did not form in such conditions. The monsoon trough is still to appear and form over northern Australia.
What’s climate change got to do with it?
As 2023 closes as the , there is growing global concern about the rise of such as floods, droughts and heatwaves.
The atmosphere and oceans are warming due to increasing emissions of , largely caused by burning fossil fuels. This has led to a greater risk of extreme rainfall and flooding, such as the events we’re seeing now in far north Queensland.
For every 1°C rise in average global temperature, the atmosphere can hold . When the right atmospheric “triggers” are in place, this extra water vapour is released as intense rainfall.
It’s too soon to attribute the current extreme rain and flooding to climate change. But as the world continues to warm, such events will become more frequent and severe.
Already, extreme flood events globally are becoming and their magnitude is many long-term rainfall and river flood records.
Looking ahead
Once the immediate crisis in North Queensland has subsided, local and state authorities will need to grapple with how to deal with the “new normal” of extreme weather events. The big question is: are they prepared?
Since the big , considerable residential and commercial development has been permitted across the river’s floodplain. In many cases, these earlier developments were approved without full consideration of . Many were also approved before local government planning started taking sea level rise into consideration.
The wider Cairns community will recover from this extreme event and will hopefully take on board any problems identified in the emergency responses. In future, emergency planning must take the effects of climate change more seriously. This includes increases in sea level, and more intense tropical cyclones, storm surges, rainfall and flooding.
As of this month, a climate emergency had been declared in around the world. As a result, many jurisdictions have developed response plans. In Australia, local governments should recognise climate change threats and risks by formally declaring a climate emergency.
Steve Turton has previously received funding from the Australian government.
