The recent tragic flash flooding in Texas claimed at least 135 lives and families are still sifting through debris where their homes once stood. Walls of water swept through towns with little warning. Could this happen in Australia and are we ready?
Thousands of Australians live in flash flood danger zones. Texas isn’t a far-off international tragedy; it’s a glimpse into a possible local future. These floods are an opportunity to reflect on the possibility of similar events in Australia and our preparedness to ensure communities are safe, resilient and sustainable.
Flash flooding can be caused by intense rainfall, particularly when it occurs over an area saturated by previous rain, leading to rapid stream rise. Steep slopes and narrow valleys can hasten water runoff and the likelihood of flash flooding. The Bureau of Meteorology (the Bureau) defines flash flooding as:
Flooding occurring within about six hours of rain, usually as the result of intense local rain and characterised by rapid rises in water-levels.
Flash flooding is particularly dangerous as it can be deep, fast flowing and occur with little to no warning. Initial stream rise can look like an inland tsunami, with people reliant on their own observations rather than formal warnings.
Previous Natural Hazards Research Australia (the Centre) research found at least 130 flash flood fatalities were recorded between 2000 and 2017 across New South Wales, Victoria, the Australian Capital Territory and southeast Queensland. Most of these deaths were a result of people attempting to cross a watercourse (Coates et al., 2017).
Many Australian communities are at risk of flash flooding, including densely populated regions including southeast Queensland, the Hunter Valley including Newcastle, the New South Wales Central Coast, Sydney including the Northern Beaches, Parramatta, Ryde and Fairfield, the Illawarra, Melbourne, Hobart and Adelaide.
Residents are not the only people at risk visitors and people travelling through areas prone to flash flooding are also in danger, including shoppers, campers, hikers and motorists.
Notable recent Australian flash floods include:
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Eugowra (2022): two fatalities and about 150 people airlifted from their roofs
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Hobart (2018): damage throughout the Hobart CBD
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Dungog (2015): three fatalities as flooding struck pre-dawn
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Toowoomba and Grantham (2011): devastation throughout the Lockyer Valley with 21 deaths
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Newcastle (2007): 10,000 to 15,000 homes affected with 1000 to 2000 experiencing over floor flooding and several fatalities.
The risk of flash flooding will only worsen in our increasingly warmer climate. As the warmer atmosphere can hold more water, increasing the frequency of intense rainfall. Urban development can also exacerbate flash flooding risk by increasing the coverage of impervious surfaces, meaning greater runoff during intense rain.
Flash flood warnings have the potential to save lives. Brown and Graham (1988) found that increasing flood warning delivery from a few minutes to 90 minutes reduced fatalities by more than 90 per cent.
In Australia, the Bureau provides broad scale warnings for heavy rain likely to cause flash flooding via Severe Thunderstorm Warnings and Severe Weather Warnings.
Flash flood warnings can be associated with high degrees of uncertainty. Flash floods are more difficult to predict than slower rising riverine floods. Centre research found that key terminology employed in Bureau flash flooding severe weather warnings is often misunderstood. Further research is finding communities often may not follow warning instructions, relying on local knowledge and information networks to make protective decisions for themselves and their loved ones.
The National Arrangements for Flood Forecasting and Warning state:
Responsibility for Flash Flood warnings and systems lies with the States and Territories in partnership with local government (where appropriate) within their jurisdictions. States and Territories generally determine localities at risk of Flash Flooding from flood studies as part of a formal risk assessment process.
Some local governments including Moreton Bay and Brisbane in Queensland and Newcastle and Parramatta in New South Wales developed local-specific warning services, while most other high-risk areas have no specific local warning services.
Methods to reduce flash flood risks include:
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Improve flash flood warning systems: Identify and fill warning system gaps for high-risk areas, including the provision of community engagement campaigns regarding flash flood risks.
The Centre is funding research with the Bureau on extreme rainfall and flood outlooks which will aid the ability to forecast conditions likely to result in flash flooding and has recently completed research on user needs for severe weather predictions.
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Treat flood risk to high-risk roads: Roads should be risk assessed as a standard component of floodplain risk management to identify priority road sites for improvement measures to maximise the safety of motorists during flash flooding. Centre research on the influence of road characteristics on flood fatalities provides some evidence to inform risk assessment methods.
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Invest in nature: Nature-based solutions should be evaluated as part of floodplain risk management planning. The Centre is currently funding research investigating the efficacy of nature-based solutions and recently completed a thought leadership paper with insurer Suncorp on nature-based disaster risk reduction solutions, highlighting the co-benefits of investing in nature.
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Land-use planning: Sensitive land-uses for example schools, childcare centres, hospitals and nursing homes, should be avoided in areas prone to flash flooding where there is no ability to safely evacuate in advance. Caravan parks where residents are at high risk should also be avoided, as demonstrated during flash flooding in Coffs Harbour in 1996, where a fatality occurred in a caravan park.
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Assisted relocation: In the highest risk areas where there is a significant risk to life assisted relocation programs should be considered to remove vulnerable structures from the floodplain.