Floods are part of Australia's natural ecology. They are important for some ecosystems and for boosting dam inflows, but they can cause significant damage to property and infrastructure, physical and mental health impacts, and loss of life. Climate change will result in more severe flooding.
Floods are the most costly natural disasters in Australia, averaging $8.8 billion per year [pdf · 37.5mb] (as of 2017) for insured, tangible and intangible costs. Flood impacts are affected by the rainfall (intensity, frequency and duration), catchment characteristics, and the exposure and vulnerability of ecosystems and societies.
The extreme rainfall experienced in southeast Queensland and New South Wales in February-March 2022 was associated with a slow-moving weather system that formed after consecutive La Niña events in 2020-21 and 2021-22.
La Niña events typically bring wetter conditions to northern and eastern Australia, while El Niño events typically bring drier conditions to this area. This is due to natural variations in sea surface temperatures and weather patterns across the Pacific Ocean, commonly referred to as the El Niño – Southern Oscillation or ENSO. For more information regarding La Niña events, see What is La Niña and how does it impact Australia?
The specific contribution of climate change to such individual events is difficult to assess
We know that the Earth has warmed by 1.09 °C since 1850-1900, mostly due to human activities that have increased greenhouse gases. Warmer oceans and higher sea surface temperatures tend to increase the amount of moisture that gets transported from the ocean to the atmosphere. A warmer atmosphere can hold more moisture and can increase the intensity of extreme rainfall events. Hourly extreme rainfall intensities increased by 10–20 per cent in many Australian locations between 1966–1989 and 1990–2013. Daily rainfall associated with thunderstorms increased 13-24 per cent from 1979 to 2016, particularly in northern Australia.
Understanding the extent to which climate change has contributed to individual extreme events is less clear. This is because climate change is superimposed upon large natural climate variability.
Assessing the extent to which climate change and natural climate variability play a role in extreme events can now be done using climate models. This is otherwise known as “event attribution”. Various Australian attribution studies have been published for extreme temperature events, extreme rainfall events and extreme fire events . An event attribution analysis for the February-March 2022 flood event has not yet been performed.
It is expected that long-term climate change will result in greater climate variability with more intense extreme events than in the past
CSIRO research shows that Australia is likely to become warmer over the coming decades, with a reduction in average annual rainfall in the south and east. In contrast, average annual rainfall projections for northern Australia are uncertain.
As the climate warms, heavy rainfall events are expected to continue to become more intense. For example, the intensity of daily rainfall with a one-in-20 year average recurrence may increase 4-10 per cent by 2050 for a low emission scenario and 8-20 per cent by 2050 for a high emission scenario.
CSIRO research has shown a direct relationship between increasing greenhouse gas concentrations in the atmosphere and an increase in strong El Nino and La Nina events.
Some parts of Australia will be more vulnerable to flood risk
According to the Intergovernmental Panel on Climate Change (IPCC), the projected increase in heavy rainfall will increase flood risk in cities, built-up urban areas, and small catchments, where extreme rainfall over hours to a day can quickly become flash floods. It's more complex in rural areas and for larger river basins, where floods are driven by multi-day rainfall events and by the preceding soil moisture conditions.
More needs to be done to improve our resilience to floods
The federal government has a National Climate Resilience and Adaptation Strategy, and all States and Territories have climate adaptation plans, while most local councils have climate adaptation plans, and the private sector is developing climate risk and disclosure regimes. The 2019-2020 fires and 2022 floods in Australia highlight that regional vulnerabilities remain large.
The IPCC Working Group 2 report found that adaptation progress is ‘uneven’. Barriers to adaptation include lack of consistent policy direction, competing objectives, different risk perceptions and values, knowledge constraints, inconsistent information, fear of litigation, up-front costs, and lack of engagement, trust and resources.
The good news is that a range of incremental and transformative adaptation options and pathways is available. Key enablers include shifting from reactive to anticipatory planning, integration and coordination across levels of government and sectors, inclusive and collaborative institutional arangements, government leadership, policy alignment, nationally consistent and accessible information, decision-support tools, along with adaptation funding and finance.
Local ‘adaptation champions’ and tailored engagement processes can enhance learning. Knowledge brokers, information portals and alliances can help communities, governments and businesses to better access and use climate change information.
Recent initiatives like the Australian Climate Service and the National Recovery and Resilience Agency are positive steps to helping address risks from floods, fires, droughts, heatwaves and other hazards.