Human-caused climate change will make strong tropical cyclones twice as frequent by 2050, putting large parts of the world at risk, says a new study published in Scientific Advances. In addition, Australia will see a significant relative increase in its population exposed to tropical cyclones.

Until now, predicting changes in the frequency and intensity of tropical cyclones was challenging — particularly at a local scale. This was hindering risk assessments and mitigation strategies. 

An international group of scientists, led by Dr Nadia Bloemendaal, set out to overcome this by using a novel methodology to map tropical cyclone risk. They obtained results at a global scale and with a high spatial resolution of just 10 kilometres. The analysis shows that climate change will cause more frequent and intense tropical cyclones over the coming decades. It also projects that maximum wind speeds associated with these cyclones could increase up to around 20 per cent.

Dr Bloemendaal, from the University of Amsterdam’s Institute for Environmental Studies, says the datasets are now publically available. This means governments and organisations can analyse tropical cyclone risk more accurately for every individual coastal city or region. This supports the development of risk mitigation strategies aimed to minimise impacts and loss of life. “Our results can help identify the locations prone to the largest increase in tropical cyclone risk. Local governments can then take measures to reduce risk in their region, so that damage and fatalities can be reduced”, said Dr Bloemendaal. 

Risk-assessing tropical cyclones

Tropical cycles are amongst the world’s most destructive extreme weather events. They cause the highest insured losses of any natural hazard, exceeding USD $480 billion in the United States alone last decade. But, they are currently relatively rare. Only around 80-100 tropical cyclones form globally in a given year, and most of these never make landfall. Furthermore, accurate global historical records are scarce and only span the last 30-100 years. This lack of data makes tropical cyclone modelling challenging, particularly at local levels.

The scientists used historical data combined with global climate models to generate hundreds of thousands of “synthetic tropical cyclones” to overcome this limitation. This allowed much more accurate predictions for the occurrence and behaviour of tropical cyclones over the next decades in the face of climate change. Researchers can use the dataset to model behaviours even in regions where tropical cyclones rarely currently occur, as well as model alternative climate scenarios and time periods. 

The analysis shows the frequency of the most intense cyclones – those from category three or higher – will increase globally due to climate change. The study also found that weaker tropical cyclones and tropical storms will become less common in most of the world’s regions, with the only exception being in the Bay of Bengal. 

The human impact

The study found that countries with relatively rare tropical cyclones will see an increased risk in the coming years. “Of particular concern is that the results of our study highlight that some regions that don’t currently experience tropical cyclones are likely to in the near future with climate change”, states Dr Ivan Haigh, Associate Professor at the University of Southampton.

These include Cambodia, Laos and Mozambique. Many Pacific Island nations, such as the Solomon Islands and Tonga, will also be affected. These small island developing states are typically characterised by high vulnerability to climate impacts. This is in addition to scarce financial resources and small economies to overcome such impacts. 

Asia will see the largest increase in people exposed to tropical cyclones. This is in terms of absolute impact on populations. Countries that will have millions more people exposed include China, Japan, South Korea and Vietnam. 

Tropical cyclone risk in Australia

The dataset suggests that Australia faces the largest relative increase in people exposed to category three tropical cyclones. This is within the group of countries with current return cyclone periods below 500 years.

The researchers applied the dataset to Cairns, Queensland to project the chance of an intense tropical cyclone. For category three or higher, the probability went from once every 48 years in the present to once every 21 years in the near future.

For the chance of a category five tropical cyclone in Cairns, the current return period is 2,500 years. The probability in the future increases substantially once every 330 years. This is over a sevenfold increase within the next few decades.

The study should be a wake-up call for governments. Leaders must prepare now to limit risks to life, property and ecosystems. This is in addition to robust climate mitigation actions, such as phasing out fossil fuels. Such measures are vital to ensure the very worst effects of climate change, such as these extreme weather events and disasters, are never felt.