Are tropical storms in Australia getting stronger?

Floods, bushfires and earthquakes are all consequences of climate change. These have been affecting animals and their habitats for a long time. For some years now, the consequences have also been affecting people and their homes. Should Australia expect more and stronger cyclones?

Recently, there have been a lot of cyclones in Australia. Looking at the data from the Bureau of Meteorology over the last 110 years provides a surprising insight. What will happen with tropical storms because of climate change?

Cyclone Alfred hit southeast Queensland at the end of February, causing a lot of damage. Tropical storms usually cause problems like flooding, heavy rain, storm surges, hail and wind. This can lead to property damage and, in the worst-case scenario, even cost lives.

Tropical storms usually happen from November to April. Scientists agree that environmental disasters like droughts and floods are made worse by climate change. The question arises as to how climate change will affect cyclones.

Where do cyclones rage most frequently?

The terms ‘hurricane’ and ‘typhoon’ are often used as synonyms for tropical storms. The only difference is the names given to tropical cyclones in different regions. Hurricane is used in the North Atlantic, the central North Pacific and the eastern North Pacific. While in the Northwest Pacific, cyclones are called typhoons. Not all parts of Australia are equally affected by cyclones.

The north-west coast between Broome and Exmouth is considered a particularly cyclone-prone area. Most tropical cyclones are recorded at these locations. A high number of cyclones also occur in northern Queensland, where Cyclone Alfred was recorded.

The Bureau of Meteorology provides regular updates on cyclones. However, not every cyclone has a name. Many are only recognised and recorded as cyclones afterwards.

What the Cyclon Alfred caused

Tropical Cyclone Alfred was particularly felt in south-east Queensland. It was followed by strong winds, widespread power outages, heavy rainfall and associated flooding. It also ultimately led to severe coastal erosion on the beaches.

The Bureau of Meteorology reports three to five-meter high waves along the Sunshine Coast. It is also estimated that millions of cubic metres of sand were swept from the beaches. From Brisbane to the north-eastern coast of New South Wales, five to eight metre high waves were observed.

The largest waves were recorded in Tweed Heads Offshore with a height of 15 metres. According to the Bureau of Meteorology report, over 500,000 customers lost power. Some were without power for several days. Cyclone Alfred was able to develop and intensify due to favourable conditions.

How do cyclones form?

For a cyclone to develop, there are certain conditions that must be met. Temperatures of at least 26 degrees are needed for tropical storms to develop.

In addition, the young cyclone must be at least 500 kilometres away from the equator in order to achieve the necessary rotational force. As soon as a tropical cyclone forms, it needs a constant supply of warm, moist air in order to persist. As the moist air rises, the water condenses and releases heat, warming the air further. This causes the air to rise faster and the cyclone becomes stronger. But how has the number of cyclones in Australia changed over the decades?

There have been far fewer cyclones in recent decades than there used to be. Australia is also struggling with climate change. According to reports from the New South West Government, every decade since 1950 has been warmer in Australia than the decade before. This is reflected in the warmer daytime and night-time temperatures.

Australia’s warmest year was in 2019, when temperatures went up 1.52 degrees above the average at that time. A similar trend is reflected in the temperature of the oceans. The oceans have warmed by around one degree since 1910. Another way to measure this is to look at how long cyclones last.

The length of hurricanes has flattened out in recent years. Cyclone Alfred lasted a relatively long 17 days. It formed around 21 February and its direct effects lasted until 9 March. This was longer than the average for any of the decades that have been recorded. But the decade that has just begun is still the shortest on record.

In the last five years, the faster cyclones have decreased, while the weaker ones have experienced a small upswing. Scientists divide cyclones into five storm categories.

• Category 1: Up to 125 km per hour
• Category 2: 125 to 164 km per hour
• Category 3: 165 to 224 km per hour
• Category 4: 225 to 280 km per hour
• Category 5: Over 280 km per hour

While only minor destruction is caused in the lower categories, hurricanes in the higher categories cause large-scale power outages and major property damage. The categories of cyclone can be different depending on the location. For example, a category three cyclone can become a category two as it approaches land, and vice versa.

Alfred started out as a category one cyclone and was upgraded to category four in the meantime. When it reached the coast of Brisbane, it was only a category one until it lost its remaining energy there.

A tropical cyclone loses energy as it moves over land or cooler oceans. Otherwise, they are made weaker by unfavourable atmospheric conditions, such as dry air.

How La Niña affects cyclones

La Niña is the strongest influence on annual climate variability in most parts of the country. On the one hand, La Niña leads to more rainfall in parts of Australia. Daytime temperatures are cooler in the southern tropics and nighttime temperatures are warmer in the north. This is a shift in temperature extremes with a reduced risk of frost.

La Niña leads to more tropical cyclones. La Niña occurs when winds become stronger at the equator. This changes ocean currents, bringing cooler water up from the depths of the ocean. As a result, the water in the central and eastern parts of the tropical Pacific becomes colder.

At the same time, warm water is trapped in the western Pacific and north of Australia. The warming of the ocean temperatures in the western Pacific means that the area becomes more favourable for rising air, cloud formation and precipitation. As a result, heavy rainfall can occur north of Australia.