Why does Australia get so many storms in summer?

Meteorologists forecast more storms and heavy rain to come over south-east, as western Sydney records more than 100,000 lightning strikes

Stormy weather has hit parts of Australia this week, driven by tropical moisture and low pressure troughs across the country.

On Tuesday, intense storms and heavy rain left thousands without power in Geelong and the Bellarine peninsula in Victoria, while lightning lit up the skies in New South Wales.

According to Weatherzone, about 133,000 lightning strikes were recorded within a 100km radius of Blacktown in western Sydney.

Lightning storm over the Sydney basin tonight. Seen from Bilpin in the Blue Mountains #SydneyStorm #Sydney #storm #StormHour #bluemountains #Weather #Lightning pic.twitter.com/BitS2bZLHj

— Greg Bourke (@GregBourke3) January 24, 2023

Ben Domensino, a Weatherzone meteorologist, has forecast that “Australia will see widespread and locally heavy rain over the course of this week.”

“The rainfall being predicted over eastern and south-eastern Australia this week will come from daily shower and thunderstorm activity,” he said in a statement.

Why are storms more common in summer?

Most storms occur between September and March, according to the Bureau of Meteorology. Thunderstorms require warm, humid air to form, and strike more commonly in the summer months when solar energy is abundant.

There are three key components required to produce a thunderstorm, according to the BoM:

  • High moisture in the atmosphere, which can sometimes be identified by the presence of low clouds or haziness in the morning.

  • An unstable atmosphere, with high temperatures near the ground that fall sharply with increasing height.

  • A trigger that lifts air up vertically in the atmosphere, through differences in air density. This can arise from local variations in heating, or the approach of a front or low pressure trough.

“High moisture levels, especially near the coast, affect the tropical north of Australia in the summer half of the year,” the BoM has previously noted. Conditions in the northern half of Australia between October through March were favourable for thunderstorms, it said. “Lower pressure lies across northern and central Australia, and gives rise to the vertical motion and low level convergence that favour thunderstorm development.”

But it also said “severe winter storms linked to cold fronts are common in the south-west of Western Australia and south-east South Australia.”

What effect does climate change have on thunderstorms?

According to the CSIRO’s 2022 state of the environment report, daily rainfall totals associated with storms have increased in Australia since 1979, especially in northern parts of the country. “This is primarily due to an increase in the intensity of rainfall per storm,” it found. In future decades, Australia is projected to experience fewer tropical cyclones, but an increased proportion of high-intensity storms with higher rainfall.

Rainfall events are predicted to intensify with global heating, as the atmosphere is able to hold about 7% more water vapour for each degree of warming.

Rapid storm-related extreme rainfall events may intensify at an even higher rate, according to the Earth Systems and Climate Change Hub, because “the additional moisture in the atmosphere may also cause more intense convection for thunderstorms”. Short duration rainfall intensity could increase by about 15% for each degree of warming, it has warned.

Historical analysis by the BoM found no consistent link between peaks and troughs in thunderstorm frequency and El Niño or La Niña events. However, it found “some evidence that thunderstorms tended to be less frequent over south-eastern Australia” – Sydney, Adelaide and Canberra particularly – during strong El Niño years.


Donna Lu Science reporter

The GuardianTramp

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