We used machine learning techniques to identify the climate drivers causing more thunderstorm downbursts. Increased heat and moisture over eastern Australia turned out to be the key ingredients.
The findings suggest air safety authorities and airlines in eastern Australia must be more vigilant during takeoff and landing in a warming world.
Warm, moist air spells trouble for planes
Global warming increases the amount of water vapour in the lower atmosphere. That’s because 1C of warming allows the atmosphere to hold 7% more water vapour.
The extra moisture typically comes from adjacent warmer seas. It evaporates from the surface of the ocean and feeds clouds.
Increased heat and water vapour fuels stronger thunderstorms. So climate change is expected to increase thunderstorm activity over eastern Australia.
For aircraft, the main problem with thunderstorms is the risk of hazardous, rapid changes in wind strength and direction at low levels.
Small yet powerful
Small downbursts, several kilometres wide, are especially dangerous. These “microbursts” can cause abrupt changes in wind gust speed and direction, creating turbulence that suddenly moves the plane in all directions, both horizontally and vertically.
Microburst wind gusts can be extremely strong. Brisbane Airport recorded a microburst wind gust at 157km/h in November 2016. Three planes on the tarmac were extensively damaged.
On descent or ascent, aircraft encountering microbursts can experience sudden, unexpected losses or gains in altitude. This has caused numerous aircraft accidents in the past. Microbursts will become increasingly problematic in a warming climate.
Microburst analysis and prediction
Microbursts are very difficult to predict, because they are so small. So we used machine learning to identify the environmental factors most conducive to the formation of microbursts and associated severe wind gusts.
We accessed observational data from the Bureau of Meteorology’s extensive archives. Then we applied eight different machine learning techniques to find the one that worked best.
Machine learning is a field of study in artificial intelligence using algorithms and statistical models to enable computers to learn from data without explicit programming. It enables systems to identify patterns, make predictions and improve performance over time as they take in more information.
We found atmospheric conditions in eastern Australia are increasingly favouring the development of stronger, more frequent thunderstorm microbursts.
We investigated a microburst outbreak from a storm front in 2018. It produced severe surface wind gusts at six regional airports in New South Wales: Bourke, Walgett, Coonamble, Moree, Narrabri and Gunnedah.
Regional airports in Australia and around the world often use small aircraft. Small planes with four-50 passenger seats are more vulnerable to the strong, even extreme, wind gusts spawned by thunderstorm microbursts.
Widespread consequences
Our extensive regional case study identified the weather patterns that create severe thunderstorms in eastern Australia during the warmer months.
High cloud water content creates a downward force in the cloud. This force induces a descending air current. When the heavier air reaches the ground, wind gusts spray out in multiple directions.
These wind gusts endanger aircraft during takeoff and landing, because rapid wind shifts from tail winds to head winds can cause the aircraft to dangerously gain or lose altitude.
Our analysis highlights the elevated aviation risks of increased atmospheric turbulence from thunderstorm microbursts across eastern Australia.
Smaller aircraft at inland regional airports in southeastern Australia are especially vulnerable. But these sudden microburst-generated wind gusts will require monitoring by major east coast airports, such as Sydney and Brisbane.
Beware of heightened microburst activity
Flying has long been recognised as a very safe mode of travel, with an accident rate of just 1.13 per million flights.
However, passenger numbers worldwide have increased dramatically, implying even a small risk increase could affect a large number of travellers.
Previous research into climate-related risks to air travel has tended to focus on high-altitude cruising dangers, such as clear air turbulence and jet stream instability. In contrast, there has been less emphasis on dangers during low-level ascent and descent.
Our research is among the first to detail the heightened climate risk to airlines from thunderstorm microbursts, especially during takeoff and landing. Airlines and air safety authorities should anticipate more strong microbursts. More frequent wind gust turbulence from microbursts is to be expected over eastern Australia, in our ongoing warming climate.
