What are atmospheric rivers? – Australian Geography
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Dr. Karl Kruszelnicki
Donor
Dr. Karl Kruszelnicki
Dr Karl is a prolific broadcaster, author and Julius Sumner Miller Fellow at the University of Sydney School of Physics. His latest book, Vital Science is published by Pan MacMillan. Follow him on Twitter at @DoctorKarl
By Dr Karl Kruszelnicki
October 10, 2022
Atmospheric rivers across Australia in 2020 appear as wispy white clouds in this infrared satellite weather image.
Image credit: courtesy Kimberley Reid and Himawari-8/Met Agency
Although they have been around for millennia, atmospheric rivers have only been discovered by humans in the last 25 years.
In February 2022, cubic kilometers of water were dumped on the city of Brisbane. An atmospheric river is a narrow, rapid current of moist air. It can be several thousand kilometers long and a few hundred kilometers wide. It’s a giant, invisible conveyor belt of water in the sky, moving over and across the planet.
At any given time, there are about a dozen of these atmospheric phenomena across the globe – most of them over water. But, unlike an earthly river, they are not fixed. Instead, they continually form, fade, reform and evolve. So they come and go.
Atmospheric rivers are essential to the water cycle. They displace 90% of the water vapor in the air, but cover less than 10% of the planet. A large atmospheric river can move a quarter of a million tons of water every second past a given point. If one gets really big, it can be disastrous.
In 1862, an atmospheric river transformed central California into a temporary inland sea 500 km long and 30 km wide. Not only did thousands of people die, but also a quarter of the 800,000 head of cattle in California at the time.
Sacramento, the state capital, was inundated with more than three meters of muddy water and took six months to completely dry out. At that time, California was bankrupt. And just for a little extra ecological impact, the water in San Francisco Bay has changed from salt water to fresh water.
The atmospheric river that hit the east coast of Australia in March 2021 left several dead, forced the
evacuation of more than 24,000 people and cost the Australian economy an estimated $652 million.
Greenhouse gases generated by human activity now capture the heat of an additional 600,000 Hiroshima atomic bombs every day. This means that the amount of heat and moisture transported by atmospheric rivers is much higher than in the recent past.
A quarter of a century ago, we didn’t know atmospheric rivers existed, let alone that climate change would make them worse. Who knows what other surprises climate change has in store for us?