‘Rivers in the sky’

Scientists have warned of ‘rivers in the sky’ over East Asia because of warming climate.

Atmospheric rivers (ARs) are long, narrow columns of water vapour flowing through the sky that pick up moisture from warm areas and deposit it in colder regions. When they hit a barrier like a mountain range, it can lead to extreme levels of rain or snowfall.

This weather phenomenon is thought to contribute around 20 per cent of the Earth’s total water flow.

But, with vast quantities of water being released in a short space of time, they can also cause potentially catastrophic flooding. Wind and temperature control their movements too – both factors that are influenced by climate change.

While there has been a lot of research into atmospheric rivers, it isn’t entirely clear what our changing climate will do to them. But meteorologists say that, with more frequent extreme weather having a severe impact on society, understanding how they will be affected is vital.

To find out, scientists at the University of Tsukuba in Japan ran simulations using nearly 60 years of weather data. Computer models showed that if we see the worst outcomes of climate change, atmospheric rivers would cause record-breaking amounts of precipitation in Japan, Taiwan, northeastern China and the Korean Peninsula.

“Atmospheric rivers will bring unprecedented extreme rainfall over East Asia under global warming,” says a newly published paper.

In July 2018 and July 2020, East Asia suffered from extremely heavy rainfall events. The heavy rainfall was observed over a broad area because of organised water vapour flow associated with atmospheric rivers. ARs received increasing attention over the past decade because of such hazardous events. 

Under global warming, water vapour transports by ARs are enhanced. Using a set of global and regional atmospheric model simulations, scientists assessed the great role of ARs in the future extreme rainfall events. ARs with increased water vapour will bring record-breaking extreme rainfall when they make landfall over China, the Korean Peninsula and Japan. Such a great importance of ARs may also be found over other mid-latitude regions, including western North America and Europe.