Climate change could unleash 'rivers in the sky', researchers warn

Climate change will lead to more extreme weather around the world - and will lead to an increase in a phenomenon known as ‘rivers in the sky’, researchers have warned.

‘Atmospheric rivers’ are long, narrow bands of concentrated water vapor flowing through the atmosphere.

When a ‘river in the sky’ meets a barrier, such as a mountain range, it can produce extreme levels of rainfall or snowfall.

The University of Tsukuba say that while their study investigated East Asia, ‘rivers in the sky’ could also become more common over Europe.

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Lead author Professor Yoichi Kamae says, "To investigate the behaviour of atmospheric rivers and extreme precipitation over East Asia under projected climate warming, we used high-resolution global atmospheric circulation model simulations as well as regional climate model downscaling simulations.

“We compared simulations based on historical meteorological data from 1951 to 2010 with future simulations based on the year 2090 under a climate scenario with 4 degrees Celsius of warming of the global-mean surface air temperature."

The simulations predicted unprecedented, record-breaking rainfall events in parts of East Asia, greatly affected by atmospheric river phenomena.

The greatest amounts of atmospheric river-related precipitation occurred on the southern and western slopes of mountains in East Asia, including in Japan, the Korean Peninsula, Taiwan, and northeastern China, with the greatest rainfall on the southwestern slopes of the Japanese Alps.

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Professor Kamae said, "Our findings are likely also applicable to other regions of the mid-latitudes where interactions between atmospheric rivers and steep mountains play a major role in precipitation, such as in western North America and Europe. These regions may also experience more frequent and intense extreme precipitation events as the climate warms."

Last year’s UN climate change report warned that extreme weather events like heatwaves and droughts which previously would have happened every 50 years could soon happen every four.

The report was the first to quantify the likelihood of extreme events across a wide variety of scenarios.

The researchers also warned that other ‘tipping point’ events are a possibility.

The researchers wrote: “Abrupt responses and tipping points of the climate system, such as strongly increased Antarctic ice sheet melt and forest dieback, cannot be ruled out”.

Dr. Robert Rohde, Lead Scientist of Berkeley Earth said: “What were once-in-50-year heat extremes are now occurring every 10 years.

“By a rise of two degrees celsius, those same extremes will occur every 3.5 years.”

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The report found that (for example) once-in-a-decade heavy rain events are already 1.3 times more likely and 6.7% wetter, compared with the 50 years leading up to 1900 when human-driven warning began to occur.

Droughts that previously happened once a decade now happen every five or six years.

Xuebin Zhang, a climatologist with Environment Canada in Toronto warned that as the world warms, such extreme weather events will not just become more frequent, they will become more severe.

Zhang said that the world should also expect more compound events, such as heat waves and long-term droughts occurring simultaneously.

Zhang said, “We are not going to be hit just by one thing, we are going to be hit by multiple things at the same time.”

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