Photo/IllutrationMembers of the Self-Defense Forces try to clear the way after a record heavy snowfall hit Iiyama, Nagano Prefecture, in 2006. (Asahi Shimbun file photo)

The probability of “once in a lifetime” heavy snowfalls could increase fivefold in mountainous areas on the Sea of Japan side if global warming continues at its current pace, according to Japanese researchers.

The team, consisting of scientists from Tohoku University and the Meteorological Research Institute of the Japan Meteorological Agency, on Dec. 16 announced the results of the study that used supercomputer simulations.

The study took into account the 1-degree rise in temperatures from the level before the Industrial Revolution, as well as a prediction by an international panel on climate change that average global temperatures could increase by up to 4.8 degrees by the end of the century.

The team simulated three scenarios for the area from the Tohoku region in the north to the southern main island of Kyushu: no change in current temperatures, which have already risen by 1 degree; a rise of 2 degrees from the pre-Industrial Revolution level; and an increase of 4 degrees from that level.

In the worst-case scenario, a 4-degree increase would make heavy snowfalls of more than 60 centimeters five times more likely to occur in mountainous areas from the southern part of Yamagata Prefecture to Gifu Prefecture in central Japan, according to the study.

“Such heavy snowfalls, which currently happen around once in 42 years, could occur with a higher probability of once in eight or nine years,” said team member Takahiro Sasai, an assistant professor at Tohoku University specializing in meteorology.

However, heavy snowfalls could decrease on the Pacific Ocean side of Japan under the same conditions, Sasai said.

Warmer temperatures cause more sea water to evaporate, leading to an increase in the amount of water vapor in the air. In addition, cold air is believed to be flowing south more frequently from the Arctic Circle.

When the cold air meets the rising water vapor in mountainous areas, the mix can create snow clouds. Therefore, an increase in both cold air currents and water vapor would result in heavier snowfalls, the team said.

The results of the team’s study were published in the online Journal of Geophysical Research: Atmospheres on Dec. 16.

A report by the Intergovernmental Panel on Climate Change (IPCC) of the United Nations forecasts that if no measures are taken against global warming, average temperatures would shoot up by a maximum 4.8 degrees by the end of the century, compared with the level before the Industrial Revolution.

If that happens, sea levels would rise by 61 to 110 centimeters, compared with levels between 1986 and 2005, the IPCC report said.

A separate study by a research team that included scientists from the University of Tokyo showed that if temperatures rise by 4.8 degrees, Japan, including the Hokuriku and Tohoku regions, would experience more frequent heavy rainfalls, like the torrential rain that flooded wide areas of the western part of the country last year.