Global warming caused Hokkaido to receive up to 20% more snow than average in December 2021, according to a team of Japanese scientists.
A study led by Tomonori Sato of Hokkaido University’s Faculty of Environmental Earth Science found that while climate change is generally expected to reduce the amount and duration of snowfall in the long run, it can result in sporadic snow events that are more intense in some areas. Its findings were published Monday in the Journal of Geophysical Research: Atmospheres.
The team analyzed snowfall that occurred in Hokkaido over Dec. 17 and 18 in 2021, which resulted in a 24-hour snow accumulation of over 50 centimeters in the cities of Sapporo and Otaru — a record at the time. Several snow events that followed in the region, continuing through February 2022, caused massive road congestion and the suspension of railway services for several days between Sapporo and Shin-Chitose Airport.
The scientists concluded that the heavy snow of that period was caused in two stages, and both were made stronger by climate change.
In the first stage, the passing of a low-pressure system accompanying the south wind brought large volumes of warm air and vapor, which resulted in large parts of eastern Hokkaido experiencing 20% more snow than usual.
In the second stage, as the weather transitioned into a typical winter atmospheric pattern marked by high pressure in the west and low pressure in the east, a band of strong updraft clouds emerged, which resulted in 10% more snowfall on the Sea of Japan coast.
The researchers first identified days in the past with similar weather patterns by using a machine-learning method called Self-Organizing Maps, which automatically classifies maps of daily weather. The weather pattern of Dec. 17 to 18 that year resulted in a low-pressure system developing in the Sea of Japan that traveled through the south of Hokkaido to reach the Kamchatka Peninsula in Russia.
The scientists then used a large climate database called d4PDF (or database for Policy Decision making for Future climate change), which simulates both present-day weather conditions and hypothetical scenarios not affected by global warming, to estimate how much climate change had affected the temperature and moisture levels on those selected days.
They also conducted high-resolution simulations by inputting air temperature, vapor amount and ocean temperature data into a 2-kilometer-grid weather model.
These simulations reproduced snowfall patterns under current conditions and compared them to patterns that excluded the effects of global warming.
The research — part of a growing field of climate science called event attribution — revealed that the December 2021 snowfall was 10% to 20% higher than usual as a result of a warming of the atmosphere and the ocean.
“The methods developed in this study can be applied to analyze all extreme weather events around the world,” the researchers wrote in a statement. “In the future, we hope to expand the scope of our research to heavy rainfall in the warm seasons and improve ways to search past days with similar weather patterns.”