Japan’s record heat in July ‘almost impossible’ without climate change

The extreme heat felt across Japan in July was “almost impossible” without global warming, a joint analysis by the Meteorological Agency and the education ministry has found.
In addition, the heavy rainfall that caused severe floods in northern Japan later that same month, mostly in Yamagata and Akita prefectures, was also exacerbated by climate change, the researchers said in a report released earlier this week, using the “event attribution” method.
Event attribution is a relatively new field of study, in which scientists calculate the role climate change plays in extreme weather events by creating simulations that compare current climate conditions to a world free of greenhouse gas emissions.
The researchers concluded that the warming-induced rise in temperatures and the resulting surge in water vapor increased the volume of rain in Akita and Yamagata by 20% or more.
This year’s summer months of June through August were hotter than usual, resulting in record temperatures in July, a trend that continued in western Japan last month.
On July 29, for example, the mercury hit 41.0 degrees Celsius in the city of Sano, Tochigi Prefecture, nearly tying with a record high of 41.1 C logged in the city of Kumagaya, Saitama Prefecture, on July 23, 2018, and the city of Hamamatsu, Shizuoka Prefecture, on Aug. 17, 2020.
Also, between July 1 and Aug. 31 this year, 144 out of 914 weather observation spots either exceeded or tied with previous highs.
The extreme heat was caused by various meteorological conditions, including rising sea surface temperatures around Japan. The event attribution analysis found that, under present climate conditions, extreme heat events such as the one in July are likely to happen every 10 years. Under simulated climate conditions that did not factor in the effects of global warming, such events “would have been almost impossible,” the report says.
Likewise, during the torrential rain that lashed the Tohoku region from July 24 to 26, two observation points in Yamagata recorded rainfall surpassing 400 millimeters over a 48-hour period — by far the most on record.
The meteorological agency says that this unusual rain was caused by a mix of conditions: large volumes of water vapor sandwiched between a high-pressure zone in the Pacific Ocean and Typhoon Gaemi — referred to as Typhoon No. 3 by the Meteorological Agency — was pushed northward, resulting in heavy rain in northern Japan; and the evaporation of water around Okinawa Prefecture and the Amami region of Kagoshima in southern Japan, which provided large volumes of water vapor in the lower atmosphere.
According to the Yamagata Prefectural Government, three people died and four people were injured due to rain in the prefecture in July, while nearly 1,800 homes were destroyed or inundated with water.