For the past several years, every time there has been a disaster, we hear in the news that it was a, "once in a generation” event, or, an “unprecedented” torrential rain or a heat wave. Television and newspapers call these “abnormal" weather events. However, in the scientific world, if it happens every year or once every few years, it is not actually abnormal weather. Instead, the term "extreme events" (extreme weather) is increasingly being used, and the IPCC report also uses this term.

The record heat wave in Russia in the summer of 2010, and the drought in the Amazon in 2010, as well as the wildfires on the U.S. West Coast in 2020, are regularly attributed to extreme heat caused by global warming. In Japan, “guerrilla” rainstorms, in which a lot of rain falls at once, and linear precipitation zones, in which heavy rain continues to fall only in certain areas, are examples of extreme weather events. In addition, super-sized typhoons are more common, and they often sustain their intensity as they approach Japan. Extremes are found not only rain, but also heat. While the number of midsummer days with a maximum temperature of 30°C or higher are not increasing, the number of extremely hot days with a maximum temperature of 35°C or higher have been steadily increasing over the past decade (see Episode 1). Without doubt, extreme and unusual weather conditions are threatening our daily lives.

The IPCC report attributes these extreme phenomena (extreme weather events) to the fact that we humans have caused global warming by emitting large amounts of carbon dioxide. Researchers around the world are now using supercomputers to simulate and study whether extreme weather events are related to global warming. The latest research indicates that some extreme weather events are more likely to occur as a result of global warming than others, and that the relationship is not yet clear. Further long-term research is underway to obtain more reliable results on the relationship between global warming and extreme weather events.

※ IPCC: Intergovernmental Panel on Climate Change.

episode 7
In Some Places Torrential Rain, In Other Places Drought. What is Happening?

Detailed data and explanations 1:
The number of annual occurrences of 1-hour precipitation of 50 mm or more recorded by AMeDAS ( Japan’s Automated Meteorological Data Acquisition System)

Source: Japan Meteorological Agency
( https://www.data.jma.go.jp/cpdinfo/extreme/extreme_p.html )

In meteorological terms, rainfall of 50 mm or more per hour is described as "extremely heavy rain. This type of rainfall can be equated to being more like a waterfall than pouring a bucket of water. The frequency of such rains has been increasing with each passing year. Comparing the last 10 years to 35 years ago, the number of such rainfalls has increased about 1.4 times.