Rainy Season in 2024 Brings Risk of Torrential Downpours in Japan

The chart below shows the beginning and end of the rainy season in various regions of Japan in 2023, as well as the beginning and end in an average year. Last year, tsuyu began in northern Kyūshū, Chūgoku, Shikoku, Kansai, and Tōkai all on the same day of May 29, around a week earlier than average. It was the first time in 10 years that Tōkai and Kansai saw the rainy season start in May.

The end of tsuyu was declared in Okinawa and Amami Ōshima in late June, followed by Shikoku, Chūgoku, Kansai, and Tōkai in mid–July, while in Hokuriku, Kantō Kōshin, and Tōhoku, it ended around July 21 to 22. Kyūshū was later than average, on July 25.

In an average year, the rainy season begins in early June in areas from northern Kyūshū to Kantō Kōshin—which includes the cities of Tokyo, Osaka, Nagoya, and Fukuoka—and ends around July 20. Precipitation for this period is around 500 to 600 millimeters in northern Kyūshū and 300 millimeters in the Kantō Kōshin and Tōkai regions.

Precipitation Varies from Year to Year

The figure below shows the amount of precipitation in the Kantō Kōshin region over the past 30 years in comparison to the amount in an average year. It can be seen that this varies considerably from year to year. For example, during the rainy season in 1990, the Kantō region saw only half the normal amount of rainfall. In contrast, the 2020 rainy season stretched until August 1, with 1.7 times the normal amount of precipitation.

Precipitation is heavier during the rainy season, particularly toward the end, so it is important to stay fully vigilant of river floods and landslides that can be caused by torrential downpours.

(Translated from Japanese. Banner photo: The aftermath of a landslide that hit Kurume in Fukuoka Prefecture on July 10, 2023. © Jiji.)