Japan Data

Japan Braces for Rainy Season After Last Year’s Disastrous Downpours


The rainy season begins across much of Japan in early June. In 2018, widespread torrential rain caused severe damage in the west of the country.

Rainfall Varies Year to Year

The following chart shows the start and end of rainy season in each region in 2018, as well as the average annual dates. Hokkaidō is not greatly affected by rainy season, and so is not included.

2018 Rainy Season Dates and Average Annual Dates

Start of Rainy Season 2018 End of Rainy Season 2018 Average Starting Date Average Ending Date
Okinawa June 1 June 23 May 9 June 23
Amami Ōshima May 27 June 26 May 11 June 29
Southern Kyūshū June 5 July 9 May 31 July 14
Northern Kyūshū June 5 July 9 June 5 July 19
Shikoku June 5 July 9 June 5 July 18
Chūgoku June 5 July 9 June 7 July 21
Kansai June 5 July 9 June 7 July 21
Tōkai June 5 July 9 June 8 July 21
Kantō Kōshin June 6 June 29 June 8 July 21
Hokuriku June 9 July 9 June 12 July 24
Southern Tōhoku June 10 July 14 June 12 July 25
Northern Tōhoku June 11 July 19 June 14 July 28

On average, rainy season starts from early June from Southern Kyūshū through Fukuoka, Osaka, and Nagoya to the greater Tokyo area, and ends one and a half months later in late July. Rainy season precipitation in Kyūshū is around 500 millimeters, making up one quarter of the region’s annual rainfall, while the Kantō Kōshin and Tōkai areas receive 300 millimeters of rain, accounting for one fifth of those regions’ annual rainfalls, respectively.

The below chart shows precipitation during rainy season over the last 30 years in Kantō Kōshin. The figures vary greatly depending on the year, including cases such as in 1990 when there was a dry rainy season in which only half the average annual rainfall was recorded.

Huge Damage in Western Japan in 2018

Toward the end of each rainy season, the volume of rain gets heavier and frequent severe downpours can cause damage due to rivers flooding and landslides. Between June 28 and July 8, 2018, there was record widespread rainfall, particularly across western Japan, with some areas receiving more than 1,800 millimeters of precipitation.

The death toll in the 2018 Japan floods came to more than 220 and according to Cabinet Office data, approximately 17,000 houses were either totally or partially destroyed, while 30,000 houses were flooded.

Aerial view of Kurashiki City, Okayama Prefecture, taken the morning of July 8, 2018. (© Jiji)
Aerial view of Kurashiki City, Okayama Prefecture, taken the morning of July 8, 2018. (© Jiji)

(Translated from Japanese. Banner photo © Ushico/Pixta.)

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