Kyushu floods: Sign of things to come?

While Europe and the Middle East swelter under record temperatures, the southern island of Kyushu in Japan has been devastated by floods caused by extreme rainfall. Evacuation orders or advisories have been issued targeting close to 2 million people in Kagoshima, Miyazaki and Kumamoto prefectures. More than 1,000 mm of rain has fallen on Kyushu in the past week. The average annual rainfall in Kagoshima is about 2,300 mm – it is a wet place even normally – which means the southernmost prefecture of the island has seen almost one half of its annual precipitation fall within just one week. The weekly amount is more than double the monthly average for July.

JMA weather analysis map 6 July 201

The rains have brought on heavy floods and overflowing rivers in the mountainous region. Landslides have already caused at least two casualties, as two women had their homes overtaken by mudflows in two separate incidences on Monday and Thursday. News broadcasts on the national Japanese NHK channel show mountain sides slipping away bringing along big trees and entire forest patches to the valleys. Cars and houses have been inundated by mud. The Japan Meteorological Agency (JMA) says that a highly moist and warm seasonal front hovering above Kyushu is causing heavy rainclouds to form above the island and affecting areas in western and central Japan.

In 1993, Kyushu experienced the most devastating rainfall caused disasters in history. That cool summer, the rainy season was exceptionally long and the peak of torrential rains took place in early-August. Then, too, parts of Kyushu experienced rainfall of more than 1,000 mm. A veteran Asahi Shimbun correspondent who was then based in the paper’s Kagoshima office recalls the devastation, with cars piled up by the flowing water, even a twisted train. Debris flows caused large damage: there were 22 major ones, especially in the coastal areas where the mountains run into the sea, and where the major roads and railways are located. Some 2,500 people were trapped in cars, buses and trains, and had to be evacuated by boat.

Although this is officially tsuyu, or the rainy season, the amount of rain received in Kyushu is exceptional – except that the same happened a year ago. On 28^th of June 2018, a non-tropical low front became stationary over Japan. Then, too, several areas received more than 1,000 mm of rain in a short period of time. That time the worst hit areas were in western parts of the main island of Honshu, from Hiroshima and Nagasaki to Kyoto, with Tottori and other areas on the Sea of Japan getting their share. At least 225 people were confirmed dead in the related mudslides and landslides and having their vehicles swept away by floods. In worst affected areas, the flood waters rose to 5 meters. The rains finally eased during the second week of July when also the temperatures soared. More than 11,000 households were left without electricity and, thus, without air conditioning and clean water.

The previous year, in 2017, torrential rainfall and floods left 155 people dead and forced the evacuation of two million people, mostly in Kyushu. At that time, it was the most devastating rain-related event in Japan in nearly three decades.

As I write this, rainfall is continuing in the south. Where I sit, in Iwate prefecture in the north of Honshu, the rain is a light drizzle interspersed with sunshine. The temperature is mercifully cool. The question on my mind is whether these exceptional weather anomalies are linked to climate change. There is some evidence that this would be the case, as warming sea surface in areas of the East China Sea pushes the seasonal rain front and warm air northward to Japan even when the rainy season is officially over. The JMA’s annual climate change monitoring report published in October 2018 recorded unusual weather conditions on the Pacific side of Japan, while mean temperatures were significantly higher than normal in the Okinawa-Amami islands. In a press release on the primary factors contributing to the heavy rains in July 2018, the same Agency concluded that:

“The long-term trend of increased intensity in observed extreme precipitation events in Japan and the clear upward trend in amounts of airborne water vapor also suggest that the Heavy Rain Event may be linked to global warming. Global warming and ongoing higher-than-normal zonally averaged tropospheric air temperatures associated with the northward shift of the subtropical jet stream are also considered responsible for the extreme heatwave.”

According to WWF, the impacts of climate change are already being felt in Japan, i.a. in terms of increased frequency and intensity of heavy rains and other extreme weather events.

Japan is a country that is likely the best prepared in the world to cope with natural hazards and disasters. Still, climate change will provide – and is already doing so – challenges that will be costly to the government and the private sector, as well as every person inhabiting these islands in the Pacific Ocean.

Reports referred to in this blog include:

Primary Factors behind the Heavy Rain Event of July 2018 and the Subsequent Heatwave in Japan from mid-July Onward. Japan Meteorological Agency (22 Auguste 2018)

Climate Change Monitoring Report 2017. Japan Meteorological Agency (October 2018)

Nippon Changes. WWF (no date)

In addition, I’ve used news reporting by NHK, Mainichi Shimbun, Asahi Shimbun, The Japan Times, BBC and NPR.