RAINY SEASON IN JAPAN
wysteria, the rainy season flower Before the arrival of real summerlike weather, Japan has a damp rainy season known as tsuyu. From May until July, there is a highpressure mass of cold air above the Sea of Okhotsk to the north of Japan, while over the Pacific Ocean there develops a high-pressure mass of warm, moist air. Along the line where these cold and warm air masses meet, known as the baiu zensen, or “rainy season front,” there often develop areas of low-pressure warm air. Thus the baiu zensen, which extends from southern China over the Japanese archipelago, causes prolonged periods of continuous rainfall. After the middle of July, high-pressure air masses over the Pacific Ocean become predominant and the rainy season comes to an end as the baiu zensen is pushed northward.
The humid rainy season---caused by the Bai-u front with also brings rain to Korea and southern China---lasts for about a month, from mid-June to mid-July in most parts of the country. But because Japan is strung out over such a large area latitude-wise the rainy season ends in Okinawa in June around the time it in starts Hokkaido and northern Japan. On most days of rainy season it rains for one two hours or less. The temperatures are significantly cooler than later in the summer.
In the summer of 2009 the seasonal rain front stalled over Japan bringing heavier-than-usual rains, a longer rainy season and cooler temperatures and even spawned a couple of tornados. In some places where the rainy season usually ends by mid July it extended into August. These conditions were caused the weakness of the Pacific high and its slow development which was tied to weak ariel convection activity near Philippines.
The typhoon season lasts from late summer to early autumn. Most typhoons that strike Japan arrive in September and generally come ashore in southern Japan and dissipate as they move north. A summer heat wave sets on after the June rainy season is over In many places it is very hot with little relief many days in a row.
Websites and Resources
Links in this Website: LAND AND GEOGRAPHY OF JAPAN Factsanddetails.com/Japan ; CLIMATE AND WEATHER IN JAPAN Factsanddetails.com/Japan ; STORMS, FLOODS AND SNOW IN JAPAN Factsanddetails.com/Japan ; TYPHOONS Factsanddetails.com/Japan ; TYPHOONS IN JAPAN Factsanddetails.com/Japan ; NATURAL RESOURCES AND JAPAN Factsanddetails.com/Japan
Good Websites and Sources on Climate and Weather: Good Photos of the Seasons at Japan-Photo Archive japan-photo.de ; Statistical Handbook of Japan Land and Weather Chapter stat.go.jp/english/data/handbook ; 2010 Edition stat.go.jp/english/data/nenkan ; News stat.go.jp Japan Meteorological Agency Japan Meteorological Agency ; Weather Underground wunderground.com/global/JP ; Weather Channel Weather Channel ;World Climate World Climate ; Accuweather Accuweather ; Climate Data climatetemp.info/japan ;Wikipedia article on Geography of Japan Wikipedia ;
Good Websites and Sources of Storms and Floods: Weather Warnings from Japan Meteorological Agency jma.go.jp/en/warn ; Marine Warnings from Japan Meteorological Agency jma.go.jp/en/seawarn ; Wikipedia article on Snow Country in Japan Wikipedia ; Landslide Distribution Map bosai.go.jp/en ; BBC Picture Gallery of Flood in Japan news.bbc.co.uk ; Academic Paper of Flood Maps in Japan internationalfloodnetwork.org ; Tornados in Japan Survey by the American Meteorological Society ams.allenpress.com ; BBC report on 2006 Tornado bbc.co.uk
Typhoons: Typhoon and Hurricane Basics aoml.noaa.gov ; Data and Images from Pacific Typhoons eorc.jaxa.jp/ADEOS Typhoon and Hurricane Satellite Images and Photos fotosearch.com ; Video from Nasty Typhoon in Taiwan YouTube ; Typhoon Video YouTube ; Central Pacific Hurricane Center at the National Weather Service prh.noaa.gov ; Wikipedia article on Tropical Cyclones Wikipedia ; National Hurricane Center at the National Weather Service nhc.noaa.gov ; Jet Propulsion Laboratory Images of Typhoons jpl.nasa.gov/images ;
Typhoons in Japan : Typhoon and Tropical Cyclone Information from the Japan Meteorological Agency Japan Meteorological Agency ; Video of Typhoon Surfing in Japan YouTube ; Brochure on Typhoons in Japan pdf file rms.com/Publications ; Good Japan Times article on Typhoons in Japan search.japantimes.co.jp ; Digital Typhoon Information from the and United States Navy agora.ex.nii.ac.jp/digital-typhoon ; Ise-Wan Typhoon Wikipedia article on the 1959 Ise-wan Typhoon (Typhoon Vera) wikipedia.org/wiki/Typhoon_Vera ; U.S. Navy Report on the 1959 Ise-wan Typhoon pdf file usno.navy.mil and usno.navy.mil ; Lessons from the Isewan Typhoon pdf file katrina.lsu.edu/downloads/Typhoon_Isewan
Rainy Places in Japan
uliyo-e by Hokusa Yakushima, a small Japanese island 560 miles south of Tokyo and just south of Kyushu, is one of the wettest places on earth, receiving 10 meters (394 inches) of rain annually. The rain is caused by a 6,000 foot mountain that traps clouds and forces them to release their moisture. Describing the weather in 1995, one of the island's 14,000 residents told Reuter, "It rained literally non-stop for two months and that was after the rainy season ended.”
Yakushima had once hoped to sell its abundant water supplies to the Middle East but those plans were scrapped with the development of giant desalinization plants. The island now does all right with fish farming and tourism, attracting visitors with red-faced monkeys, sea turtles, 3,000-year-old Shamanist traditions, a giant tree and hikes through dripping rain forests. See Places
In November 2011, Kyodo reported: “A record downpour in the area of Setouchi on Amami-Oshima Island, Kagoshima Prefecture, prompted the city to recommend all of its 5,500 households---10,000 residents---to evacuate. No injuries had been reported, according to local police. Rainfall measuring 143.5 mm per hour through 9:08 a.m. was observed in the town, marking the ninth-largest recorded rainfall per hour in the nation's history. [Source: Kyodo, November 3, 2011]
“Its neighboring municipalities, including the city of Amami, were also hit by heavy rains---more than 120 mm per hour, according to the Meteorological Agency. The Kagoshima Prefectural Government said that by noon, a total of 148 people in Setouchi and Amami had evacuated their homes. According to local police, the rains also prompted a landslide in Setouchi around 8:30 a.m., pouring mud into a medical clinic in the town. Eighteen patients were in the clinic at the time, but no one was reported injured. The area also suffered heavy rain last year leading to flooding and the closure of a tunnel in Amami. [Ibid]
Heavy Rains and Floods in Japan
The number of heavy rainfalls---over 100 millimeters per hour---doubled from 2.2 times a year between 1976 to 1995 to 4.7 times a in the past decade. The concreting of rivers in municipalities has made flash floods very dangerous. Rain runs off into rivers quickly and builds up speed rapidly as there is no soil or vegetation to slow the water down.
The Tokyo subway system is regarded as vulnerable to a serious flood. Nearly 70 percent of all the subway tracks could flooded in the event of a heavy, prolonged rained that causes rivers to burst through levees and overflow their banks. Experts such an event could occur if about a meter and half of rain falls over a three day period.
In 1938, 700 died or went missing in the Great Hanshin Flood that hit Kobe and surrounding areas. In July 1982, a flood in Nagasaki produced by 187 millimeters of rain in a single day killed nearly 300 people. Major landmarks such as the Meganebashi Bridge were washed away. The owner of a busy restaurant that was inundated with 2.2 meters of water told the Yomiuri Shimbun, she heard a deep roar: “It was the sound of the river’s raging water, although I did not realize what it was. It was really scary.”
In August 1999, 13 people who camped on an island in the Kurokauragawa River in Kanagawa Prefecture were swept away and killed after torrential rains caused the river to quickly rise and cover the island. Five people on the island were rescued. The campers had been warned that the river was going to flood but didn't respond.
In July 2003, landslides and floods triggered by torrential rains during the summer rainy season left 22 dead in Kyushu. Damage around the city of Minamata was the worst. Hundreds of troops and firefighters were employed in a search for missing people. The same storm, which dropped up to four inches of rain an hour is some places, derailed a train in Nagasaki and flooded subways stations in Fukuoka.
Landslides, Other Dangers Associated with Heavy Summer Rains in Japan
landslide The Yomiuri Shimbun reported: “A phenomenon called guerrilla rain’sudden downpours into relatively narrow zones, mainly in urban areas---has attracted attention in recent years. Such rain is caused mainly by cumulonimbus clouds that form in a clash of warm and cold air. But some experts think the urban heat island phenomenon and global warming trends have a causal relationship to the sudden downpours. [Source: Yomiuri Shimbun, July 17, 2010]
“Guerrilla rain is frightening in that it is difficult to predict and the damage it causes occurs all at once. In the summer of 2008, five workers died in Tokyo after being washed away by a surge in sewer water while working underground. Also that summer, a swollen river killed five people, including primary school children, in Kobe. [Ibid]
“There are also landslides. In recent years, experts have attributed large-scale mudslides to the so-called deep-seated landslide mechanism. Heavy rain soaks into cracks in the bedrock, which has been weakened over time, and when the bedrock collapses downhill, it takes a large volume of upper soil with it. Unlike shallow landslides, which can be prevented to a certain degree through good forestry practices, there are no known measures to prevent the occurrence of deep-seated landslides. We consider it necessary to urgently study what steps could be taken. [Ibid]
About 200 people are killed every year in Japan in rain-related disasters. A flash flood caused a storm that dropped 23 millimeters of rain in a short period of time produced a flash flood that killed four people in Kobe in July 2008. Three of the victims---an adult and two children---were members of school group playing on the banks of the Togagawa River when the flash flood struck. Others were swept away and rescued. The Togagawa River in Kobe is lined with concrete. Water levels in the river rose 134 centimeters in 10 minutes.
In July 2007, heavy rains associated with the seasonal rain front caused landslides and river flooding in Kyushu. One train was derailed by a landslide of mud and trees. No serious injuries were reported.
In July 2006, mudslides caused by heavy rains associated with the rainy season killed 20 people in Nagano, Fukui, Shimane and Okayama prefectures and forced e evacuation of almost 15,000 people from 5,322 homes. Three people were killed when a flash flood washed away their home. Landslides and mudslides swallowed up and carried away homes. A levee broke in one place. Rain in some places was over 500 centimeters over several days. Some places received four centimeters of rain an hour. One place in Nagano Prefecture received 61.3 centimeters of rain.
Deep-Seated Landslides in Japan
During a flood disaster in September 2012, the Yomiuri Shimbun reported, deep-seated landslides occurred in 76 locations in the Kii Peninsula, resulting in the loss of about 80 million cubic meters of soil, according to a survey by the National Institute for Land and Infrastructure Management and others. The amount of soil lost, equivalent to 80 percent of the earth that moved in the landslides, is believed to be the country's largest since the end of World War II. [Source: Yomiuri Shimbun, September 8, 2012]
The institute, based in Tsukuba, Ibaraki Prefecture, examined aerial photos and satellite images of about 4,800 square kilometers where damage from landslides was severe in Wakayama, Nara and Mie prefectures. Combining its analysis with field studies, the institute estimated the number of locations where landslides occurred and the total amount of soil lost. In the areas covered by the survey, landslides occurred in 3,077 locations during the disaster, causing a total of 100 million cubic meters of soil to collapse in plots totaling about 10 square kilometers. [Ibid]
Deep-seated landslides, in which the bedrock beneath the topsoil collapses and moves a large amount of soil, occurred in 76 locations. Such landslides are often triggered by heavy rains over a prolonged period. During the disaster in the Kii Peninsula, villages in Tanabe, Wakayama Prefecture, and Gojo, Nara Prefecture, were buried in soil and mud sliding off mountains, causing many casualties. While deep-seated landslides accounted for just 2.5 percent of all the landslides during the disaster, they led to serious damage. Such landslides were responsible for about half of the collapsed areas and released 80 percent of the soil lost during the floods. Furthermore, in 17 of the deep-seated landslide locations, landslide dams that halt the flow of a river and increase the risk of mudslides were created. "The volume of deep-seated landslides reflects that large areas in the Kii Peninsula were pounded by a record amount of rainfall," an official at the institute said.
Safety Measures to Deal with Heavy Summer Rains
The Yomiuri Shimbun reported: “To prevent damage from heavy rain, it is essential to have highly accurate weather forecasts and to issue appropriate warnings. Such information must be adequately conveyed by local governments to residents in affected areas. It is imperative that those residents be advised to evacuate if necessary as soon as possible. [Source: Yomiuri Shimbun, July 17, 2010]
The Land, Infrastructure, Transport and Tourism Ministry has started introducing advanced radar systems capable of accurately measuring the strength of precipitation mainly in major cities. Such radar can also be used to predict situations in wide areas affected by heavy rain. There also are private-sector services offering guerrilla rain forecasts on mobile phone sites. Between late May and mid July 2010, the Meteorological Agency has issued warnings and advisories on heavy rain and floods in a much more detailed manner as it increased the number of forecasting areas from 375 to 1,777 to correspond to each municipality. [Ibid]
Heavy Rains in 2008, 2009 and 2010 in Japan
landslide Heavy rains in August 2008, caused severe damage, particularly in Aichi Prefecture, and generated floods and landslides in several location around Nagoya and Tokyo. New hourly precipitation records were set in 32 locations.
Rainfall in Okazaki in Aichi Prefecture reached 148 millimeters per hour, the seventh highest on record. In Tokyo itself more than 700homes were flooded. Two people were killed: an 80-year-old swept way by a swollen river in Okazaki and a 73-year-old woman who died when her flooded house. The body of the 80-year-old woman was found 40 kilometers from her home.
Waters in Okazaki reached waist-level. Some train lines were flooded, causing passengers to spend the night in the trains. The rain came from storms caused by warm humid air over particularly warm water channeled toward the Nagoya and Tokyo area between stalled high- and low- pressure systems off the coast of eastern Japan.
The heavy rains were attributed to “snaking westerlies”---winds that undulate north and south like a snake while moving towards the east---as opposed to the normal west-to-east westerly winds. The snaking pattern was caused by the movement of a large high pressure cell which usually sits over Japan in the summer to the Pacific off of Japan. This caused a front to form over Japan on which cold air from Russia slammed into warm and moist air from the south, producing heavy rains. The same pattern brought rains to Beijing for the Olympics.
In July 2009, ten people were killed in Fukuoka Prefecture in northern Kyushu in floods, mudslides and landslides caused by heavy rains. The dead were swept away by rain-swollen rivers and swallowed up in mudslides that engulfed their homes. A large landslide blocked the Kyushu Expressways. Some places received more than 600 millimeters of rain in less than 24 hours. Around the same time, 16 people were killed in Yamaguchi Prefecture, many of them elderly people killed when a mudslide inundated a nursing home.
Heavy rains during the summer rainy season in 2010 caused some severe damage and killed several people. One bout of intense rain in mid July killed 13 people in Gifu, Hiroshima and Shimane Prefecture. Some of the victims were swept away by swollen rivers. Others were in homes engulfed by mudslides. Two victims were killed in a house in Matsue struck by four-meter-wide boulders.
Heavy rains in October 2010 on Amami island killed three people, downed power lines and caused landslides. More than 2,000 people were cut off by landslides and floods. Large amounts of mud that ran off into the ocean, smothering and killing coral.
flood control river locks
Heavy Rain in Niigata and Fukushima in July 2011
In July 2011, A 67-year-old man was found dead and five people were missing 30 as torrential rains hammered Niigata and Fukushima prefectures, the Asahi Shimbun reported. Niigata Prefectural Police Department said the man had apparently been driving home from a hospital on the night of July 29, when his car was swept into a river in Tokamachi. His body was found the next morning about 1.8 kilometers downstream. [Source: Asahi Shimun, July 31, 2011]
Four others were missing in Niigata Prefecture, including a 63-year-old man who is believed to have drowned while he was stacking sandbags along a river bank in Ojiya. Embankments broke on the Aburumagawa and Hanegawa rivers in Uonuma, the Ikarashigawa river in Sanjo, the Chagogawa river in Ojiya and the Makikawa river in Gosen. The Uonogawa and Kariyatagawa rivers in Nagaoka also broke their banks.
About 365,000 people in 15 municipalities, including Sanjo, Niigata and Nagaoka, were advised to evacuate. There was also extensive damage in Fukushima Prefecture, with communities left isolated by landslides and damaged bridges. A total of 711.5 millimeters of rain was recorded at Tadamimachi in Fukushima Prefecture.
On July 29, the rainfall set all-time records, with an hourly precipitation of up to 121.0 millimeters recorded in some locations. According to the Meteorological Agency, the precipitation was heavier than rains that hit the two prefectures in 2004, killing 15. Hourly rainfall on July 29 hit 93.5 millimeters in Kamo, Niigata Prefecture, 121.0 millimeters in Tokamachi, Niigata Prefecture, and 69.5 millimeters in Tadami, Fukushima Prefecture, setting record highs at those stations. July 30 brought more record downpours in Niigata Prefecture, with 89.5 millimeters recorded in Minami-Uonuma, 70.0 millimeters in Uonuma, 68.0 millimeters in Nagaoka and 58.0 millimeters in Joetsu.
A 65-year-old farmer, whose house and rice paddies are near to the broken right bank of the Ikarashigawa river in Sanjo, told the Asahi Shimbun,"When the flood hit (seven years ago), it rained very hard but the sky went clear at once," he said. "This time around, it's been raining persistently for two days on end. I'm worried about my home. My paddies are probably spoiled."
Heavy Rain in 2012, Twenty-five Dead in Kyushu
In July 2012, the Yomiuri Shimbun reported: “Torrential rains caused by a seasonal rain front have brought death and destruction to the nation, mainly in western Japan.A number of people have been killed or are missing. The victims were crushed in their homes by mudslides or swept away by rain-swollen rivers. In the past month, there have been over 350 reported landslides. In Matsue, a mudslide on the slope behind a private house caused two huge rocks, each measuring four meters in diameter, to strike the building, killing two residents. In Yaotsucho, Gifu Prefecture, a mudslide crushed a private house, killing three residents. On July 5 this year, an intense rainfall of 107 millimeters per hour was recorded in Tokyo's Itabashi Ward.[Source: Yomiuri Shimbun, July 17, 2010]
In July 2011, 25 people were confirmed dead as a result of torrential rains, flooding, landslides and mudslides caused by a strong seasonal rain front in Kumamoto, Fukuoka and Oita Prefectures in northern Kyushu, according to police. Seven people were missing. More than 240,000 people were advised to evacuate their homes. [Source: Yomiuri Shimbun, July 13, 14, 15, 16, 2012]
“In Yame, Fukuoka Prefecture, Yame Police Station confirmed the death of Katsutoshi Matsumoto, a 70-year-old farmer. Matsumoto was engulfed in a mudslide and was found in cardio-respiratory arrest. In the city of Yanagawa, Masayuki Kawaryu, a 28-year-old unemployed man from Miyama in the prefecture, was found near a car that fell into a ditch. According to Yanagawa Police Station, the ditch was used for farming and measured about 24 meters wide and three meters deep.He was later confirmed to have drowned. Earlier a passerby witnessed the car falling into the ditch. But the car immediately sank in the water and rescuers could not find it. that day. In Taketa, Oita Prefecture, a 74-year-old man died in a flooded river. [Ibid]
“In Oita Prefecture, the Yamakunigawa river in Nakatsu and the Kagetsugawa river in Hita overflowed. In Hita, an evacuation advisory was given to 33,700 people in 12,000 households. Oita Gov. Katsusada Hirose requested Self-Defense Forces personnel be dispatched for disaster-relief operations. In Fukuoka Prefecture, 190,000 members of 66,000 households across a wide area were advised to evacuate. A similar advisory was issued to about 16,500 people from 6,000 households in the city of Saga. [Ibid]
“In northern Kyushu, rainfall of 90 millimeters in one hour was registered in the town of Soeda, Fukuoka Prefecture, at about 5:30 a.m. and 85 millimeters was recorded in Hita at about 7:15 a.m Record-setting hourly rainfalls of 110 millimeters were recorded near Yame and Chikugo in Fukuoka Prefecture around 9:30 a.m. In the three days up to 11:20 a.m., the cumulative rainfall was about 780 millimeters in Aso, Kumamoto Prefecture, 650 millimeters in Yame and 600 millimeters in Hita. [Ibid]
“In Aso, Kumamoto Prefecture, 17 people have been found dead, while five others are still missing. In nearby Minami-Aso, a 26-year-old man was found dead in his collapsed house. An 81-year-old woman had not returned to an evacuation center after leaving for her home in Takamori, Kumamoto Prefecture. Jiji Press reported: “According to the Japanese Meteorological agency, 108 millimeters of rainfall per hour was recorded shortly before 6 a.m. on July 12 in the city of Aso, Kumamoto Prefecture, which saw a cumulative rainfall of 507.5 millimeters in the 24 hours to noon. According to the Kumamoto prefectural police headquarters, many houses collapsed due to landslides in Aso. Nine people were confirmed dead in the city. In Aso and the neighboring village of Minami-Aso, the whereabouts of at least 10 people were unknown. [Ibid]
Strong Winds and Tornadoes in Japan
Tornadoes are rare in Japan but they do occur at a rate of 20 or so a year, compared to 800 a year in the United States. Most tornadoes in Japan are relatively weak. On a scale of F1 (weakest) to F5 (strongest) only two F3s have ever been recorded: in Toyohashi in Aichi in 1999 and Mobara in Chiba in 1990. No F4s or F5s have ever been recorded.
In November 2006 a tornado struck the town of Saromacho in Hokkaido, killing nine people and injuring 21. Producing a funnel cloud and 200kph winds, it ripped off roofs, leveled rows of trees, toppled power poles, flipped cars and broke windows along a 200-meter-wide, one-kilometer trail, with most of the damage occurring in a 100 square meters area near a main road. Most of the dead were construction workers gathered for a meeting in a lightweight prefabricated office that was blown apart by the tornado.
The tornado occurred during a spell of unusually warm weather when a mass of warm air collided with a mass of cold air. A tornado had been reported in that area before. Debris from the destroyed prefabricated building were found 1.2 kilometers from the site. Even so the tornado was regarded as only an F2.
In September 2006, a tornado kicked up by Typhoon 13 struck the city of Nobeoka in Miyazaki Prefecture, killing three people and injuring 151. It destroyed roofs, broke windows in homes, schools and other buildings in a path about six kilometers long and 100 meters to 200 meters wide.
In June 2004, tornado-like winds that reached speeds 250 kph in Saga Prefecture damaged 330 buildings, primarily by ripping off roofs, overturning vehicles and bringing down power lines.
In October 2009, tornados battered towns in Aomori and Akita Prefectures. One man was injured. Several houses were damaged.
Strong winds sometimes shut down plane and rail service. In April 2010, intense winds caused the cancellation of 92 flights at Haneda Airport and injured 29. Winds of 118 kph hour were recorded in Tokyo. Haneda reported a wind gust of 105 kph. Strong winds a month earlier caused by a strong low pressure system off Tokyo , hurt 140 and uprooted a famous 800-year-old sacred gingko tree at Hachmangu shrine in Kamakura, Kanagawa Prefecture. Most of those hurt received minor injuries when they fell down or were in vehicles pushed by the winds.
See Train Accident
Image Sources: 1) Aizu city site 2) Snow Japan 3) Japan Zone 4) 7) Ray Kinnane 5) LIbrary of Congress, 6) Earthquake Image Archives M. Yoshimine, Tokyo Metropolitan University
Text Sources: New York Times, Washington Post, Los Angeles Times, Daily Yomiuri, Times of London, Japan National Tourist Organization (JNTO), National Geographic, The New Yorker, Time, Newsweek, Reuters, AP, Lonely Planet Guides, Compton’s Encyclopedia and various books and other publications.
© 2009 Jeffrey Hays
Last updated January 2013