September is a time when we are encouraged to think about disaster preparedness, with many disaster preparedness drills held in communities throughout Japan over late August through September. 1 September was designated Bōsai no Hi (防災の日 / lit. Disaster Prevention Day) in 1960, the date of the Great Kanto Earthquake (関東大震災 / Kantō dai-shinsai) of 1923, and a number of other catastrophic natural disasters have occurred in Japan around this time of year.
Torrential rain and floods have inflicted a great deal of damage around Japan this year, from the Tohoku region to Kyushu, including parts of neighboring Gifu Prefecture. The Tokai region and Nagoya are no strangers to water-related disasters. September 2020 marks 20 years since the Tokai Torrential Rain disaster (東海豪雨 / Tōkai Gōu) and 61 years since the Isewan Typhoon (伊勢湾台風 / Isewan Taifū), both of which inundated parts of Nagoya.
Here we take a look at storm and flood-related disasters, particularly the Isewan Typhoon, and ways you can help yourself to be better prepared for when these kinds of disaster occur.
Storm and Flood-related Disasters
The expression fūsuigai (風水害, lit. wind water disaster) refers to storm and flood-related disasters. In other words, disasters caused by strong wind and rain, such as typhoons (台風, taifū) and heavy rain (大雨 / ōame) or torrential rain (豪雨 / gōu), tornadoes and so on.
What kind of meteorological phenomena cause storm and flood-related disasters?
■Typhoons (台風 / taifū)
A low pressure system that forms over the ocean in tropical areas is called a tropical depression, but when the speed of winds near the center of the low pressure system exceeds 17.2m per second, the depression is classified as a typhoon.
Typhoon strength and damage
The strength of a typhoon is indicated by its maximum wind speed (meters per second). This shows the speed of the wind, by rendering it as the number of meters the wind travels in one second.
■Localized torrential rain (集中豪雨 / shūchū gōu)
When a lot of rain fails in a short time within a small area. Such localized torrential rain can occur from the end of the rainy season (梅雨 / tsuyu) and throughout the typhoon season.
■Tornadoes (竜巻 / tatsumaki)
Updrafts within cumulonimbus clouds cause the rotation of air currents, generating tornadoes. Tornadoes can occur throughout the typhoon season.
Types of storm and flood-related disasters
■Flooding (水害 / suigai)
Floods (洪水/ kōzui) / External inundation (外水氾濫 / gaisui hanran)
Flooding of residential areas, etc. caused by the bursting of a river bank, or a river overflowing due to heavy rain.
Internal inundation (内水氾濫 / naisui hanran)
Flooding which occurs when drains and sewers are not able to cope with the large volume of water suddenly flowing through them due to heavy rain, and overflowing water inundating urban areas.
With the covering of roads in asphalt, the decrease in rice paddies and fields, etc. there is less exposed earth into which rain can be absorbed, and water can build up in urban areas. People near rivers or in low lying areas need to be cautious.
■Storm surge (高潮災害 / takashio saigai)
An extreme rise in the sea level as a typhoon approaches is called a storm surge. The low air pressure of the typhoon draws the sea level upwards, while the strong winds drive the water to surge forward. The Isewan Typhoon was the disaster with the greatest amount of damage caused by a storm surge in Japan (see right). People near the coast need to be cautious.
Storm surge mechanics
① The drawing effect - As atmospheric pressure decreases, the water level is drawn up by the air, causing the sea level to rise. (For every 1 hPa / millibar drop in atmospheric pressure, the sea level is estimated to rise by 1cm)
② The wind effect - Strong winds blowing from the open ocean towards the coast cause the sea to surge at the coast, causing the sea level to rise.
■Sediment-related disasters (土砂災害 / dosha saigai)
Sediment-related disaster refers to such occurrences as debris flows (土石流 / dosekiryū, i.e. a flow of mud, rock, sand, soil and water from mountains and rivers), landslides (地すべり / jisuberi), and slope failures (がけ崩れ / gake kuzure). People near mountains or steep slopes need to be cautious.
The Isewan Typhoon
Making landfall at 18:15 on 26 September, 1959, near Shionomisaki in Kushimoto Town, Wakayama Prefecture, the Isewan Typhoon (Typhoon Vera) traversed the Japanese islands from the Kii Peninsula to the Hokuriku region over 26 and 27 September, causing tremendous damage and casualties over an extensive area. The devastation was the worst inflicted by a typhoon on Japan, with much of the damage concentrated in Aichi and Mie prefectures.
The accompanying storm surge saw the sea level of Nagoya Port swell to 5.31 meters, the highest ever observed in the port. In many places, the surging seawater overran or burst river embankments, inundating the surrounding towns, and remained for up to two months in some parts.
Across Japan, 5,098 people lost their lives or were reported missing; of those, 3,260 were in Aichi, and 1,851 in Nagoya City.
Why were the damage and casualties so extreme?
① The highest ever storm surge and the worst possible path of the typhoon
Areas to the right of a typhoon's path will experience stronger winds. For the Tokai region, the Isewan Typhoon approached on the worst possible path, causing violent winds and a storm surge, the highest recorded in Nagoya Port.
② Urban development in areas at sea level
The elevation of parts of southwestern Nagoya is actually lower than sea level, and many factories and wooden single-story houses had been built in these areas. Wooden structures are weaker and susceptible to water damage, and the single-story dwellings meant that people were unable to protect themselves by evacuating upstairs or to other higher points.
③ Timber from lumberyards carried on the surging current
There were a number of lumberyards from Nagoya Port and along the Horikawa River, where imported timber was kept. At the time of the Isewan Typhoon, the quantity of timber was greater than the capacity of the lumberyards, resulting in timber being stored temporarily in nearby canals and on rafts. The storm surge carried this timber with the sea water inland, destroying houses, river embankments and revetments, and causing a great loss of life.
④ Blackouts hindering the dissemination of information to communities
Blackouts struck Nagoya, preventing residents from receiving vital information on the approach of the typhoon, and evacuation orders.
Help yourself to be prepared
① Things to do day to day
- Keep stormwater drains and inlets clean
- Remove or put away anything around your house that could be blown away
- Keep your valuables and important documents upstairs
- Confirm the location of designated emergency assembly points and designated evacuation shelters, and the route you will take to get there
- Familiarize yourself with the inundation risk around the area where you live and work with the flood hazard map (see below)
- Familiarize yourself with the different levels of evacuation information which could be issued
② Get information
Establish how you will obtain information in a disaster, e.g. via TV or radio, through the emergency speaker system, from the website, e-mail notification service or SNS of the Japan Meteorological Agency or your local government
③ Things to have prepared in case of an emergency
Food, torch, eating utensils, clothing, bedding, valuables, medical supplies, sanitary items, mobile battery, portable toilet, rainwear, etc.
④ Help one another
Value day-to-day interaction with your neighbors, and help one another when an emergency occurs
Flood hazard maps
Flood hazard maps allow residents to view the estimated inundation risk for a particular area, with differing projected depths rendered in different colors.
Maps are in Japanese, but as long as you can read a map and locate your place of residence, work, etc., you can refer to the color key diagram to see the projected depth for that location. The diagram also shows the projected depth compared to a car, a house, and a multi-storey building.
Maps also contain projections for multiple scenarios, for example a river bursting its banks, or inundation due to torrential rain.
See Read the Flood Hazard Map for more information.
Flood hazard maps for each ward can be viewed on the City of Nagoya website.
If you live in a municipality other than Nagoya City, please inquire at your local government office as to how you can view hazard maps for your area.