1. Heavy rain disaster
  2. Intensity and characteristics of rain
  3. To prepare before heavy rain comes
  • Safety measures
  • Preparation of emergency supplies
  • Preparation of emergency survival bags
  • Confirmation of the hazard maps
  1. What to do when heavy rain starts to fall
  • What to pay attention to when heavy rain is falling
  • Confirmation of the distribution of risks (landslides, floods from inland waters and floods from rivers)
  • Confirmation of the alert level
  1. Predictors of Sediment Disasters
  • Cliff collapse
  • Landslide
  • Debris flow
  1. Disaster Emergency Message Service

1.Heavy rain disaster

In Japan, it sometimes rains heavily according to the seasons.
Between May and July during the change from spring to summer, a seasonal (Baiu) front stays stationary, and between September and October during the change from summer to autumn, an autumn rain front stays. These bring heavy rain.
In summer, heavy rain is caused by typhoons. Also, heavy rain concentrated in specific regions can occur.
Sustained rain and short-term heavy rain in the same area can cause flooding of rivers, debris flows, landslides, and cliff collapse.
During storm winds, high waves, or storm surges, it may become an even bigger disaster. 

In addition to natural disasters, heavy rain can also cause inundation, power outages and water outages, which can severely affect lifelines. Roads may be blocked, railroads may be suspended and other transportation problems may occur, so extreme caution should be exercised when a typhoon is approaching.

List of heavy rain damage in 2019
DateRegionWeather ConditionsDisaster
Oct.24-26,2019The area centered on Chiba and Fukushima prefecturesHeavy rain caused by low pressure and the 21th typhoon of the seasonOccurrence of sediment disasters, inundation damages and flooding of riversHuman and residential damage Damage to lifeline such as power and water outagesTraffic hindrance such as suspended operation of train
Aug.26-29, 2019The area centered on the north area of KyushuHeavy rain caused by the frontRecord heavy rainsOccurrence of flooding of rivers, inundation damages and sediment disastersHuman, residential, and farmland damagesDamage to lifeline such as power and water outagesTraffic hindrance such as suspended operation of trains

2.Degree and type of rain

To minimize the damage caused by heavy rain, it is important to check the expected amount of rainfall.
According to Japan Meteorological Agency (JMA), the intensity and characteristics of rain can be classified as the following.

Intensity and characteristics of rain (Source: JMA)

Precipitation per 1 hour(mm)Forecast TermImage that people receiveImpact on peopleIndoor(Assuming wooden)Outdoor ConditionWhen Driving a Car
10 to less than 20Moderate heavy rainLashing rainWet legs with water which splashes from groundDifficulty listening to a conversation due to sounds of rainPuddle all over the ground水たまりのイラスト 
20 to less than30Heavy rainPouring rainGetting wet even with an umbrella 雨と傘のイラストNearly half of people notice the rain while sleepingVisibility is poor even while using wiper車のワイパーのイラスト
30 to less than50Very Heavy rainLike flipping a bucket upside downA road becomes like a streamWhen driving at high speed, the brakes doesn’t work due to water film between wheels and road surface (hydroplaning phenomenon)
50 to less than80Extremely Heavy rainLike falls
(thundering rain continues)
An umbrella become uselessWhitish all around with spray and poor visibilityDriving a car is dangerous
More over 80TorrentialOppressing feeling with difficulty breathing. Feeling fear.

3.To prepare before heavy rain falls

To minimize damages caused by heavy rain, it is important to take precautions beforehand.
Pay attention to precipitation predicted by JMA and be prepared as follows.

Even if predicted precipitation is low, when it has rained heavily already, you should be more cautious because sediment disasters and flooding of rivers can easily happen!

  1. Safety measures
    Before heavy rain falls, take enough precautions both indoors and outdoors.
  • Windows and shutters should be tightly closed and locked, and reinforced if necessary.
  • Gutters and drainage pipes should be cleaned and well drained.

This is because when it rains heavily, the water may not run well and can cause overflow! 

  • Be prepared to secure drinking water and fill up your bathtub with water in case the water supply is cut off.
    The water in the bath can be used for the toilet.
  1. Preparation of emergency supplies
    In case of an emergency, check where the following items are located in your home. If needed, procure them.

✔ Flashlight
✔ Portable radio set(battery type) 
✔ First-aid medicines
✔ Clothes
✔ Foods and beverages for emergencies
✔ Portable stove
✔ Valuables

  1. Preparation of emergency survival bags
    In order to be able to evacuate whenever you need, prepare emergency supplies in a backpack or other bags so that your hands are free. 
□ Backpack
Food items□ Beverages□ Foods for emergencies such as soda crackers□ Preserved foods and Canned foods□ Baby goods such as powdered milk and a baby bottle
Daily necessities□ Knife ・ can opener□ Pan ・ water bottle□ Flashlight□ Portable radio set (battery type)□ Batteries□ Rope□ Matches or lighters□ Disposable body warmer□ Papers such as tissues□ Writing materials□ Trash bags
Medicinal products□ First-aid medicines□ Household medicines□ Masks□ Antiseptic available□ Thermometer□ Disposable diapers□ Sanitary itemsValuables, Money□ Cash (including small change)□ Bankbook□ Personal seals□ Health insurance card□ Identification card
Clothes□ Thermal underwears□ Towels□ Sleeping bag□ Rain gear□ Cotton work gloves□ ShoesOthers□Disaster hood helmet非常用持ち出し袋の確認のイラスト□ Spare glasses□ Maps
  • During a disaster, masks, disinfectants and thermometers are in short supply. If possible, prepare them yourselves.
  • In addition to those listed above, you should also check where to evacuate and the route to the evacuation site.
  1. Confirmation of the hazard maps

Before heavy rain falls, it is important to understand the disaster risks in your area.
Hazard maps can help you understand the risk of disasters in your area.
You should check the risk areas with your family in advance, because they can be used to help you consider your evacuation route and how to get to the evacuation site.

Hazard maps are available at your local government office or on the hazard map web portal created by the Ministry of Land, Infrastructure, Transport and Tourism (MLIT). 

『Hazard map portal site~Check the disaster risk around you~』
ContentsBy selecting the area in which you are located, you can find out the risks of natural disasters around you at a single glance.You can use this web portal for the following purposes:Consideration of evacuation routes and methods.Consideration of disaster risks check in the vicinity of your homeConsideration of measures against floodingConsideration of measures against an earthquake
『Wagamachi Hazard map』
ContentsYou can search for Hazard Maps created by cities, towns, and villages across  Japan by map or disaster type. Please see the information listed below.Flood Hazard Map Inland Water Hazard Map Storm Surge Hazard Map Volcanic Hazard Map Tsunami Hazard Map Landslide Hazard Map Reservoir Hazard MapSeismic Damage (Strength of the earthquake’s activity and size) map
『Kasaneru hazard map』
ContentsDisaster risk information that helps in disaster prevention can be freely displayed over maps and photos.The following information is available:Flood inundation hazard areas: Areas of potential inundation due to river flooding and the depth of the water.Potentially flooded roads : Areas where heavy rains may cause flooding and submerged vehicles or the cause of other serious accidents (e.g., underpasses).Emergency transportation roads: Important roads that must be secured for emergency vehicles traffic for rescue, evacuation, supplies, and other emergency operations.Advanced traffic regulation sections: Sections where roadblocks and other restrictions are enforced before a disaster occurs, based on the standards established for regulating areas at risk of landslides and rockfalls due to heavy rainfall and other factors. In addition, you can check the following information:Reservoir flooding hazardous areas Tsunami hazardous areas Sediment disaster-prone areas and sediment disaster hazard areasPriority snow removal sectionAerial photographs from the past to the presentLand Condition map Land Condition map for coastal sea areasLandform Classification Map for flood controlLow Marshy Areas of the Meiji Period MapActive Fault MapBasic Volcanic Map and Volcanic Land Conditions MapColor Elevation Map Color Elevation Map that you can create yourselfLarge Fill Development Site

4.What to do when heavy rain is falling

When heavy rain starts to fall, stay in a safe place until the rain stops by checking the latest weather information on the TV, Internet, or radio.

  1. What to do when heavy rain is falling
    If heavy rain falls, please pay attention to the following points.
  • Do not go outside
    Heavy rain may cause the roads to flood and become as deep and treacherous as a river. It is very dangerous to walk on these roads as you can easily fall down into the water or fall into a manhole with the lid off.
  • Do not go out at night
    Visibility is even worse at night and the danger level increases, so avoid evacuating at night. If there is a possibility that you may need to evacuate at night, please consider the following precautions. Even if you think the rain and winds are not that strong yet, you should consider moving while it’s still light outside.
  • Keep away from rivers
    Even if it is not raining in your area, heavy rains may suddenly occur, and the volume of water in the river may increase rapidly heading upstream.
  • Keep away from the shore

High tides and storm surges can occur which is very dangerous.

  • Keep away from mountains and cliffs
    Heavy rains from typhoons can lead to cliff collapse.
    If your home is on the side of a mountain, stay in a room on the upper floor, far from the mountain.

Avoid any other activities that may be considered dangerous.
Also, don’t let your guard down even if the rain stops.
The ground contains a lot of rainwater which makes it prone to landslides.

  1. Confirmation of the distribution of risks (landslides, floods from inland waters and floors from rivers)
    You can check the distribution of risks of landslides, floods from inland waters, and floods from rivers on the JMA website.
    Check to see if there is any risk of potential disasters in your area at this time.

Extreme caution is required in certain parts of the hazard distribution, especially those marked in dark purple.
Dark purple indicates the highest risk, indicating a serious disaster is likely to occur.

The circumstances of the Onogawa River in Hita City, Oita Prefecture (upper part) and the “Distribution of flood warning risks” (lower part). Black circles indicate the locations where the photographs were taken.
(Information from Government Information Online; photo courtesy of staff members of Hita City, Oita Prefecture; images courtesy of the Japan Meteorological Agency)

Also, don’t get complacent even if you think it’s still in the red or yellow stage of the degree of the risk, since you still should be careful.
As you can see from the photos, the impact of the rain has changed faster than you could imagine. For example, the light purple stage of the river increased to the dark purple level in 30 minutes.
Therefore, if you live in a landslide warning area or an area where there is a risk of river flooding, you should evacuate as soon as possible.
In particular, if it is already raining heavily and more rain is expected, you should evacuate immediately.

Regardless of the risk distribution, if your local government issues an evacuation advisory, you should evacuate to a safe place as soon as possible.

  1. Pay attention to the alert level
    Check the circumstances in your area based on the information released by the Japan Meteorological Agency when necessary.
    You should pay particular attention to the timing of your evacuation and check your evacuation behavior on your hazard map on a daily basis.

✔ There are 5 levels of warning. The elderly, disabled, infants, and toddlers should evacuate from dangerous areas at Level 3 and everyone else should evacuate at Level 4
Alert Level 5 are circumstances where a disaster has already occurred!

Alert levelActions Residents Should TakeInformation on the municipalities based on the Japan Meteorological AgencyWeather Information
Information on RainInformation on Storm SurgeInformation on Risk DistributionFlood Information
1Improving Disaster PreparednessEarly Advisory Information(Possibility of a warning)   A few days to about a day before the heavy rain
Half a day to several hours before the heavy rain 

An hour or two before the heavy rain

Heavy rain that falls once every few decades
2View the hazard map and confirm the evacuation activitiesHeavy rain advisoryFlood advisoryStorm Surge AdvisoryAdvisory
(Possibility of an advisory)
Flood Advisory Information
Advisory likely to switch to heavy rain warning
3If you live in a hazardous area such as the sediment disaster warning areas or along a river where there is a risk of rapid water level rising, start evacuating as soon as you are ready to evacuate. The elderly, disabled, infants, and toddlers should evacuate immediately.Heavy rain warning※1)
Flood warning
Advisory likely to switch to storm surge warningwarning
(Possibility of a warning)
Flood Warning Information
4Evacuate immediately
・Immediately evacuate to a safe place outside the danger area
Sediment Incident Alert InformationStorm Surge Warning(※2)Storm Surge Emergency WarningHigh RiskFlood Risk Information
Complete the evacuation
・Evacuation may already be difficult due to road flooding or landslides and should be completed before this situation occurs
Extreme Risk
5If you are not yet evacuated from dangerous areas, take the best possible action to save your life.・When a heavy rainfall warning is announced, you must consider the fact that there is an urgent situation that increases the risk of a disaster even in places that are not considered to be at risk Heavy Rain Emergency Warning  Flood Occurrence  Information
(※1)In case a heavy rain warning (landslide) is issued during the night or early the next morning, you should prepare for evacuation and the elderly, disabled, infants, and toddlers should begin to evacuate  (Alert Level 3).
(※2)An advisory that is likely to switch to a storm surge alert when a strong wind alert has been issued is equivalent to an evacuation advisory (Alert level 4)
This is a re-edited version of a table prepared by the Japan Meteorological Agency with reference to the “Guidelines for Evacuation Advisories” (the Cabinet Office, 2017).(https://www.jma.go.jp/jma/kishou/know/bosai/images/arasute_5.png
  1. Decide whether you should evacuate
    In case of deciding whether or not to evacuate as a typhoon approaches, you can refer to the decision flowchart and alert levels issued by the Cabinet Office.
  • Use the evacuation decision flowchart
    Please refer to the following flowchart to determine evacuation due to a typhoon or heavy rainfall.

「The Evacuation Decision Flowchart」(Source: The Disaster Prevention Information page of the Cabinet Office)

  • Decide by the alert level
    If the Alert level 3 or 4 is issued in your area, you should evacuate to a safe place as soon as possible.
    Evacuation advisories are issued by your municipality, not the Japan Meteorological Agency.

When municipalities transfer evacuation advisories, they will announce the information as follows.

  • Emergency broadcast, Emergency broadcast, Alert Level 4!Start evacuation. 
    Emergency broadcast, Emergency broadcast, Alert Level 4! Start     evacuation.  
  • This is XX City. Alert level 4 for floods, an evacuation advisory has been issued in the XX area.
  • The water level of the XX river has reached the level of possible flooding.
  • All residents in the XX area should evacuate immediately from the dangerous area.
  • If it is not safe to evacuate to an evacuation site, please evacuate to a nearby safe place or take refuge indoors in a high place.

(Source: The Cabinet Office (in charge of disaster prevention) and the Fire Department)

✔ What is important here is the awareness that you should “save your own life”.

If you feel that you are in danger, even without instructions or warnings from your municipality, evacuate immediately to a safe place. 

✔ Also, Alert Level 5 is a situation where a disaster has already occurred! 
At this level, even moving to an evacuation shelter can be dangerous.
Assess the situation calmly and do the best you can to save your life.

It is also important to talk to your neighbors and cooperate with each other when you evacuate.

5.Predictors of Sediment Disasters

” Sediment disasters” are one of the most common disasters to watch out for when it rains heavily.
There are many mountains with steep slopes in Japan, typhoons, and heavy rain can cause debris flow, cliff collapse, and landslides.

To avoid such disasters, it is important to understand the risks of natural disasters around you using hazard maps, and to evacuate to a safe place as soon as you notice the signs of disasters.

Even after the rain stops, localized torrential rains, and prolonged periods of rain can be dangerous due to the increased risk of landslides. Watch out for them.

  1. Cliff Collapse
    Cliff collapse is the sudden collapse of a slope, close to the ground, as a result of rain inundation or an earthquake.
    If a cliff collapse occurs near homes, people may be unable to escape and may lose their lives.

Before a cliff collapse occurs, the following precursory phenomena may be seen.

  • A crack develops in the cliff
  • Pebbles begin to fall
  • Water gushes from the cliff
  • Tap water stops or becomes muddy
  • The earth rumbles 
  1. Landslide
    This is a phenomenon in which water in the ground and gravity causes part or all of a slope to move downward slowly.
    Since the amount of soil being moved is significant, the damage can be very large.

Before a landslide occurs, the following precursory phenomena may be observed

  • Cracks or crevices from in of the ground
  • Water gushes from cliffs and slopes 
  • The water in wells and streams becomes muddy
  • The earth and mountain rumbles
  • The trees will lean
  • Cracks and unusual bulges in the ground occur
  1. Debris flow
    This is a phenomenon where it rains for a long period of time or a torrential downpour pushes stones and sediment from the riverbed or hillside downstream in one fell swoop.
    As sediment flows downstream at speeds of 20 to 40 km/h, it can devastate homes and fields in an instant.

Before a debris flow occurs, the following precursory phenomena may be seen:

  • The mountain rumbles 
  • The water in the river suddenly becomes muddy and driftwood begins to mix 
  • It smells like rotten dirt 
  • The water level of the river keeps dropping, even though the continues 
  • Hear the cracking of trees and the clashing of rocks

If you notice any of these warning signs, evacuate to a safe place without waiting for an evacuation orders or advisories from your municipality. 

6.Disaster Emergency Message Service

When a major disaster occurs, such as a typhoon, it can be difficult to get through to the affected areas due to the rush of calls confirming the safety of family members and acquaintances.
For this reason, telecommunication carriers provide “Disaster Message Services” to help people confirm their safety and evacuation locations while avoiding communication congestion. 

Disaster Emergency Message Dial(171)
Service DetailsIn the event of a disaster, voice messages such as safety information are registered to a phone number. The person with who has the phone number can play and check the registered voice messages. 
Language SupportedJapanese
How to useDial 171Dial 1 for recording and 2 for playback in accordance with the guidance.You can also record and play back with your PIN here.Follow the guidance and dial the phone number of the person you want to contact.For phone numbers that begin with an area code, such as 03, dial starting with the area code.Record and play back the message.
Available PhonesSubscribed telephones (touch-tone line and dial line) Public telephones ISDNMobile phones・PHSIP phone✔ Registration and replay of the message must be made to the phone number of the person in the affected area. For this reason, phone numbers that begin with an area code such as 03, mobile phone/PHS phone numbers, and IP phone numbers are included. 
NotesThe recording time per message is limited to 30 seconds. You can register up to 20 messages per phone number.If the number of stored messages exceeds the limit, the old messages will be deleted.
Reference LinksYou can check the details of the Disaster Message Service, Dial at NTT’s (East and West), service operator. NTT http://www.ntt.co.jp/saitai/171.html  NTT East http://www.ntt-east.co.jp/saigai/voice171/  NTT West https://www.ntt-west.co.jp/dengon/  
Disaster Message Board
Service DetailsPeople in the affected areas can register messages by text using the internet connection function of their mobile phones or PHS, and then check the messages from all over Japan based on their mobile phone or PHS number. 
Language SupportedJapanese, English
How to useHow to register messagesAccess the Disaster Message Board from a mobile phone or PHS Select “Registration” for “Disaster Message Board”.Registration is only accessible from mobile phones and PHS in the affected area.Choose a comment about your current state from options such as “I’m fine.” and enter a comment of up to 100 words optionally.You can use multiple selections of comments to indicate the current status, or use only free commentsFinally, press “Register”. How to check the messages (also possible via PC)Access the Disaster Message BoardNTT docomo http://dengon.docomo.ne.jp/top.cgi KDDI(au)http://dengon.ezweb.ne.jp/   SoftBank/Y!mobile http://dengon.softbank.ne.jp/  Select “Confirmation” for “Disaster Message Board”.Enter the mobile phone/PHS number of the person whose safety you want to check and press “Search”.From the list of messages displayed, select the message you want to check.
NotesYou can register up to 10 messages per phone number.Messages exceeding the number of messages will be overwritten from the oldest ones.Messages are stored until the disaster message board for one disaster ends.
Reference LinksFor more information on Disaster Message Boards, please check the pages of each company.NTT docomo Disaster Message Board Servicehttps://www.nttdocomo.co.jp/info/disaster/disaster_board/index.html KDDI(au)Disaster Message Board Servicehttps://www.au.com/mobile/anti-disaster/saigai-dengon/  SoftBank  Disaster Message Board/Disaster Voice Messaging Servicehttps://www.softbank.jp/mobile/service/dengon/ Y!mobile Disaster Message Board Service https://www.ymobile.jp/service/dengon/  
Disaster Message Board(WEB171)
Service DetailsYou can register and check messages regarding safety information by entering the phone number of your landline phone, mobile phone, or PHS from your PC or smartphone. 
Language SupportedJapanese, English, Korean, and Chinese languages
How to useAccess the Disaster Message Board (web171)URL:https://www.web171.jp/Enter the landline or mobile phone number of the person you want to contact.Register or confirm the message.Users can also be limited by setting it up in advance.Messages can be registered as text, with a maximum of 100 double-byte characters per message.
NotesYou can register up to 20 messages per phone number.Registered messages are stored for up to six months until the end of the service.
Reference LinksFor more information on the Disaster Message Board (web171), please refer to the following NTT (East and West) pages.NTT East http://www.ntt-east.co.jp/saigai/web171/ NTT West https://www.ntt-west.co.jp/dengon/web171/  
Disaster Voice Messaging Service
Service DetailsA dedicated application is installed on a smartphone or other device and voice messages are sent. Voice messages can also be sent between carriers that provided this service.
Language SupportedJapanese, English
How to useEnter the following keywords in Google Play or Apple Store to search for the app.NTT docomo:「Disaster Kit」KDDI(au):「au Measures in Times of Disaster or Emergency 」SoftBank:「Disaster Message Board」Y!mobile:「Disaster Message Board」Download and install the dedicated application.Start the application and follow the instructions.
NotesRegistration time is limited to 30 seconds per message.You can register up to 20 messages per phone number.Registered messages are deleted when the recipient downloads them. Even if not downloaded, the messages will be deleted after a certain period of time.
Reference LinksFor more information on the Disaster Voice Messaging Service, please refer to the pages of the operating mobile phone companies.NTT docomo https://www.nttdocomo.co.jp/info/disaster/disaster_voice/ KDDI(au) https://www.au.com/mobile/anti-disaster/onsei-otodoke/SoftBank https://mb.softbank.jp/mb/service/dengon/about/voice/Y!mobile https://www.ymobile.jp/service/dengon_voice/  

・The above content is based on the following information. If there are any changes in the references, please be aware that it may take some time for the changes to be reflected on this site. 


・『Preparing for heavy rain and typhoons』(pdf), ​Japan Meteorological Agency(JMA)

・「Intensity and characteristics of rain」, JMA

・「Examples of Meteorological Events Causing Disasters (1989–this(current) year)」,​JMA

・「preparedness yourself for a disaster」,JMA

・「What is a superimposed hazard map? What is our town hazard map? Easily investigate the disaster risk」 (pdf), Hazard Map Portal site, MLIT

・「Pay attention to weather information for heavy rain and typhoons and take disaster prevention and evacuation measures as soon as possible」,Public Relations Office of the Government of Japan

・「Three points to protect yourself from landslide disasters!」,Public Relations Office of the Government of Japan

・「Revision of the guidelines for evacuation advisories (March 29, 2019)」,​Disaster Prevention Information Page, Cabinet Office

・「Disaster Message Service」,Ministry of Internal Affairs and Communications (MIC)