Glossary
10-min rainfall
The amount of rainfall in the past 10 minutes up to the last
ten minutes of each hour (1:00, 1:10, 1:20, 1:30, etc.) before the
displayed time
1-hour rainfall
The amount of rainfall in the past 1 hour up to the hour (1:00,
2:00, 3:00, etc.) immediately before the displayed time
1-min rainfall
The amount of rainfall in the past 1 minute up to the displayed
time
24-hour rainfall
The amount of rainfall in the past 24 hours up to the hour
(1:00, 2:00, 3:00, etc.) immediately before the displayed time
Accumulated rainfall
Rainfall from the start of the rain until the displayed time
When there is no rainfall for 6 hours, the accumulated rainfall is
reset, and after that when rainfall is detected, it will be
considered a new rain (start of the rain).
Alarm
Information to be announced by the Japan Meteorological Agency
when a serious disaster may occur due to heavy rain or strong winds
Displayed water level
Approximation of water level of general rivers
- Caution
40-60% of the height of the revetment
depending on the width of the river
- Alert
70-90% of the height of the revetment depending on the width of the river
Flood alarm river
- A river for which water level information is provided to the Flood Defense for the purpose of carrying out flood prevention activities when there is a risk of flooding.
- Among the rivers managed by the Tokyo Metropolitan Government, those in this category are Sakai River, Tsurumi River, Onda River, and Shinkoji River.
Flood alert information
- Information regarding flood forecast rivers, announced when the water has reached the level which requires evacuation, or when it is projected that the water will reach the flood danger level based on the water level prediction
- Among the flood forecast rivers in Tokyo, only Shiba River and Shin Shiba River are subject to announcement of this information
Flood danger information
- Information regarding flood forecast rivers, announced when it is projected that the water level is going to reach the surface of the levee or revetment, or when the water level has reached the flood danger level and is projected to rise higher
- Information regarding water level well-known rivers, announced when the water level has reached the flood danger level
Flood danger water level
Water level that poses a risk of flooding which results in considerable damages such as flooded houses and buildings
Flood forecast river
- A river for which the Japan Meteorological Agency and the Tokyo Metropolitan Government jointly provide citizens with information regarding risks of flooding.
- Among the rivers managed by the Tokyo Metropolitan Government, the Kanda River, Meguro River, Shibuya River, Furukawa River, Nogawa River, Senkawa River, Shiba River, Shin Shiba River, Myoshoji River, and Shakujii River are subject to the forecast.
- For the Kanda River, Meguro River, Shibuya River, Furukawa River, Nogawa River, Senkawa River, and Myoshoji river, only the flood danger information is announced.
Flood inundation information
- Information regarding flood forecast rivers in case flood has occurred
- Among the flood forecast rivers in Tokyo, only Shiba River and Shin Shiba River are subject to announcement of this information
Flood inundation water level
- Water level in the vicinity of the water level observatory which indicates that flood will occur and cause damage to houses and buildings
Flood warning information
- Information regarding flood forecast rivers, announced when the water has reached the flood warning water level and is projected to continue to rise higher
- Among the flood forecast rivers in Tokyo, only Shiba River and Shin Shiba River are subject to announcement of this information
Flood warning water level
Water level at which flood defense organizations are mobilized to prevent flood damage
Hourly maximum rainfall
Maximum rainfall for any hour from the beginning of the rainfall
Hourly maximum rainfall duration
An hour during which a maximum rainfall is recorded
Normal
Water level which does not require special attention for flood prevention activities
Sediment-related disaster alert information
Disaster prevention information jointly announced by the prefectures and the Japan Meteorology Agency so that the heads of municipalities can make judgments on issuing evacuation recommendation and the local citizens can voluntarily evacuate.
Stand-by water level for Flood Defense
Water level in the flood alarm river that each flood defense organization makes preparation for flood defense activities
Warnings
Information to be announced by the Japan Meteorological Agency when a disaster may occur due to heavy rain or strong winds
Water level
Height from the riverbed to water surface at a water level observatory
Water level fluctuation
Rise
A condition in which the water level has risen 1 cm or more compared to a minute ago
No fluctuation
A condition in which the water level has fluctuated less than 1 cm compared to a minute ago
Fall
A condition in which the water level has fallen 1 cm or more compared to a minute ago
Water level from top of the dike
Height from the top of the levee or revetment to the water surface
Water level well-known river
- A river other than ""flood forecast rivers"" for which citizens are provided with information regarding risks of flooding.
- Among the rivers managed by the Tokyo Metropolitan Government, those in this category are Zenpukuji River, Nomigawa River, Tsurumi River, Onda River, Shinkoji River, and Sakai River.
Water level which requires evacuation
Water level which requires special alert regarding the occurrence of disaster caused by the flood