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Landslide and debris flow in Hiroshima

Hiroshima city was damaged by two landslide and debris

flow events in 1999 and 2014. On 29 June 1999, a severe

storm event (50-200 mm during five days before the event)

caused a landslide and debris flow disaster that killed 32

people and destroyed 101 houses mainly in Hiroshima

Prefecture. At that time we investigated how landslide and

debris flow events took place in terms of rainfall character-

istics and estimated the critical line for the Hiroshima area,

Figure 4: A conceptual explanation of disaster risk,

hazard, exposure and vulnerability (interpretation

for a huge tsunami in Sendai)

Source: Kaoru Takara

Safer place

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Huge tsunami (Hazard)

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Figure 5: Landslide occurrence around

Hiroshima city in June 1999

Source: Ushiyama, Ohido and Takara, 2001

0 50

0

20

40

60

80

100

100

Effective cumulative rainfall (mm)

150 200 250

Hourly rainfall (mm)

The critical line

No landslide

Landslide occurred

Figure 6: Part of the flood hazard map of the Yagi District in Hiroshima

Source: Hiroshima City home page. Note: The red arrow indicates the location of the second photo overleaf

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and

using effective cumulative rainfall and hourly rainfall that

triggered landslides (Figure 5).

Immediately after this event, the Japanese central

Government established the Act on Promotion of Sediment

Disaster Countermeasures for Sediment Disaster Prone Areas,

which encouraged local governments to disseminate infor-

mation about possible sediment disasters caused by heavy

rainfall-induced landslides and debris flows. Figure 6 is a part

of the flood hazard map of the Yagi District in Hiroshima.