realtime forecasting of shallow landslides using radar-derived rainfall ryohei misumi, masayuki...
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REALTIME FORECASTING OF SHALLOW LANDSLIDES USING RADAR-DERIVED RAINFALL
Ryohei Misumi, Masayuki Maki, Koyuru Iwanami,
Ken-ichi Maruyama and Sang-Goon Park
National Research Institute for Earth Science and Disaster Prevention, Japan
By
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Shallow landslide at Izumozaki-town, Niigata Prefecture on 13 July 2004
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Outline
X-band polarimetric radar
Distributed rainfall-runoff model
Real-time forecast of landslides
Soil water
Rainfall estimation in high accuracy and resolution
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WeightBed rock
Soil layer
Slip surface
Sliding force
Shear resistance
Normal situation
What is shallow landslide ?
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Bed rock
Soil layer
Saturated Zone
Soil particles
Water During heavy rainfall
Increase of pore pressure
Decrease of normal stress
Rain
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Estimation of rainfall intensity using the specific differential phase (KDP)
not affected by rain attenuation
immune to beam blockage
less sensitive to beam filling and drop size distribution
++
Z KDP
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Disdrometer
+
R-KDP
R-Z
R-Z (corrected)
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Catchment50m grid
Rainfall
Distributed rainfall-runoff model
Evaporation
Infiltration
Direct runoff
Base flow
Maximum storage capac
ity
SmaxWater
storage
S
50m grids
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tan
'tan)])((1[
cossin
' w
z
h
z
cF
γγ
γ
Infinite slope stability analysis
F: Factor of safety
γ, c', Φ': Soil properties
γw: Density of water
h: Level of groundwater
z: Depth of soil
β: Inclination of slope
maxS
S
z
h
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80km
Tsurumi river basin
MP-X radar
Real-time evaluation
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Meso-β scale depression on 9 July 2005
22:59
Rainfall rate
Water storage
Predicted landslides
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Meso-β scale depression on 9 July 2005
23:29
Rainfall rate
Water storage
Predicted landslides
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Meso-β scale depression on 9 July 2005
23:53
Rainfall rate
Water storage
Predicted landslides
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3 km
Actual landslide
Predicted grid
Landslide on 9 July 2005
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Evaluation with past events
Upper Abukuma River basin (151.07km2)
Rainfall event in August 1998
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0 4321 5
02JST on 27 August
(2 hours before severe landslides)
Distance (km)
Dis
tanc
e (k
m)
Slope failure
Predicted grids
Welfare facility
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Predicted factor of safety (F) and occurrence of landslides
Factor of safety
Occur Not occur
F < 1 205 grids 1809 grids
F > 1 56 grids 5318 grids
Correct forecasts: 74.8 %
False alarm ratio: 89.8 %
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Conclusions
An accurate forecast of shallow landslides is still difficult.
Increase of landslide potential in a few-km scale may be predictable using rainfall observation with the X-band polarimetric radar (lead time is about 2 hours).
The lead time would be greatly extended if a reliable QPF is available.