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REALTIME FORECASTING OF SHALLOW LANDSLIDES USING RADAR-DERIVED RAINFALL By Ryohei Misumi, Masayuki Maki, Koyuru Iwanami, Ken-ichi Maruyama and Sang-Goon Park National Research Institute for Earth Science and Disaster Prevention, Japan Shallow landslide at Izumozaki-town, Niigata Prefecture on 13 July 2004 Outline Rainfall estimation in high accuracy and resolution X-band polarimetric radar Distributed rainfallrunoff model Real-time forecast of landslides Soil water What is shallow landslide ? Normal situation Shear resistance Soil layer Sliding force Slip surface Weight Bed rock Water Soil particles During heavy rainfall Increase of pore pressure Rain Saturated Zone Soil layer Decrease of normal stress Bed rock 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 ＋ R-KDP R-Z + R-Z (corrected) Disdrometer Distributed rainfall-runoff model 50m grid Catchment Rainfall Evaporation Infiltration Direct runoff 50m grids Water storage Base flow S Maximum storage capacity Smax Infinite slope stability analysis γw h tan ' c' F [1 ( )( )] γz sin cos γ z tan 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 h S z S max Real-time evaluation Tsurumi river basin 80km MP-X radar Meso-β scale depression on 9 July 2005 22:59 Water storage Rainfall rate Predicted landslides Meso-β scale depression on 9 July 2005 23:29 Water storage Rainfall rate Predicted landslides Meso-β scale depression on 9 July 2005 23:53 Water storage Rainfall rate Predicted landslides Landslide on 9 July 2005 Actual landslide Predicted grid 3 km Evaluation with past events Upper Abukuma River basin (151.07km2) Rainfall event in August 1998 02JST on 27 August Slope failure Predicted grids Distance (km) (2 hours before severe landslides) Welfare facility 0 1 2 3 4 Distance (km) 5 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 % 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.