Early-warning systems for natural disasters are important tools for disaster risk reduction and for achieving sustainable development and livelihoods. In 2005, the Japanese government initiated a new nationwide early-warning system for landslides disasters. The main methodology of the system is to set a criterion for occurrences of debris flows and slope failures based on several rainfall indices (60-min cumulative rainfall and soil-water index) in each 5-km grid mesh covering all of Japan. Because many of the records of mass movements are lacking in scientific precision on timing and location, the system applies Radial Basis Function Network methods to set the criterion based primarily on rainfall data recorded as not triggering disasters. Since the end of March 2007, under torrential rainfall conditions, early-warning information has been disseminated as part of weather news using TV, radio, and the Internet. Because of the increasing worldwide recognition of the importance of early-warning systems for natural disaster reduction, the aim of this article is to introduce the new Japanese early-warning system to the international landslide community. In this article, the method, the system, and the result of its application to landslide disasters in 2009 are presented.

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Early-warning systems for natural disasters are important tools for disaster risk reduction. In 2005, the Japanese government initiated a new nationwide early-warning system for landslide disasters. The system uses the RBFN method to set the criterion (Critical Line: CL) primarily based on rainfall data recorded as not triggering disasters. Moreover, after large earthquakes, the thresholds (CL) are scaled down by 20-50%, considering the seismic disturbances in the slopes. In this study, we examined the validity of these ratios by analyzing disasters which occurred during the seven months after the Great East Japan Earthquake. As a result, we found that the use of interim CL improved the landslide capture rate by 18.8%, indicating that the interim standard is effective. The required minimum ratio of scaling down the interim CL is 20-30% in areas affected by more than level 5+ earthquakes without changes of landslide capture rates. The required minimum ratios are expected to reduce false predictions.

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