Considerations on hazard prediction method with rainfall index in the case of 2014 Hiroshima landslide disaster

Abstract

On 20th August, 2014, a series of slope failures and debris flows occurred around city of Hiroshima, Japan. The debris flows took place at 107 valleys and slope failures occurred at almost 59 locations between 3 am to 4 am., costing 74 lives and left 44 injured. This calamity was caused by the 2 hours and more continuing torrential rainfall of more than 80 mm/h intensity, which took place under the squall line formed by a sudden weather change. In this report, the considerations were made on how the present hazard prediction methods with the rainfall index were applied and worked in this disaster. The points to be improved were discussed.

Study on an Evaluation Method of Initiation Probability of Debris Flows During Heavy Rainfall

“…Therefore, this study focuses on the rainfall index ′ 2), 3), 4) , that assesses the risk of a sediment-related disaster caused by heavy rainfall. This index represents a comprehensive assessment of the risk of a debris flow occurrence based on the long-and shortterm effective rainfall.…”

“…Appropriate weighting factors and other parameter settings are considered to vary depending on the topography and geology. In this case, we set the parameters proposed in the previous research based on the actual data from the "6.29 Disaster" (the torrential rain disaster of June 29, 1999, caused by a seasonal rain front) 2) ,3) , 4) . combines a long-term rainfall index and a short-term rainfall index into a single index, which makes it easier to describe how the risk of a debris flow initiation changes over time on a map.…”

“…They also succeeded to achieve a very good match between the prediction and the result of the Hiroshima heavy rainfall disaster of August 2014. Here, the 10-min rainfall data were used to estimate the risk of a sediment-related disaster, where the index reached =250 mm or greater in the affected areas prior to about 3:00 on August 20, when several debris flows began 4) . Table 1 compares the maximum values and times of occurrence of the 72-h half-life effective rainfall, the 1.5-h Table 1 Maximum values of effective rainfall and R' in previous disasters.…”

“…This study aims to explain the characteristics of the Heavy Rain Event of July 2018 and investigate the method of assessing the probability of debris flow initiation through the rain index ' 2), 3), 4) , using topographic and rainfall distribution data.…”