台風災害の周期性解析と危険度評価

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Periodicity of fluctuations of typhoon disasters in Okinawa is analyzed by the spectral method. Risk against typhoons is also assessed through evaluation of the risk potential for humandisasters.Investigation of historical changes both in typhoon disasters and in coastal and social environments leads to the fact of increase in risk potential near coastal regions to typhoons, storm surges, and tsunami.A new model of spectra for the intermittent time series of disasters and the extreme-value series of climates is developed for extraction of the periods of fluctuations, based on the pulse series analysis. Interrelation between the periods in disasters and climates is clarified. Long-term periodicity of about 9 years exists in the full range 76-83 year time series of typhoon disasters, which is nearly resonant with the 9-11 year period in the full range 42-96 year time series of the number of typhoons, the maximum wind speed, and the maximum instantaneous wind speed. But, in recent 30 years the periods of typhoon disasters have been reduced to the 5.4-7.7 year periods. The 5.4 year period of human disasters is associated with the period of rainfall. On the contrary, the 7.7 year period of the dead is roughly resonant with those of wind speeds and barometric pressure. The fact denotes that the disaster of the dead is chiefly caused by strong winds.A method for risk assessment to typhoon disasters is presented and the usefulness is verified by the real data obtained from retroactive investigation using the newspapers. The method is available for the data obtained on many locations spread widely, and then the details between the number of disasters and meteorological conditions being unknown. Reduction of disasters due to human factors, such as careless action, is important to increase in the potential of disaster prevention. In the method, to properly assess risk, the suitable threshold value of the contribution ratio to typhoon disasters is about the mean value 1/N, where N is the total number of measuring sites.As the results of risk assessment with the threshold value of 1/N, it is clearly seen that the disaster preventive ability in Okinawa became high because of recent development in social bases. However, the extreme-value analysis shows that the typhoon disasters in Okinawa have been occurred by small scale typhoons. Therefore, the disaster preventive ability is still not enough judging from the scale and number of typhoons and the present states of coastal and social environments. Occurrence of human disasters reflects psychological problems, which should be taken into considerations in planning any disaster preventive countermeasures.
琉球大学工学部の論文

著者

筒井茂明
Department of Civil Eng. and Arch., University of the Ryukyus

台風災害の周期性解析と危険度評価

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