都市水害論(5)-明治時代以降の災害(1)-

Abstract

In the 5th report, natural water disasters in the period from the Meiji era to mainly the year of 1965 AD and their changes are investigated in relation to changes in climate as natural abnormal forces and social environment in the period.In the changes in climate brief considerations are made on changes in solar activitities in terms of sunspots and temperature differences on land areas and at sea surface in the northern hemisphere, as well as number of typhoons generated and landed in the Japanese islands.And in the change in social environment in the period, their indexes are taken as rice and iron production rates and their population rates and the Japanese total population. It was considered that there exists a periodicity in their time revolution of which the period is nearly 50 to 60 years as recently stated by Sherman (1985).By use of Saito's chronological table of natural disasters, remarkable water disasters which resulted in human damage were listed for the period from 1700 to 1965 AD in terms of the number of dead and unkown persons for every year, two and five years, as well as their risk to life. It was verified in the historical change of occurrence number of natural water disasters and number of lost persons that their time sequencies are slightly different, and that they and the risk to life in the disasters have shown remarkablly in some periods showing a periodic occurrence of which the period is nearly 50 to 60 years.By use of the rearranged data of number of lost persons for every five years in the period between 1700 and 1965 AD, it was also shown clearly that the remarkable water disasters take place to concentrate in some periods showing clearly a periodic occurrence of which the period is very close to 55 years being the so-called Yoshimura cycle in the solar activity. Finally, application of the logistic equation to hindcast the total population growth resulted in the fact that three stages exist in the period very clearly, and they correspond to the periodic occurrence of water disasters in the transition period.