Estimation of heat, water, and black carbon fluxes during the fire induced by the Hiroshima A-bomb in 1945

The amount of flammable materials in traditional Japanese houses in the Hiroshima region in the 1940s is estimated to calculate heat, water and carbon fluxes during the induced urban fire by the Hiroshima A-bomb in 1945. Traditional houses remaining in the Fukuyama region were examined to estimate the total amount of flammable resources in each house classified into three categories based on number of stories and size of the houses. The density of wood was estimated to be 112 kg m-2 for one-story houses while it was 72 kg m-2 for two-story houses (Okada and Aoyama, 2011). Then, the amount of flammable materials in traditional Japanese houses in each 50-m grid was estimated based on a digital map of the entire city of Hiroshima just before the atomic bombing and a detailed damage distribution map which were both created from the aerial photographs (Koizumi et al., 2011) and . The amount of flammable materials was converted to heat, water, and black carbon fluxes based on the duration of the fire induced by the A-bomb as a function of time and space. The average heat flux in the region was 14.4 kJ s-1 m-2, and it ranged from 0.5 to 96.5 kJ s-1m-2. The average heat flux obtained in this study is about half of a value used in previous study (Yoshikawa, 1999) and is 7 times larger than that in Shouno, 1953. The total heat released during the fire was 7 PJ. In total, 0.22 Tg of water was produced and released during the fire. The total amount of black carbon produced and released during the fire was 0.02 Tg, when we assume that 10% of the fuel was under reducing conditions. To confirm this assumption for under reducting conditions, we prepared dummy black rain sample of which black carbon concentration ranged from 1 % to 70 % and asked witnesses of black rain to choose one of the samples as most similar one with black rain they observed in 1945. 37 replies were obtained and the 34 of 37 replies concentrated with a range from 5 % to 15 %. The time-dependent fluxes of heat, water, and carbon were also calculated.