Human Vulnerability Index for Evaluating Tsunami Evacuation Capability of Communities

Abstract eng:
Mortality rates caused by tsunamis vary from community to community, depending on geographical and social features peculiar to each. If the relation between mortality rate on the one hand and geographical and social features on the other can be quantitatively formulated, it can be a means to concretely evaluate the community’s vulnerability with regard to evacuation (hereafter, evacuation vulnerability) and to adopt measures that effectively reduce loss of human life. Therefore, the authors proposed to apply an HVI (Human Vulnerability Index), defined as the rate of mortality divided by the rate of incidence of damaged buildings, to evaluate the evacuation vulnerability of a municipality. Factors associated with a tsunami hazard, such as tsunami height, should be omitted from the HVI when evaluating the vulnerability of a community. Therefore, as the most appropriate parameters in the formula, the authors selected the incidence of washed-away buildings as that of damaged buildings. Then, using reliable public databases, the authors evaluated the HVIs of the twenty municipalities that were heavily damaged by the tsunami of the 2011 Great East Japan Earthquake. Through comparison of these twenty HVIs with geographical and social factors of the corresponding municipalities, the following quantitative relation between HVI and specific factors were observed: 1) Tsunami arrival time after earthquake divided by length of evacuation route lowered HVI, which meant the allowance of safe evacuation increased. 2) Rate of car evacuees multiplied by car speed, which meant the capacity of evacuation road, pushed down HVI. 3) People's cognition rate regarding the large tsunami warning issued by JMA soon after the earthquake and the forecast tsunami heights initially broadcast to the municipalities’ areas were sensitive to HVI. HVI of the 3 meter area was higher than that of the 6 meter area. 4) Disaster education such as letting people prepare emergency bags was always effective in lowering HVI A simple regression analysis applied to the above factor-HVI relations did not show enough correlation. However, a multiple-regression analysis using the above four factors as explanatory variables extracted a balanced and reliable formula, which enables us to evaluate the HVI of a municipality before it suffers a large tsunami, although some municipalities may need to improve their databases to express the explanatory variables numerically. HVI and the formula for its prediction provide an effective tool for a municipality to assess its evacuation vulnerability specifically, to set a numerical goal for which its effort and resources should be concentrated and to judge its attainment of vulnerability lowering.

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