## 1 Introduction  
Natural disasters have become more diversified and have increased in both frequency and scale. However, there seems to be an objective limit to what societies can do to prevent them. Unlike social disasters, prevention is essential to avoiding natural disasters and decreasing their consequential damage. As such, both prevention and preparation for natural disasters at the national level emerge as critical issues. Recently, the interest in disaster prevention programs has significantly increased, as has investment in such programs. Since disaster prevention programs should represent a priority, available resources should be utilized to attempt to enhance the efficiency of such programs. Therefore, the evaluation of their economic effects is an essential determinant of investment. However, the evaluation of the benefits and costs of such programs is affected by the general uncertainty in the economic evaluation of public programs, which no theoretical framework has hitherto successfully addressed. However, benefit/cost analyses that calculate the ratio between benefits and costs have been conducted for the evaluation of public policies, such as disaster prevention programs. On the other hand, the efficiency and benefits of preventive disaster management measures in reducing and avoiding disaster impact have been assessed in a limited number of studies. A decision support tool commonly used for estimating the efficiency of such projects is thus the benefit/cost analysis mentioned previously. However, there is a lack of information on the actual costs, benefits, and profitability of natural disaster risk management projects [1]. The benefit/cost analysis model was introduced by [PERSON], et al. [2], who classify the types of disasters in terms of casualties (deaths and injuries), value of the damage to the victims, loss in terms of farm products, and loss in other categories (e.g., building, land, and public facilities). The damage to human lives, severity of the injuries suffered by victims, and other damage categories are assessed through analyzing flooded areas, frequency of floods, and size of damage to agricultural products as a function of flood duration. Table 1 reports the results of case studies in South Korea and other countries, which have analyzed the efficiency of disaster prevention projects using the benefit/cost ratio (B/C). Specifically, Table 1 shows the sources and data assessing potential ex-ante benefits of such projects, as well as those capturing their ex-post benefits. The ex-ante variables include a preliminary feasibility assessment of reclaimed land systems in response to floods by [PERSON] [1; 3], the disaster mitigation project effects of the Federal Emergency Management Agency (FEMA) [4], and the Four Rivers Restoration Project by [PERSON] [5]. The ex-post variables include post-evaluation of flood control in China for the past 40 years by [PERSON] [6]; of a Red Cross mangrove planting project in Vietnam to protect coastal residents from typhoons and storms by the International Federation of the Red Cross (IFRC) [7]; of a disaster prevention and preparedness program by [PERSON] and [PERSON] [8]; and the effects of investment in Korea's disaster prevention by the National Emergency Management Agency (NEMA) [9]. Specifically, [PERSON] and [PERSON] used the internal rate of return (IRR) and net present value (NPV) along with the benefit/cost ratio. In most studies reported in Table 1, direct and indirect economic impacts were considered. The discount rate, for which values ranging between 0% and 20% exist in the literature, is often set to 12% for such projects. In some cases, potential social impacts were also included. In previous studies, it has been shown that the benefit/cost value decreases as the discount rate increase [10]. These studies have conducted a benefit/cost analysis of natural disaster damage; however, their scope was rather limited. In addition, collapse hazard zones have almost never been addressed.