Government’s Latest Damage Forecast for Nankai Trough Mega Quake Shows Quicker Evacuation Is Key To Minimize Casualties

The Yomiuri Shimbun An aerial view of Saijo, Ehime Prefecture, is seen from a Yomiuri Shimbun helicopter on Sunday. The possible areas of flooding in the city increased in the latest damage forecast in the event of a Nankai Trough mega quake. The government’s latest forecast of damage caused by a possible Nankai Trough mega earthquake indicates that quicker evacuations will be the key to minimizing casualties, as the predicted death toll decreased only slightly compared with the figure in the previous forecast made about 10 years ago. Released Monday, the forecast predicts that the death toll will rise in some municipalities because areas with the risk of flooding due to tsunami increased from the previous forecast, even though some progress has been made on implementing prevention measures. With the country’s population increasingly graying, an important task is building systems and fostering awareness among the public to evacuate as quickly as possible in the event of tsunami. Decrease of only 8% At a press conference on Monday, Nobuo Fukuwa, a professor emeritus of Nagoya University who is a member of the group working on the forecast, emphatically said, “Unless damages are reduced, there are concerns about the nation’s future. We want [the government] to take countermeasures more seriously.” The forecast reflected levels of progress in countermeasures for earthquakes and tsunami, data of which was looked at after the previous forecast was compiled for the first time from 2012 to 2013. The latest forecast includes new factors such as the rates of quake-proof capabilities of houses across the nation, the construction of coastal dikes, and buildings and towers to which people evacuate in the event of tsunami. In 2021, there were a total of 12,471 structures to escape from tsunami. The number was not taken into consideration in the previous forecast. Despite the changes for better, the predicted death toll in the latest forecast is up to 298,000, only an 8% decrease from 323,000 in the previous forecast. When looking at the cause of death, the predicted death toll from collapsed buildings decreased 11% to 73,000 and the death toll from tsunami fell 7% to 215,000 in the latest forecast. The decrease in the death toll due to tsunami was small because the total acreage of possible flooded areas, in which water depths will be at least 30 centimeters, expanded about 30% from the previous forecast. “As a result of greater precision of geographical data, places that were newly found to have the risk of being flooded by tsunami increased,” a Cabinet Office official said. The total acreage of possible flooded areas in Ehime Prefecture is predicted to be 8,310 hectares, which expanded 2.3-fold from the previous forecast, and the predicted death toll increased by 12,000 to 24,000. A chief of the Ehime prefectural government’s disaster and crisis management division openly expressed a sense of urgency saying, “In the past 10 years, we have made efforts with concerned municipal governments such as designating buildings that are usable for evacuation, but I’m surprised to learn about the large-scale expansion [of the possible damage areas]. The prefectural government will likely have to review its own prediction.” Fostering awareness The latest forecast indicates death tolls from tsunami in two scenarios with different rates of people who will evacuate immediately. In one, it is assumed that 20% of people will evacuate quickly, and in the other, 70% are assumed to do so. The predictions are based on actual records of the early evacuation rates in tsunami disasters in the past. The predicted death toll becomes the highest if the rate is 20%, halves if the rate is 70% and falls by 70% if the rate is 100%. When the central government compiled a basic disaster prevention promotion plan in 2014 based on the previous forecast, it set a goal to reduce the potential death toll by 80% in the coming 10 years. However, a government official in charge of the issue said, “Raising the percentage of people who will quickly evacuate is essential to achieve the goal.” In fiscal 2023, the Cabinet Office conducted an internet survey on 2,000 people in 139 municipalities in Tokyo and 13 prefectures that are designated as areas needing special attention regarding measures for evacuation in the event of tsunami caused by a Nankai Trough mega earthquake. The result showed only 53% of the respondents replied that they would quickly evacuate. In summer last year, the first-ever information for alerts about a possible mega quake was issued and people’s sense of crisis rose at the time. However, it is still an important task to devise ways to improve and maintain the level of awareness regarding quick evacuation. Takayoshi Iwata, a specially appointed professor at Shizuoka University who is an expert on studies of disaster prevention, said, “While the aging of the population and population decline are progressing, the number of people who have difficulty evacuating quickly and thus are vulnerable to disasters will surely increase. All people in local communities need to be united to consider measures to be taken.” Hard-to-see effects Meanwhile, some officials pointed out that, in the latest forecast, it is difficult to know the effects of countermeasures that have already been taken because predictions were made based on the maximum levels of damage deemed to be scientifically possible to occur. In areas with a risk of being hit by tsunami caused by a Nankai Trough mega quake, coastal dikes along seashores have been built or reinforced based on the lessons learned from the 2011 Great East Japan Earthquake. Predictions in the latest forecast are based on a precondition that the coastal dikes will be destroyed if tsunami pass over them. Such predictions were made because the same phenomenon occurred in the 2011 disaster. In Hamamatsu, which is predicted to be hit by tsunami up to 17 meters high, the municipal government in 2020 built a huge coastal tide wall that is 17.5 kilometers long and 13 to 15 meters high. But the latest forecast predicts that up to 3,560 hectares of the city, mainly in the city center, could be flooded. “The tide wall is designed not to be destroyed even if tsunami waves pass over it. Therefore, it should have the effect of reducing the level of damage,” said a city government official in charge of the issue. “We want to closely watch a damage forecast that the [Shizuoka] prefectural government will assess from now.” Prof. Takeshi Sagiya of Nagoya University, an expert on studies of crustal movements, said, “The assumption of the maximum damages may become a message that local governments’ efforts are useless. The central government should also present improvements in disaster prevention effects of such countermeasures.”