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Short abstract:

After the 3.11, it was the first time that computer simulation was used to help government officers decide on hazard areas and support their decision on the height of the seawall. However, as discussions progressed, the government abandoned simulation method in order to maintain their early decision

Long abstract:

After the 3.11 disaster, unlike the traditional "reconstruction on high land," Miyagi Prefecture in Japan's Tohoku area implemented reconstruction in the flooded area by defining hazard areas and constructing huge seawall to ensure the city's future safety. This has raised the issue of how to quantify and visualize "future tsunami risk," leading to the creation of new tools and expertise tasked with revealing the possible risk of future tsunamis. Consequently, computer simulation has emerged as an expert scientific tool from the viewpoint of policymakers, with its hazard maps becoming the scientific basis for selecting hazard areas and setting seawall height standards. However, as urban reconstruction and seawall construction progressed, the reliability of computer simulations as scientific evidence was continually questioned until it was declared abandoned in 2020. This article describes how computer simulation built a temporary "navigation platform" within Japan's three-tier government and how this "platform" collapsed by analyzing post-disaster meeting materials from Japan's three-tier government (country, prefecture, city) and interviews with experts from Tohoku University. This study provides insights into the role of expertise in predicting and managing natural risks, revealing the temporality and fragility of this role within Japan's unique political structure.