To explain economic impacts of flood damage due to climate change over time in Japan, this study develops a dynamic spatial computable general equilibrium model, and measures flood damage costs through some numerical experiments. It is inferred that the frequency and the intensity of flood are on the long-term increase. In the category of flood damage in Japan, there are serious flood damages to social capitals. These observations are described in statistical research on flood by Japanese government. In this study, these damages are defined as \u81gthe direct damage\u81h, and are different from decrease in equivalent consumption due to the direct effect. Also, the proportion of the direct damage to decrease in equivalent consumption is defined as \u81gthe dynamic multiplier of damage cost\u81h. This study develops a spatial CGE model based on dynamic structure of the Ramsey model. Our model has 8 regions and 20 production sectors. The flood scenario is described as increase in capital depreciation rate due to flood from 2000 to 2050. In our simulations, 5 flood damage rates are used consisting of damage rates calculating by 4 climate models and uniform damage rate throughout Japan. To consider dynamic spillover effects of flood damage, this study proposes two indices as dynamic damage costs that are comparative static and transition dynamics. The former is the long-term damage caused as the result of shifts from a steady-state equilibrium to another by increasing in the frequency and the intensity of flood due to climate change. On the other hand, the latter is the difference between flood damage costs by a baseline scenario and by a flood scenario, on the transition path to a new steady-state equilibrium. As the transition path can be described, this study shows possible dynamic spillover effects of flood damage over time. The findings in this study are shown below. 1)In 2050, the total amount of flood damage cost is estimated to be from about US$0.4 billion to about US$5.6 billion. 2)The decrease in the rate of investment return by the long-term increase in flood damage causes decrease in savings and consumption, so that the dynamic multiplier of damage cost is estimated to be from 1.2 to 1.7 times
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