In this study, first, three compact city models with different degrees of compactness for a prefecture in a large metropolitan area of Japan were designed. Based on the urban classifications “population-induced area,” “population-unchanged area,” and “withdrawal area,” we constructed the compact city models. Next, the impact of introducing the designed compact city models on the summer thermal environment in the 2050s was quantitatively assessed by downscaling simulations from a global scale to an urban scale. Moreover, we examined the effect of a land use change in the withdrawal area on the future thermal environment in the urban area (the population-induced and population-unchanged areas). As expected, a temperature increase in the urban area occurred due to urban densification in the compact city models. On the other hand, the temperature decrease in the urban area as a result of changing the land use of the withdrawal area, i.e., by replacing the withdrawal area with grassland, approximately offset the above-mentioned temperature increase. This implies that, in compact city planning, it is necessary to properly plan not only for the concentrated urban area but also for treatment of the withdrawal area from the viewpoint of environmental impact.
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