Abstract
Japan faces challenges such as increased underutilized land due to population decline and increased flood risk due to climate change. Green infrastructure initiatives have been promoted in recent years to address these challenges. One of the objectives of green infrastructure is “appropriate management of underutilized land,” but it is still unclear how to promote the introduction of green infrastructure to underutilized land. Therefore, this study quantitatively evaluated the effect of converting future low-underutilized land, especially vacant houses, to green infrastructure, focusing on the amount of stormwater runoff. In the target area, the Jijugawa River watershed in Yokohama, the number of vacant houses in 2040 was projected. It was found that if 75 % of empty houses were converted to green infrastructure, stormwater runoff would be reduced by 6.6 % compared to the 2020 level. The cost-benefit ratio of converting 75 % of vacant houses to GI in 2040 was 18.1 %. In this cost-benefit analysis, only stormwater runoff decrease was considered as a benefit. This result leaves the possibility that the benefits may exceed the costs by accumulating other benefits of the green infrastructure.
