Study on the Influence of Future Climate Change on Water Cycle in Urbanized Area of Northern Japan in a Cold, Snowy Region

This study aims to assess the impact of climate change on the water resources of Sapporo, the largest city in Hokkaido. Artificial water cycle systems, which involve dam operation and water intake on the Toyohira River, a water resource of Sapporo, were considered in this study. The water resources of the Toyohira River Basin are heavily dependent on snow cover. The amount of water available for intake is secured by controlling the dams at the upper reaches. It is predicted that, under the future climate in which precipitation in late winter will no longer fall as snow but will instead fall as rain, water use at the lower reaches will be greatly affected by a shift in peak discharge to a period earlier than that of the present. In this study, the changes in the artificial water cycle system of the Toyohira River Basin under the present climate to those under the future climate were estimated by using a snow depth distribution-based runoff model, and an assessment was done to clarify whether the present level of water use with the present level of water intake conditions would be possible under the future climate. This assessment revealed that the change from snow to rain in the future climate will have a considerable impact on future water resources. The flow rate in the future climate will peak one month earlier than in the present climate and the future-climate peak flow rate will decrease by about 40 to 50%. The decrease in flow rate is predicted to occur throughout the year; therefore, there seems to be a possibility that securing the minimum water necessary for citizens' lives will become difficult. The assessment of water resources under future climate change is closely related to residents' lives; therefore, this study is indispensable for the social implementation of measures for adaptation to the future.