The volume of urban water used in Japan has been gradually declining in recent years because of the increase in water saving appliances and water saving behaviours. Changes in household water consumption characteristics affect the extent of the adverse effects caused when water supply restrictions are imposed. These changes must be reflected in reservoir operation plans in times of drought and when developing long-term water resource management plans or water conservation policies. The objective of this study is to quantify the adverse effects of drought associated with changes in consumption characteristics and utilize this in water resource management plans. We use a water consumption model that accounts for changes in household water consumption characteristics, and we apply this model to several droughts in different periods and cities in Japan. Results indicate that reductions in water consumption because of water supply restrictions tend to decrease over time. We concluded that imposing water supply restrictions during droughts has become less effective for maintaining reservoir storage. In designing water resource management plans, it is important to simultaneously evaluate changes in probability of supply-shortage events and the impact of water supply restrictions.

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