Measuring and Modeling the Sustainability of Global Water Resources

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Shinjiro Kanae Abstract

Conventional water stress assessment is not sufficient for measuring the sustainability of world water resources. Instead, a set of projections performed by an integrated water resources model is necessary. Such a model must represent temporally varying natural and anthropogenic water cycles, along with the representation of the role of "green" water. Measurement of sustainability does not necessarily depend on water stress, i.e., the ratio between water withdrawal and water availability; rather, it should depend on the services and impacts achieved. A prototype of such an integrated water resources model is available, although further development is necessary. For full model operation, data on water availability and withdrawal are indispensable. However, the data, particularly those related to human activities (e.g., water withdrawal, ground water depletion, and infrastructure development) are still sparse and uncertain, in particular for regional assessments. To complicate matters, the networks that observe water availability are shrinking. Therefore, a globally coordinated effort is necessary for data acquisition and management. Finally, even with successful model projection, criteria for evaluating sustainability remain an unsolved issue, partly because we need to consider ethical aspects, such as what constitutes the basic needs of human beings.


Water is a natural resource unlike most others in that it is continuously circulating. Hence, the flow of water, instead of the stock of water, is the primary quantity of importance for assessing availability and sustainability. The total amount of water on Earth changes only on geological timescales or longer. For most other natural resources, such as minerals and fossil energy, stock is the vital parameter, although flow is gradually also becoming important in assessing sustainability in these cases.

Water Scarcity Index

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Water Scarcity Index

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