Weekly Seminar 14: Challenges of Hydrological Modeling for the Assessment of Sustainability of Water Resources

Speaker:
Dr. Shinjiro Kanae
Department of Mechanical and Environmental Informatics - Tokyo Institute of Technology (TIT)

Summary:
Water is a natural resource unlike most others in that it is continuously circulating. In addition, water as a resource must be inexpensive. High-priced water, such as commercial bottled mineral water, is only useful for very limited purposes. Water is a resource if it is available at a place where it is required, at a time when it is required, with a quality better than required, in sufficient (usually vast) amounts, and at a low enough cost. Water is not a resource as substance for consumption or the source of material, but a resource as medium.
A lot of water crises have been reported throughout the world. However, human beings only use less than 10% of the maximum available renewable freshwater resources. One may therefore wonder why so many water crises emerge around the world. Simply speaking, the reason is the geographical and temporal variability of terrestrial water. Huge amounts of water are available in humid regions, whereas relatively little water is available in regions such as Central Asia, the Middle East, North Africa, the southwestern U.S.A., and much of Australia.
The sufficiency of water resources has been assessed by calculating the ratio between water withdrawal and water availability. The calculated ratio is usually called as “water stress.” However, such conventional water stress assessment is not sufficient for measuring the sustainability of water resources. Measurement of sustainability does not necessarily depend on water stress; rather, it should depend on the services and impacts achieved. For carrying out such a water resources assessment for sustainability, a numerical model that represents temporally varying natural and anthropogenic water cycles along with the representation of the role of “green” water and “virtual” water is useful. A prototype of such a model and preliminary results of the calculation of the model will be introduced in the presentation. In addition to the model, data on water availability and withdrawal are indispensable. Data on the availability of water stocks and the withdrawal from water stocks are also indispensable for sustainability analysis. However, these data such as ground water depletion are still sparse and uncertain. Finally, the linkages of water with other resources and energy will be introduced in the above context; for example, biofuel crop estimation was successfully carried out by this modeling system.

References:
Kanae, S., 2009. Measuring and modeling the sustainability of global water resources, In Graedel T. and E. van der Voet, eds. Linkages of Sustainability. MIT Press.
Oki, T., and S. Kanae. 2006. Global hydrological cycles and world water resources. Science 313:1068–1072.