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Is water a local or a global issue? On one hand it seems very much like a local issue – If a river or aquifer is contaminated by municipal or industrial sewage, the contamination can usually be cleaned up by local wastewater control. And if the local water supply from a river is too unreli- able during particularly dry months, then a reservoir can be built upstream to regulate the supply. On the other hand in our interconnected world, water users in one river basin are strongly linked to users around the world. A good example is the world food market which affects the amount and type of crops grown on irrigated fields around the world. Hence, the use of water for irriga- tion within a watershed will be shaped by a market that extends far beyond its borders. The point is that not only local, but also regional and global forces have an important influence on the use of water and level of water scarcity within a river basin. For that reason a global perspective is needed when assessing the world water situation. This perspective has been taken by the World Commission on Water for the 21st Century1 (referred to afterwards as “the Commission”).

Since 1998 the Commission has been preparing recommendations for the development of world water resources. These recommendations are aimed at governments, institutions, and citizen groups, and will be presented in March, 2000 at the Second World Water Forum in the Hague. The recommendations will be partly in the form of global scenarios which are being prepared by the Scenario Panel of the Commission. These scenarios consist of “storylines” or narratives that describe conceivable future developments of the world water situation. This paper presents the quantification of global water scenarios prepared as part of the work of the Commission. In this paper we take the quantitative and qualitative information in these storylines and convert them into inputs to a global water model, and compute the resulting level of stress on water resources from water use.

The global model we use for the scenario analysis is called the “WaterGAP” model, and it is the first global model that computes both water use and availability on a river basin level. In this pa- per we first describe the WaterGAP model, then report on results of a “Business-as-usual” sce- nario, and a set of alternative scenarios.