THE ROLE OF WATER IN THE LIFE OF ECOSYSTEMS AND OF PEOPLE

The significance of the role of water in the life of planet earth can only be understood fully from analysis of its part in the sustenance of natural environmental systems and in the support of human society. The two aspects are interdependent in the long run, but decisions about one are often made in the short run without regard to effects upon the other, as when a city withdraws stream flow without considering the consequences for fish life, or when wetlands drainage reduces quantity and quality of water for urban use. A persistent challenge is to consider them together. From speculations as to the possible effects of global climate change upon water supply at one extreme of generalization to estimates of the essential daily needs of one isolated family at the other extreme, it is desirable to assess both aspects in relation to each other, as photographs from South and Central Asia in this chapter attest (Figure 1.1).

The problem of viewing the full importance of water on the global scene is introduced by briefly examining the global water budget, how elementary notions of the role of water in global life have evolved, how they at times have been in harmony or in conflict, and how they present themselves in miniature as well as on the world scale.