ABSTRACT
In Kansas and other regions of the world, the proportion of water returned to the atmosphere by evaporation may be 90% or more (Rosenberg 1974, p. 160). Many schemes have been proposed to obtain water for these dry regions: arti£cial rainmaking, sea-water distillation, and towing icebergs to regions where the melted water can be used for irrigation. However, manipulations of evapotranspiration (ET) itself may be the best way to conserve water, because so much water is lost by ET. As we shall see in this chapter, one way to conserve water may be to grow plants under elevated levels of CO2. Before we look at the effects of elevated levels of CO2 on water conservation, we £rst de£ne ef£cient water use and look at its historical aspects.
