Humans and the Global Water Cycle
Recent studies, including those by Water Systems Analysis Group researchers, have indicated that direct human manipulation of rivers, groundwaters, upland and coastal river basins may now have detectable signatures at the global scale.
For example, work by Vörösmarty et al. on large river impoundment has documented for the first time a 700% increase in the standing stock of river water and a probable 30% interception of global sediment flux. Using tools already developed to foster regional to global-scale synthesis studies, we are establishing a global geography of emerging water problems and their social implications.
The figure on the right is from Vörösmarty et al (Ambio 2005) and represents the density of human population living above (red) or below (blue) the relative water use threshold of 40% presumed to indicate severe stress. Three examples of the sensitivity in regions located in hydrologically complex transitional zones between arid/semiarid and humid climates are shown.