The human imprint on the hydrological cycle is now apparent on a global scale. About 40 percent of the total global runoff (blue water) is now intercepted by large dams and impounded before it flows to the oceans. In many parts of the world, extraction of water from river systems has become so complete that about 25 percent of the worlds rivers run dry before they reach the ocean. In other parts of the world, such as the central United States and the Chad Basin in Nigeria, extraction of groundwater is occurring at rates much higher than recharge flows, leading to the eventual depletion of the resource.
Published in Water Front Magazine No. 3-4 2009.
