Variations in River Runoff by Continent through most of the 20th Century
River runoff is cyclical in nature, with alternating cycles of wet and dry years. Significant deviations from average values differ in duration and magnitude. For example, 1940-44, 1965-68 and 1977-79 are clearly low periods in terms of total runoff from the world's rivers. During these periods, the runoff was estimated at 1 600-2 900 km3 below the average value. By contrast, 1926-27, 1949-52 and 1973-75 saw much greater levels of river runoff (Shiklomanov, 1999). The last two decades have witnessed increasing runoff in South America and decreasing runoff in Africa.
Year: 2005
From collection: Vital Water Graphics
Cartographer: Philippe Rekacewicz, Delphine Digout, UNEP/GRID-Arendal