River flow is cyclical in nature, with alternating cycles of wet and dry years. This graphic uses bar graphs to show the average annual volumes of river runoff in cubic kilometres for each continent from 1921 to 1985. Over the time period the discharge there has been no obvious trends, but a certain degree of fluctuation, the level dependent on the area of the basins and the precipitation over the area. The sizes of the bars in this graph reflect the level of precipitation over the respective continents.
From collection: Vital Water Graphics
Philippe Rekacewicz, Delphine Digout, UNEP/GRID-Arendal