River runoff represents the accumulated water, from precipitation and meltwater, that feeds into rivers that feeds into seas. The estimated annual figures in this graphic is what volume of water that ends up in the World Ocean. Factors influencing this volume is primarily the area that drains (e.g. area of continent), precipitation and evaporation. Tropical regions typically exhibit greater river runoff volumes. The Amazon carries 15% of all the water returning to the world's oceans, while the Congo-Zaire basin carries 33% of the river flow in Africa. Arid and semi-arid regions, which make up an estimated 40% of the world's land, have only 2% of its runoff (Gleick, 1993).
From collection: Vital Water Graphics
Philippe Rekacewicz, Delphine Digout, UNEP/GRID-Arendal