Nearly half of all the world's land drains into the Atlantic Ocean
Follow any raindrop downhill and it ends up somewhere specific. For about 48.7 percent of Earth's land, that somewhere is the Atlantic, fed by rivers from the Great Lakes to the Nile. Another 18 percent never reaches any ocean at all, draining instead into inland seas, salt flats and vanishing lakes.
A drainage basin is the patch of land where all surface water flows to a single outlet, such as a river mouth, lake or sea. Ridges and hills form its rim, the drainage divide. Small basins nest inside larger ones where rivers join. North Americans call the basin a watershed, but elsewhere in the English-speaking world watershed keeps its original meaning, the dividing line itself. Catchment, river basin and impluvium are other names, and mapping boundaries, known as watershed delineation, is routine work in environmental engineering.
The Atlantic's share is huge because it includes two enclosed seas. The Gulf of Mexico and Caribbean collect most of the American interior between the Appalachians and the Rockies, and the Mediterranean, with the Black Sea, gathers much of Europe, Turkey and North Africa, plus east-central Africa by way of the Nile. Nearly all of South America east of the Andes and most of western Europe drain Atlantic-ward too.
The Arctic Ocean takes about 17 percent of the land, including much of Canada and central and northern Russia. The Pacific and the Indian Ocean each receive roughly 13 percent: the Pacific from much of China, Japan, Korea and western North and South America, the Indian Ocean from East Africa, the Indian subcontinent and most of Australia. By area, the Amazon basin is biggest at 7 million square kilometres, ahead of the Congo and the Nile. By volume discharged, the Amazon leads, followed by the Ganges and then the Congo.
Closed, or endorheic, basins send their water inward to a sink: a permanent lake, a dry lake or a spot where it disappears underground. The largest lie in Central Asia around the Caspian and Aral seas. Others include America's Great Basin, which is really a cluster of adjacent closed basins, much of the Sahara, the Okavango in the Kalahari, and inland Australia and Arabia. Where water evaporates at the end, the result may be called a playa, salt flat or alkali sink.
Source: Drainage basin
