Largest Drainage Basins in the World

The Atlantic Ocean is the world's largest drainage basin and second largest ocean.
The Atlantic Ocean is the world's largest drainage basin and second largest ocean.

A drainage basin is a place where water collects and then flows into a conventional outlet like a bay or a river. The drainage basin encompasses the surface water and the groundwater. Numerous river branches collect water from different sources and then flows into the mainstream which drains into a more significant drainage basin like an ocean.

Largest Drainage Basins in the World

1) Atlantic Ocean

The Atlantic Ocean is the second largest ocean in the world which occupies a total area of about 41.1 million square miles. The Atlantic Ocean covers 29% of the global water surface and 20% of the world’s surface. It occupies an elongated S-shaped basin which extends longitudinally between Africa and Eurasia to the eastern side and American continents to the west. The Atlantic separates the new water from the old water, and the equatorial counter-current divides it into the south and north Atlantic oceans. The Indian Ocean surrounds the Atlantic to the southeastern side, Pacific to the southwestern side, the Arctic on the north and the southern sea on the south. The Atlantic has a basin area of approximately 26.9 million square miles.

2) Arctic Ocean

The Arctic Ocean is the shallowest and smallest oceanic water body in the world by size; in fact, many oceanographers refer to it as the Arctic sea or the Arctic Mediterranean sea. Situated in the Arctic north polar area, this ocean is surrounded by North America and Eurasia. In winter the sea is usually covered by ice. Due to the massive inflow of fresh water from lakes and rivers and low evaporation, this water body has the lowest salinity level. With a basin area of about 8.9 million square miles, the Arctic Ocean has limited outflow and connection to the surrounding water with high salinity.

3) Pacific Ocean

The Pacific Ocean is the most in-depth ocean on earth and also the largest occupying approximately 63.8 million square miles. Americas surround the Pacific on the eastern side, Australia to the western side and the Arctic Ocean on the northern part. Although it is the most significant ocean on earth, it has the 3rd largest drainage basin which is approximately 7.8 million square miles in area. In fact, both the centres of the western and water hemispheres are in this ocean. The Pacific helps separate the Americas, Australia and Asia.

4) Indian Ocean

Although the Indian Ocean is the third largest oceanic division on earth, it has the fourth largest drainage basin. It is surrounded on the north by Asia and Antarctica on the south and Australia on the east. It occupies about 27.24 million square miles including the Red Sea while excluding the southern ocean. It also has 7.5 million square miles of a drainage basin.

5) Southern Ocean

Also referred to as the Austral or Antarctic Ocean, the Southern Ocean is made up of the south-most waters of the global sea. The Southern Ocean is the fourth largest oceanic division on earth with the fifth biggest drainage basin which approximately 5.4 million square miles. The southern sea is located where the cold water from the Antarctic meets the warm sub-antarctic water.

Importance of Drainage Basins

These basins are essential when it comes to determining the territorial boundaries especially in areas where trading via water plays a crucial role in their economy. They are also the primary source of sediments and water which is collected from the river systems. These basins collect pollutants, sediments, nutrients accumulated as the river flows from the mainland; therefore it plays a vital role in the marine ecology.

Largest Drainage Basins in the World

RankBasinArea (Kilometres Squared)
1Atlantic Ocean69,800,000
2Arctic Ocean23,100,000
3Pacific Ocean20,300,000
4Indian Ocean19,400,000
5Southern Ocean14,000,000
6Mediterranean Sea8,500,000
7Gulf of Mexico/Caribbean Sea6,200,000
8Amazon River6,145,186
9Hudson Bay3,861,400
10Congo River3,730,881
11Caspian Sea3,626,000
12Nile River3,254,853
13Mississippi-Missouri River3,202,185
14Rio de la Plata3,170,000
15Ob River2,972,493

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