WHAT IS AN EXORHEIC AND ENDORHEIC BASIN? - GEOGRAPHY - 2025

In hydrology, the exorheic and endorheic basins are the names of the most important systems of irrigation, runoff, drainage and circulation of the bodies of water of the planet earth on the land surfaces.

The basins are the terrestrial areas through which the water of the precipitations and the thaw flows and its final drainage in the different river systems of the territory. From surface irrigation to underground and from small rivers to larger rivers.

The direction and direction of the runoff and drainage of the water will depend on the formations of the different geographical features of the bodies of land, both continental and insular.

This is the main characteristic that defines and differentiates the exorheic basins from the endorheic ones.

What is an exorheic basin?

They are the open systems of water circulation through land surfaces whose main collection and drainage rivers end up flowing into the sea, that is, outside the territory.

These basins present many complex elements and characteristics throughout the water cycle of their entire system.

Open systems contain a wide range of water inlets, stores, flows, transfers, and outlets.

The inputs to an exorheic system are precipitation, both in the form of rain and in solid form of snow or hail, and melting, especially that of the glaciers of the great mountains and ranges.

Storage in the system occurs in large rivers, lakes, swamps, glaciers, portions of land that keep the water absorbed for a long time, wells and underground rivers, and the water stored in the vegetation after the rains. The latter is called “interception”.

The processes of flow and transfer of water in a basin system are filtration into the earth, filtration through permeable rocks, surface runoff, flow through plant stems, and transit through all types of streams., stream or small river.

The elements or processes of water outflow in the system are evaporation, both from bodies of water in open areas exposed to the sun and from the humidity of the plants or the mouth of rivers in the sea.

The exorheic basins of planet earth

Approximately 81% of all areas of the mainland are part of some exorheic basin.

There are 7 exorheic basins on the entire planet that correspond to the 7 great oceanic water bodies and the 2 largest seas.

1- Atlantic Basin

In its northern slope it involves North America, Europe and Africa. It includes the coastal and river territories of eastern North America, from Quebec and Newfoundland in Canada to the Florida peninsula.

In Europe, to the north, it comprises the southern half of the Scandinavian peninsula, all the territories with rivers that flow into the Baltic Sea and North Sea together with Great Britain and France, and finally Portugal and almost all of Spain.

In Africa it involves the western face of Morocco and the Western Sahara. The Seine, Tambre, Minho, Thames, Torne, Draa, San Lorenzo and Hudson rivers flow into the North Atlantic.

On its southern slope it involves Africa and South America. It comprises the territories from the eastern side of the Andes from Venezuela to Argentina, and from Mauritania to South Africa. The Niger, Congo, Orange, Orinoco, Amazon and La Plata rivers are part of this basin.

One particularity of this aspect is that it involves countries that do not have a natural outlet to the sea, such as Bolivia, Paraguay, Niger, Burkina Faso and central Africa.

2- Pacific Basin

It covers the entire western face of the American continent from Alaska to Chile, and East Asia and Oceania from Siberia to New Zealand.

Includes territories with rivers that flow into the China Sea, the East Sea or Japan Sea and the Australasian Seas.

Some rivers that flow into the Pacific are the Sanda, Paz, Tijuana, Suchiate, Alaska, Alsek, Yangtze and Brisbane.

3- Indian Basin

It includes territories on the east side of Africa from South Africa to Somalia, the Middle East and South Asia from the Arabian Peninsula to Indonesia and almost all of Australia.

It includes territories with rivers that flow into the Persian Gulf and the Red Sea such as Iraq, the United Arab Emirates, Sudan, Israel, Saudi Arabia and Egypt, but without the Nile basin.

The Tigris, Euphrates, Great Ruaha, Ganale Dorya, Juba, Ganges and Murray-Darling rivers flow into the Indian Ocean.

4- Mediterranean Basin

It includes the entire southern face of Europe and western Asia from Spain to Israel, and the north face of Africa from Morocco to Egypt. It includes territories with rivers that flow into the Black Sea and the Aegean Sea.

Some rivers belonging to this basin are the Tiber, Muluya, Seyhan, Júcar and the Nile.

5- Caribbean Basin

It includes all the rivers that flow into the Gulf of Mexico from Florida to Yucatán and Cuba, the north face of Central America, north of Colombia, Venezuela and the islands of the Caribbean. The Mississippi, Bravo, Magdalena and Chama rivers flow into the Caribbean.

6- Arctic Basin

It is made up of all the territories on the planet that closely surround the North Pole, Russia, Greenland, Iceland, Norway, a part of Sweden and Finland, almost all of Canada and a portion of Alaska have rivers that flow into the Arctic Ocean.

7- Antarctic Basin

Also called the southern ocean slope, it includes all the rivers of the continent of Antarctica that flow into the sea. It does not involve other territories.

It is a closed system of circulation and drainage of water whose rivers flow into internal bodies of water in the land masses, without any outlet to the sea. Final storage can be in swamps, ponds, or large lakes.

They can occur in all climates and territories, but mainly in three types: lakes trapped within large mountain ranges, in dry areas such as deserts or tundras, and in areas far from the coast in landmasses.

Evaporation plays a crucial role in these systems as they help to maintain the balance of water volumes throughout the seasons.

In some cases, depending on rainfall, endorheic lakes can rise dramatically in level in a short time.

On the other hand, without having another process out of the system, nutrients, contamination and mineral salts are continuously and cumulatively concentrating in the water.

Some endorheic basins of the world

An example of an endorheic lake is the Dead Sea, which has a saline concentration that makes life impossible. Israel, Jordan and Palestine have rivers that are part of this basin like the Jordan.

The Caspian Sea basin is most famous for having the largest internal lake in the world. The territories involved in this basin are Russia, Iran, Kazakhstan, Turkmenistan and Azerbaijan. The Volga and Ural rivers flow into this great salt lake.

In North America there is the Great Salt Lake basin, better known as "Great Salt Lake" in Utah; the Devil's Lake Basin in North Dakota; and the Great Basin which features a lake trapped between the Sierra Nevada and Rocky Mountains ranges.

In Australia there is the Lake Eyre basin in the central desert. This lake has the peculiarity of going empty for several seasons, but when the rivers manage to transport the water without drying up on the way, the lake becomes the largest in the country.

Lake Eyre in Australia

Between Kenya and Ethiopia there is the Lake Turkana basin, which is the world's largest permanent lake in a desert area. In the Sahara desert and the Kalahari there are many endorheic basins that at the end of the system form the famous oases.

In South America there are the basins of the Lake of Valencia in Venezuela, the Mar de la Chiquita in Argentina and many basins with lakes trapped in the Andean highlands such as Lake Titicaca between Peru and Bolivia; which is the largest lake in South America.

References

1. Margaret Cunningham. Drainage Basins: Definition & Characteristics. Study.com.
2. United Nations Environment Program. The Watershed: Water from the Mountains into the Sea - Lakes and Reservoirs vol. 2. Newsletter and Technical Publications. UNEP - Division of Technology, Industry and Economics.
3. Adam Lindquist (2011). Ten Largest Endorheic (Salty) Lakes of the World. Water Connects Us All. Recovered from alldownstream.wordpress.com.
4. The Editors of Encyclopædia Britannica. Drainage basin. Encyclopædia Britannica. Encyclopædia Britannica, inc. Recovered from britannica.com
5. Benjamin Elisha Sawe (2017). Fluvial Landforms: What Is An Endorheic Basin? Worldatlas.
6. Endorheic basin. Recovered from derevolvy.com.
7. A Level Geography. The Drainage Basin Hydrological Cycle.