endorheic

Endorheic refers to drainage basins and lakes that retain water and have no natural outlet to the oceans. The term comes from Greek endon, meaning inside, and rheic, relating to flow. In an endorheic system, water leaves the basin primarily by evaporation or seepage, causing mineral salts to accumulate and often producing saline or hypersaline lakes and extensive salt flats.

Endorheic basins are common in arid and semi-arid regions where precipitation is low and evaporation is high. The balance between inflow and loss determines lake level and salinity; when inflow is reduced or evaporation increases, lakes shrink and salts concentrate. When inflows rise, water levels can increase, but there is still no outlet to the sea. Groundwater seepage can also act as a loss or, in some cases, a minor outflow path.

Well-known endorheic lakes and basins include the Caspian Sea, the Aral Sea, the Great Salt Lake in Utah, Lake Urmia in Iran, and Lake Tuz in Turkey, as well as salt flats such as Salar de Uyuni in Bolivia. Issyk-Kul in Kyrgyzstan is one of the largest alpine endorheic lakes and is notable for its substantial size despite the absence of an outflow.

Human activities, such as damming rivers and diverting water for irrigation, can disrupt the natural water balance of endorheic basins, contributing to shrinkage of lakes or changes in salinity and ecosystem health. Endorheic systems are a focus of hydrology and climate research, illustrating how closed drainage basins respond to environmental change. See also exorheic, endorheic basin.