How to lose a sea

Start with geography

A sea with no way out

The Aral Sea sits in a closed basin: two rivers flow in and nothing flows out. The Amu Darya arrives from the south-east, the Syr Darya from the east, and the only way water leaves is by evaporating. A lake like that is a balance — inflow against evaporation — and its shoreline sits wherever those two happen to meet.

That makes it unusually sensitive. A lake with an outlet responds to less inflow by discharging less. A closed lake has no such release: reduce the inflow and the surface simply falls until evaporation drops to match. The Aral was the fourth-largest lake on Earth by area, and it was resting on that balance the whole time.

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