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How do dams and reservoirs increase evaporation from the Euphrates River?

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Map showing the Tigris and Euphrates river basin and its drainage network across Turkey, Syria, and Iraq, with color shading for elevation, major dams, canals, lakes, and boundaries with neighboring countries. The green areas indicate lower elevations along the river valleys, while higher elevations are shaded in brown and orange. A small locator map in the corner shows the basin's position within the Middle East. — Tigris-Euphrates river system The Tigris and Euphrates river basin and its drainage network.

Dams and reservoirs increase evaporation from the Euphrates River primarily by creating large, open-water surfaces that are exposed to the atmosphere.12

When the river's flow is impounded behind dams, the water velocity decreases, forming expansive reservoirs such as Lake Al-Asad. These large surface areas significantly increase the total volume of water lost to evaporation, particularly in the arid climate of the region where high temperatures and low rainfall exacerbate these losses. In the case of the Euphrates, the creation of these large reservoirs and their associated irrigation networks has caused the rate of evaporation to increase to as much as 50 percent.312

Beyond direct surface evaporation, these water-control projects facilitate extensive irrigation, which further contributes to water loss through absorption and evaporation across agricultural lands. This process not only reduces downstream water availability but also leads to environmental challenges, such as soil salinization, as mineral residues are left behind when water evaporates from the soil surface.42