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How can intensive irrigation cause soil salinization in Mesopotamia?

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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.

In the Tigris-Euphrates river system, intensive irrigation causes soil salinization through a combination of water application and inadequate drainage.12

The process occurs as follows:

Mineral Activation: Irrigation water sourced from the rivers naturally contains small amounts of dissolved salts. When this water is applied to fields, it activates mineral residues already present in the soil.1
Evaporation and Accumulation: In the region's hot, arid climate, high rates of evaporation draw soil moisture upward. As the water evaporates from the surface, it leaves behind these dissolved salts and minerals.134
Lack of Drainage: Because of poor drainage systems, the water does not move downward through the soil profile to flush these salts away. Consequently, the salt concentration at the surface increases over time.132

This accumulation of salt is detrimental to agriculture, as it inhibits plant growth by causing dehydration and reducing nutrient uptake. If left unmanaged, this process progressively destroys the soil, eventually forcing farmers to abandon their fields.3412