A Climate Warning from the Cradle of Civilization

“The marshes are drying,” Mohammed Raed, 19, said as he left them behind, walking his family’s emaciated buffalo toward a neighboring province, where there was still the hope of feeding them.

Mr. Sahlani, the science teacher, said people now eyed their upstream neighbors with suspicion, accusing them of taking more water from the irrigation canals than they’re due and then shutting the sluice gates, leaving too little for residents downstream to grow crops.

Without realizing it, he was describing — on a much smaller scale — Iraq’s standoff with Turkey and Iran, which control much of the Euphrates and the Tigris.

“I understand the problem,” said Ghazwan Abdul Amir, the Iraqi water ministry’s director in Naseriyah, adding that the government was hoping to bring more water to residents in the area.

But water is scarce and money is tight, he said: “Maybe next year.”

Fixing Iraq’s outdated farming techniques, which waste as much as 70 percent of the water used for irrigation, according to a study done for Iraq’s water ministry, is paramount. But persuading…