The Colorado River running through the Grand Canyon.
Credit: istock

The south-western United States is almost certain to experience a “megadrought” lasting decades if global warming continues unchecked, researchers have warned.

The once-mighty Colorado river, which has regularly failed to reach the ocean since the 1960s, is already in the grip of the worst 15-year drought on record with the flow of water in the 21st century nearly a fifth lower than the 20th-century average, a new study found.

And scientists warned the river could be reduced by anything from 35 to 55 per cent by the end of this century if nothing is done to reduce greenhouse gas emissions.

Rising temperatures cause increased evaporation from the river, but also prompt plants to use more water.

A paper about the study in the journal Water Resources Research said: “With continued anthropogenic [human-caused] warming, the risk of multi-decadal megadrought in the Southwest increases to over 90 per cent over this century if there is no increase in mean precipitation.

“Even if […]