The architect of the Grand Canyon — the Colorado River — is the lifeblood of the West. The river and its tributaries supply water to more than 40 million people in several major cities, including Las Vegas, Los Angeles, San Diego and Phoenix.

New research has found that more than half of the mighty river’s total annual water flow is being used to irrigate agricultural crops, depleting this essential water source.

“Persistent overuse of water supplies from the Colorado River during recent decades has substantially depleted large storage reservoirs and triggered mandatory cutbacks in water use,” the study said. “Barely a trickle of water is left of the iconic Colorado River of the American Southwest as it approaches its outlet in the Gulf of California in Mexico after watering many cities and farms. Despite the river’s importance to more than 40 million people and more than two million hectares (>5 million acres) of cropland… a full sectoral and crop-specific accounting of where all that water goes en route to its delta has never been attempted, until now.”

The study, “New water accounting reveals why the Colorado River no longer reaches the sea,” was published in the journal Communications Earth & Environment.

The Colorado River’s water levels have been at historic lows because of the ongoing megadrought in the West adding to perpetual overuse. But even though the region is ecologically and economically reliant on the river, a water budget had not been calculated, a press release from Nature Publishing Group said.

The researchers calculated the Colorado River basin’s water budget by looking at the river’s average yearly water use and losses from 2000 to 2019. They took into account all direct human uses — industrial, commercial, domestic and irrigation — as well as indirect losses such as evaporation from wetland vegetation and reservoirs.

“Irrigated agriculture is responsible for 74% of direct human uses and 52% of overall water consumption. Water consumed for agriculture amounts to three times all other direct uses combined,” the study said.

Grass hays like alfalfa grown for cattle feed made up 46 percent of the direct human water consumption from the 1,450-mile river.

The research team found that 32 percent of total water consumption was used to irrigate cattle feed crops.

Water used to irrigate agricultural crops accounted for roughly three times the amount used by cities, reported NPR.

“We consume every single drop,” said Brian Richter, lead author of the study and a World Wildlife Fund senior freshwater fellow, as NPR reported.

In the Upper Basin of the river, irrigation made up almost 90 percent of water usage.

“It is a fact that agriculture uses a lot of water,” said Sharon Megdal, director of University of Arizona’s Water Resources Research Center, as reported by NPR. “I think our ability to adapt is being tested and will continue to be. But I have some confidence that we will be able to.”

The team came up with the first complete Colorado River water budget that included never before reported factors such as Mexico’s overall water consumption — at seven percent — and the total water consumption for the Gila River basin in Arizona, one of the river’s main tributaries, at nine percent, the press release said.

The researchers said a significant reduction in use would need to be made to avoid shortages in the future. More water would also need to remain in the Colorado to support ecosystems along the river’s full length.

“We all need to become far more water literate because there are some hard choices ahead,” said Felicia Marcus, former California State Water Resources Control Board chair and a Stanford University Water in the West Program fellow, as NPR reported.

Negotiations regarding how the increasingly scarce water in the Colorado will be shared by the federal government, Native American Tribes and users in seven states are ongoing. Current guidelines are set to expire in 2026.

“Right now there’s very intense negotiations taking place over how the river’s water will be shared in the future,” said Richter, as reported by NPR. “We wanted those negotiators to have these data in front of them so those debates could be well-informed.”

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