A new study has unveiled a comprehensive breakdown of water usage within the Colorado River Basin. It reveals that alfalfa, primarily utilized as livestock feed, outstrips all urban and industrial water consumption in the region.
The study, published in Communications Earth and Environment in March 2024, details how the Colorado River—used by 40 million people and over 4 million acres of cropland—faces mounting challenges due to decades of persistent water overuse and drought.
Researchers in the study have ties to various universities, including Virginia Tech, Utah State University and University of California, Davis. The lead author, Brian D. Richter, is affiliated with the World Wildlife Fund. Richter designed the study, compiled and analyzed data, wrote the manuscript and supervised co-author contributions.
The researchers used authoritative primary data sources and advanced modeling techniques to construct a comprehensive water budget, focusing on average consumptive water use from 2000 to 2019. Their assessment encompassed direct human activities across municipal, commercial, industrial (MCI) and agricultural sectors and indirect losses due to reservoir evaporation and riparian/wetland evapotranspiration.
“Detailed knowledge of how and where the river’s water is used can aid the design of strategies and plans for bringing water use into balance with available supplies,” the study said.
The Bureau of Reclamation (BOR), responsible for managing the extensive water infrastructure in the Colorado River Basin, has historically been the primary entity accounting for Colorado River water. However, the study reports that the BOR’s accounting, which excluded nearly one-fifth of the river’s water and Gila River contributions, has led to inaccuracies and uncertainties in understanding the river’s water distribution.
“We hope that this new accounting will add clarity and a useful informational foundation to the public dialog and political negotiations over Colorado River Basin water allocations and cutbacks that are presently underway,” the study said. “Because a persistent drought and intensifying aridification in the region has placed both people and river ecosystems in danger of water shortages in recent decades, knowledge of where the water goes will be essential in the design of policies for bringing the basin into a sustainable water supply-demand balance.”
Findings
The findings noted that during the study period of 2000-2019, an estimated 19.3 million acre-feet (an acre-foot is 325,851 gallons) of water was consumed each year before reaching its now-dry delta in Mexico.
The study found that irrigated agriculture accounted for 74% of direct human usage and 52% of overall consumption. Alfalfa and other grass hay constituted 46% of total direct water consumption for agricultural activities and 32% of total water consumed in the basin.
The study also found that a considerable portion of water (19%) sustains the natural environment, primarily through riparian and wetland vegetation evapotranspiration along river corridors. Prior assessments of riparian vegetation consumption had solely focused on the mainstem of the Colorado River below Hoover Dam, omitting vegetation upstream of Hoover Dam and along tributary rivers.
Moreover, 11% of all water consumed within the Colorado River Basin is lost through reservoir evaporation.
In the Upper Basin states of Colorado, New Mexico, Utah and Wyoming, alfalfa and other hay crops account for 90% of irrigated agricultural water use, three times the combined consumption for municipal, commercial and industrial purposes. Overall, agriculture accounted for 48% of water usage from the Colorado River in the Upper Basin. Evapotranspiration was second in usage at 24%.
The researchers noted the decline in water consumption in the Lower Basin between 2000-19, with reductions of 38% in the MCI sector and 15% in the agricultural sector, partly attributed to the policy agreements enforcing water-use reductions.
For the Lower Basin states of Arizona, California and Nevada, agriculture accounted for 54% of water usage, followed by MCI usage at 21%. The Gila River Basin was evenly split between evapotranspiration at 35% and agriculture at 34%.
In Mexico, irrigated crops represent the largest share of water consumption, accounting for 86% of all direct human uses and 80% of total water consumed.
Richter estimated in another study in 2023 that a reduction of 2.4-3.2 million acre-feet per year—equivalent to 22-29% of direct use—will be necessary to stabilize reservoir levels. — Charles Wallace, WLJ contributing editor
