Where Did All the Water Go? New Study Explores Water Use in the Colorado River Basin.

The remaining 48% is broken down into three categories in the study — about 18% goes to municipal, commercial or industrial uses, while 11% is lost to evaporation in reservoirs.

Evapotranspiration accounts for the last 19%, which Richter essentially defines as water for the river ecosystem, consumed by riparian and wetland vegetation. It’s a novel approach to a study of this nature, Richter said.

“Usually when people do a water budget for a river system, they’re only paying attention to the human uses. We wanted to change that conversation,” he said.

Consider these other key findings from the study:

·  In Mexico, 80% of Colorado River water is used for agriculture, while just 7% is left for the river’s ecosystem and 13% for municipal, industrial or commercial use.

·  The river was overconsumed, meaning more water was taken from the river than was supplied during spring runoff, in 16 of 21 years from 2000 to 2020. Users are overconsuming about 20% of the river’s water, the study found.

·  The lower basin uses more water for agriculture than the upper basin — 54% of Colorado River water in the lower basin (Arizona, Nevada, California and Mexico) is used for crops and livestock, compared with 48% in the upper basin.

·  In the upper basin, 24% of Colorado River water is consumed by the ecosystem compared with 14% in the lower basin.

·  About 15% of the water in the upper basin is lost to evaporation in reservoirs — in the lower basin, that figure is at about 10%.

The study comes as water managers from Colorado River basin states are working on new management plans ahead of 2026, when current guidelines are set to expire. Negotiations are tense, and the states so far have yet to reach an agreement. Meanwhile, scientists estimate flows in the river have decreased by roughly 20% over the last century, with warming temperatures resulting in a 10% decrease in runoff.

Richter said he hopes the study can be of use as negotiations continue.

“We wanted to make sure those negotiators have the most accurate and the most complete estimates of where the water is going as a foundation,” he said.

Kyle Dunphey covers politics, public safety and the environment for Utah News Dispatch. This story first appeared in the Utah News Dispatch. Utah News Dispatch is part of States Newsroom, a national nonprofit news organization.The article was republished in Stateline. Read more Stateline coverage of how communities across the West are grappling with drought that’s worsening because of climate change.