Federal officials say they are ready to have a “candid conversation” about accounting for water lost to evaporation in the Colorado River’s Lower Basin. They are giving states until the end of 2024 to prepare for what would amount to a significant cut in annual water allocations to users in Nevada, California and Arizona.
During a September Colorado River symposium held in Santa Fe, both Interior Department Secretary Deb Haaland and Bureau of Reclamation Commissioner Camille Calimlim Touton told attendees that the issue of evaporation and transit loss in the Lower Colorado River Basin were short-term priorities for their respective agencies.
More than 10% of the river’s water is lost to evaporation from reservoirs, seepage and other losses, according to Haaland’s prepared remarks.
“In these serious times, we need to take the overdue step of assessing how to account for those losses throughout the Basin,” the statement reads. “This is another tough reality that we must work together to address.”
Accounting for evaporation has become a tension point among the river’s users in recent months. States in the river’s Upper Basin -- Colorado, Utah, New Mexico and Wyoming -- are already charged for evaporation from federally-managed reservoirs. An historical quirk left Lower Basin users without that same responsibility. Lower Basin users rely on court decrees that followed the Supreme Court decision in Arizona v. California as some of their governing documents. Those decrees never required accounting of evaporation from Lake Mead, the nation’s largest reservoir.
If federal officials push to change the accounting practices, the result would force a significant amount of water conservation on Lower Colorado River users. Total evaporation and transit losses in the Lower Basin fluctuate annually, but often surpass 1 million acre-feet, roughly equivalent to the amount of water the entire state of Utah uses from the river each year.
Forcing users to account for the losses would tighten current water budgets in states that have come to depend on it, said John Fleck, a University of New Mexico water policy professor.
“It would be a huge change in how water is administered in the lower Colorado River,” Fleck said. “The states, especially California and Arizona, had come to depend on really big allotments that were only possible because we ignored the laws of physics and didn’t account for evaporation and system losses.”
Federal officials in June laid a gauntlet for the river’s municipal and agricultural users. In front of a Senate committee, Touton said the basin required 2 to 4 million acre-feet in conservation in 2023 to stabilize the river’s largest reservoirs.
The federal government was prepared to take action if the users themselves failed to commit to conservation, Touton said. No basin-wide plan to account for that amount of conserved water has coalesced. Following the states’ failure to act, calls for federal intervention have grown louder, Fleck said.
“The underlying problem is that the water users in the Lower Basin have refused to step forward and save themselves by coming up with a plan to reduce their own use,” he said. “So we look for some tool that the federal government could use to force them to save themselves. And accounting for evaporation and system losses has always been hanging out there because it's just nuts that we don't do this.”
Federal officials say they plan to come up with a way to account for that loss by the end of 2024.
This story is part of ongoing coverage of the Colorado River, produced by KUNC and supported by the Walton Family Foundation.
