Lake Mead’s bathtub ring rises above the surface in February 2018. In the years since, and the weather has continued to be drier and warmer across the Colorado River Basin, which supplies water to 40 million people in the Southwest. (Photo by Luke Runyon/KUNC)
The Colorado River’s two biggest reservoirs are likely to drop to historically low levels later this year, prompting mandatory conservation by some of the river’s heaviest users.
The latest Bureau of Reclamation reservoir projections, which take into account river flows in a given year, show a likelihood that Lake Mead on the Arizona-Nevada line – the nation’s largest reservoir – will dip below the critical threshold of 1,075 feet above sea level in May and remain there for the foreseeable future.
A first-ever official shortage declaration from the Department of the Interior is almost certain later this year. According to the terms of a 2007 agreement among the seven states in the Colorado River Basin, a shortage is declared by the secretary of the interior after consulting with water users in the Lower Basin states of California, Arizona and Nevada. An August report is used to forecast when Lake Mead will be below 1,075 feet at the start of the following calendar year.
Extreme to exceptional drought conditions have blanketed more than 75% of the river’s upper watershed for more than eight months. The majority of the river’s water comes from high mountain snowpack in Colorado and Wyoming. Both states are dealing with drought of varying degrees of severity.
“Current conditions resemble 2002, 2012, 2013 and the beginning of 2018, four out of the five driest years on record,” the Bureau of Reclamation report notes.
Lake Mead and Lake Powell, on the Arizona-Utah line, haven’t recovered from sustained hot and dry conditions for the past 21 years, a trend scientists link to human-induced climate change.
Higher temperatures have increased evaporation from streams and reservoirs, raised demand for water in forests and on crops, and changed precipitation from snow to rain. Snow acts as a large, frozen reservoir that melts slowly over months, while rain is harder to capture and dole out to farmers, cities and other users.
Leading water officials in Arizona and Southern California say they are prepared for the coming cutbacks to their water supplies. If the dry conditions hold, Arizona, Nevada and Mexico could take increasingly steep cuts to what they’re allowed to divert from the river. California also could see its water allocation restricted if the declines continue.
The 246,000-square-mile basin has flirted with a shortage declaration for the past decade but has been aided by short-term boosts in snowpack, coordinated releases of water between Powell and Mead, and voluntary conservation by Lower Basin users. Arizona, Nevada and Mexico have already been curtailed due to restrictions laid out in the 2019 Drought Contingency Plan. A shortage declaration will make those cutbacks even steeper.
In a joint statement, the Central Arizona Project and the Arizona Department of Water Resources assured users that state officials had been anticipating the news.
“The study, while significant, is not a surprise,” the statement reads. “It reflects the impacts of the dry and warm conditions across the Colorado River Basin this year, as well as the effects of a prolonged drought that has impacted the Colorado River water supply.”
Jeff Kightlinger, general manager for the Metropolitan Water District of Southern California, said in a statement the watershed so far has been able to avoid a shortage declaration because of voluntary conservation efforts. But climate change is deepening the Colorado River’s supply and demand imbalance to the point where mandatory cutbacks are coming.
“Unfortunately, it appears that continued hot and dry conditions throughout the basin mean a shortage declaration can no longer be avoided,” he said. “We must continue to work collaboratively as we begin longer-term discussions on how to address the river’s supply imbalance.”
This story is part of ongoing coverage of the Colorado River basin, produced by KUNC in northern Colorado, and supported by the Walton Family Foundation. KUNC is solely responsible for its editorial content.