Water in the Colorado River Basin, a vital source for over 40 million people, has vanished at an alarming pace over the past 20 years, a new study has found.

The Colorado River Basin spans over 246,000 square miles and supplies water to seven US states, including Colorado, New Mexico, Wyoming, Arizona, Nevada, and California.

Researchers used more than two decades of satellite data to track water loss in the region. 

Between April 2002 and October 2024, the basin lost more than 13 trillion gallons of freshwater that is nearly two-thirds of it from underground reserves.

Since 2003, nearly 28 million acre-feet of groundwater roughly the full capacity of Lake Mead has depleted, driven by unregulated pumping and drought.

They used data from NASA to monitor underground water loss.

It shows that since 2015, the groundwater has been depleting 2.4 times faster than surface water, marking a sharp acceleration in water loss.

The groundwater loss is driven largely by over-pumping in the Lower Colorado River Basin, particularly in Arizona, Nevada, and California where regulation is minimal or nonexistent.

Professor Jay Famiglietti, the study's senior from Arizona State University, said: 'Everyone in the US should be worried about it, because we grow a lot of food in the Colorado River Basin and that's food that's used all over the entire country.' 

The Colorado River and its underground supply support everything from drinking water for cities like Los Angeles and Phoenix to massive agricultural operations growing water-heavy crops like alfalfa, much of which is exported.

'Over-pumping is the main cause of groundwater losses over the past 20 years,' Professor Famiglietti said. 'There's nothing illegal about it, it's just unprotected.'

The Colorado River Basin has long depended on snowmelt from the Rocky Mountains to refill its rivers, reservoirs, and aquifers. 

But rising temperatures and droughts, driven by climate change, are shrinking snowpack and reducing surface water flow.

The decreasing supply of surface water is visually apparent throughout the region. 

Lake Powell and Lake Mead have seen sharply falling levels, and the Colorado River's overall flow has diminished, a trend researchers say will likely continue if warming intensifies.

As surface water becomes less reliable, cities and farms are leaning more heavily on groundwater but that safety net is also collapsing.

'We used to say the Colorado River is the lifeblood of the western US,' Professor Famiglietti told The Guardian. 'Now it's becoming clear that groundwater is the lifeblood and it's vanishing.'

The study highlights that the Lower Basin including Arizona, Nevada, and parts of California has been hit hardest. Groundwater accounts for more than 71 percent of total water loss in that region.

Arizona in particular faces critical risk. Outside of designated management areas, groundwater pumping remains largely unregulated. As a result, wells are drying up, pumping costs are rising, and food security is under growing threat.

As groundwater vanishes, wells run dry, pumping costs rise, and food security is threatened.

About 80 percent of the Colorado River Basin's water goes to agriculture, supporting a $1.4 billion industry in Arizona alone, according to the U.S. Department of Agriculture. 

The new study conducted by Arizona State University offers one of the most detailed looks yet at water loss in the Colorado River Basin.

Since 2015, most of the Colorado River Basin's freshwater loss has been driven by aggressive groundwater pumping in Arizona, where the absence of statewide regulations outside designated Active Management Areas has allowed unchecked extraction for agriculture and growing urban demand.

The research used satellite-based gravity data to measure changes in total water storage including snow, surface water, soil moisture, and groundwater.

The Lower Basin, which includes Arizona, Nevada, and parts of California, was hit hardest, with groundwater making up more than 71 percent of its total water loss.

This isn't the first warning. Previous studies using NASA's data have documented steady groundwater declines in the region between 2003 and 2014. 

But the latest research confirms that the pace of depletion has accelerated, especially since 2015.

The Colorado River's flow has dropped 13 percent below its 20th-century average in recent years, and if current warming trends continue, experts warn it could shrink by as much as 30 percent by mid-century.

States in the region were forced to reach a federal agreement in 2023 to limit water usage and try to protect the river's supply.

The more water that is lost from the river, Professor Famigletti told the Washington Post, 'the more pressure there's going to be on the groundwater' in the basin.

'And then,' he said, 'it becomes a ticking time bomb.'

Meanwhile, demand is only rising, with the region attracting water-intensive industries like data centers and semiconductor factories.