Colorado River’s below-ground reservoir is shrinking, researchers say

The Colorado River Basin’s hidden, below-ground reservoir — which spans parts of Colorado and six other states — has lost about 13 trillion gallons of water, and it’s shrinking faster than it has in the past, according to researchers at Arizona State University.

Groundwater, stored in the cracks in rock and spaces between soil and sand below our feet, is the oft-overlooked stepchild of the basin, which provides water to 40 million people around the West. Policymakers, water managers and others spend much of their time talking about the basin’s shrinking above-ground supplies — even more so since two reservoirs, Lake Mead and Lake Powell, fell to historic lows around 2022.

Meanwhile underground, more than a Lake Mead-worth of water has disappeared, according to a study published May 27