Colorado River basin has lost nearly the equivalent of an underground Lake Mead

Tourists look at the Colorado River, which provides water to approximately 40 million people. Photograph: Rebecca Noble/Reuters

The Colorado River basin has lost 27.8m acre-feet of groundwater in the past 20 years, an amount of water nearly equivalent to the full capacity of Lake Mead, the largest reservoir in the United States, a new study has found.

The research findings, based on Nasa satellite imagery from across the south-west, highlight the scale of the ongoing water crisis in the region, as both groundwater and surface water are being severely depleted.