The Colorado River Basin's groundwater supplies are dwindling, thanks to a combination of both natural events and human pumping activities, a new study has found.

The critical Western system has lost about 42 million acre-feet of water storage since 2003 — with 65 percent of those declines, or 28 million acre-feet, attributable to groundwater depletion, according to the study, published on Tuesday in Geophysical Research Letters.

Over the past century alone, the authors noted, the Colorado River's flow has plunged by about 20 percent, with climate models predicting additional reductions of up to 30 percent by mid-century, due to escalating temperatures and diminishing Rocky Mountain snowpack.

"The decline of the river poses a severe threat to both........

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