If Arizona’s Colorado River water allocation was cut to zero, “we could burn through the available groundwater in 50 years,” Famiglietti said. “We’re talking about decades. That’s scary.

As the Colorado River’s reservoirs have declined, even larger amounts of groundwater have been drained from aquifers. Using satellite data, scientists have estimated the vast water losses.

The Colorado River is running low. The picture looks even worse underground, study says. The Colorado River Basin has lost twice as much groundwater since 2003 as water taken out of its reservoirs ...