On Jan. 17, scientists downloaded fresh data from a pair of NASA satellites and distributed the findings among the small group of researchers who track the world's water reserves. At the University of California, Irvine, hydrologist James Famiglietti looked over the data from the gravity-sensing Grace satellites with a rising sense of dread.

The data, released last week, showed California on the verge of an epic drought, with its backup systems of groundwater reserves so run down that the losses could be picked up by satellites orbiting 400 km above the Earth's surface.

"It was definitely an 'oh my gosh moment,' " Famiglietti said. "The groundwater is our strategic reserve. It's our backup, and so where do you go when the backup is gone?"