Two years into California's drought, Donald Galleano's grapevines are scorched shrubs, their charcoal-colored stems and gnarled roots displaying not a lick of life. "I've never seen anything like this," says Galleano, 61, the third-generation owner of a 300-acre vineyard in Mira Loma, California, that bears his name. "It's so dry ... There's been no measurable amount of rain."

California is experiencing its worst drought since record-keeping began in the mid 19th century, and scientists say this may be just the beginning. B. Lynn Ingram, a paleoclimatologist at the University of California at Berkeley, thinks that California needs to brace itself for a megadrought—one that could last for 200 years or more.

As a paleoclimatologist, Ingram takes the long view, examining