When Gilbert Quintana, a farmer in the Mexicali Valley, learned he would soon lose 15% of his water supply, he did what he's done before in a pinch: buy water from other growers in northern Mexico.

But Quintana worries that such workarounds won't always be possible. The water used to irrigate his 2,000 acres of (800 hectares) of Brussel sprouts, green onions, and lettuce comes from the over-tapped Colorado River, which a megadrought in the American West due in part to climate change is rapidly depleting.