Dan Errotabere's family has been farming the dry soils of the western San Joaquin Valley for nearly a century. His grandfather primarily grew wheat and other grains. His father grew vegetables and other annual crops almost exclusively. But in 1999, Errotabere decided to plant his first almond tree. Today, almonds account for more than a quarter of his 3,600-acre farm.

"Out here it's nothing but topsoil," he told me during a tour of his property late last year. He added that his land is especially good for growing nuts.

If there's enough water.

Errotabere's farm resides within the Westlands Water District, a barren landscape southwest of Fresno that gets very little rain — even in non-drought years. The average annual precipitation in the district is just eight inches, and the region suffers from poor drainage, high levels of toxic minerals in the soil, and salt-laden groundwater. "It's really an area that should have never been farmed," said Richard Walker, a retired UC Berkeley geography professor and an expert on agricultural economics.

Yet Westlands is almost all farmland, thanks to water from Northern California and the Sierra Nevada that the federal government pumps out of the Sacramento-San Joaquin River Delta and ships south through a series of canals and aqueducts. Throughout the 20th century, this massive transfer of water turned a large section of California desert into a bountiful — and profitable — farming region.

But ever since freshwater began flowing to the dusty west side of the valley, the landscape has been in constant flux. A decade ago, Westlands' major crop was cotton. But today, almonds are on their way to becoming king. Since 2000, the amount of land dedicated to growing almonds has more than doubled in the district, bringing the total to 75,000 acres. And now about one out of every ten almonds sold in the world comes from Westlands. The only crop more common in the district is tomatoes, which cover 80,000 acres.

Westlands farmers like Errotabere have shifted to growing almonds, and to a lesser extent, pistachios, because of the exploding international demand for them. California produces 80 percent of the almonds sold worldwide, with gross revenues of more than $6.2 billion in 2013 — nearly double what they were in 2009. Last year, almonds were California's most lucrative agricultural export by far. "We have good markets, and we're a global product that's extremely desired," said Richard Waycott, CEO of the California Almond Board.

The global almond boom is being fueled in part by sleek marketing campaigns that have made almonds the nut of choice for consumers. Subway stations in China are blanketed with billboards proclaiming almonds to be a heart-healthy snack that makes people "perpetually feel good" (almond exports to China have more than doubled in the past five years). In Korea, California almonds have been integrated into the storyline of a popular prime-time television show. And in Europe, French and British TV personalities have lauded almonds as a healthy alternative to processed foods.

In the United States, almonds have become a staple for many health-conscious consumers. In its raw form, the "power food" is said to lower cholesterol, spur weight loss, and provide powerful antioxidants such as Vitamin E and manganese. Products like almond butter and almond milk have also become increasingly popular in health food stores.

But growing almonds in an arid climate requires lots of water. In fact, Westlands' almond orchards suck up nearly 100 billion gallons of water a year. Cotton, by contrast, needs 40 percent less water per acre, and tomatoes require about half as much water as almonds.

Also, unlike cotton and tomatoes, almonds are a "permanent" crop, meaning the land they're grown on can't lie fallow when water is scarce. "It means farmers really do need to get a hold of water in dry years in order to keep the trees alive," explained Ellen Hanak, a senior fellow at the Public Policy Institute of California and an expert on water.

Almonds, in short, aren't cut out for droughts. And unless the coming months bring a deluge of rain and snow to California, the almond growers of the western San Joaquin Valley could be in for a catastrophic year. On the last day of January, the state Department of Water Resources said it would cut all water deliveries from California's vast system of reservoirs and aqueducts. The Central Valley Project, which is run by the federal government and provides water to Westlands, may also eliminate water allocations this year. And since tree nuts don't respond well to groundwater in Westlands because of its high salinity levels, the water stoppage could leave the district's almond farmers high and dry. "Every barrier that a grower would never want to experience is being placed before them today," said Gayle Holman, a spokesperson for Westlands.

Errotabere said that, under the best-case scenario, he would have to take 1,000 acres of his tomato and garlic plants out of production to free up water for his 1,000-acre almond grove. Under a worst-case scenario, he may have to uproot parts of his orchard, thereby inflicting a serious financial blow to his farm because it took a lot of time and money to grow his almond trees. "It's starting to get really scary," he said. "I simply don't have the means to farm it all, and when that happens there's lost production, lost labor, lost taxes, lost everything because the ground is doing nothing."