… Pistachios are growing fast in California, where farmers have been devoting more land to a crop seen as hardier and more drought-tolerant in a state prone to dramatic swings in precipitation. The crop generated nearly $3 billion last year in California and in the past decade the United States has surpassed Iran to become the world’s top exporter of the nut. …  Much of the crop is headed to China, where it is a popular treat during Lunar New Year.