More effective use of green water – rainfall stored in soil – could mitigate irrigation demand for some of California’s most important perennial crops. So say US researchers who simulated 13 years’ growth of alfalfa, grapes, almonds, pistachios and walnuts under different irrigation strategies.

Though the Midwest might be America’s breadbasket, in value terms the nation’s agricultural output is dominated by California, which has become a globally significant producer of fruit and nuts.