A harvester rumbles through the fields in the early morning light, mowing down rows of corn and chopping up ears, husks and stalks into mulch for feed at a local dairy.

The cows won’t get their salad next year, at least not from this farm. There won’t be enough water to plant the corn crop.

Climate change, drought and high demand are expected to force the first-ever mandatory cuts to a water supply that 40 million people across the American West depend on — the Colorado River. The U.S. Bureau of Reclamation’s projection next week will spare cities and tribes but hit Arizona farmers hard.