In satellite images, the farm fields in central Arizona stand out like an emerald green quilt draped across the desert landscape. Seeing it from the ground level, the fields of alfalfa, corn and wheat are interspersed with the furrows of freshly plowed fields. After the cotton harvest, stray fluffy bolls lie scattered on the ground like patches of snow. A large share of the water that flows to these fields comes from the Colorado River, and the supply of water is about to decrease dramatically.