In ancient times, one technique for farming in desert conditions was runoff farming. In many deserts, the land receives far too little water to support a crop or even to sustain a tree. Usually the rain comes in large quantities when it comes, and there are long periods of time with no rain. If a desert area receives an inch of rain, no plants can be grown. However, if an area adjacent to the field or to a tree is sloped to send any water recieved to a neighboring field or tree, or to a cistern or pond, the water from the infrequent rains can be used to maximum advantage. The collection areas are called catchments, and may be 25 times the size of a neighboring field. A tree can have a fan shaped catchment adjacent to it, with all the water from the catchment running toward the tree, where it may be collected in basins, and basically stored in the soil around the tree. In this way a land that receives an inch of water per year, can be made to grow crops as if it received 25 inches per year.
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