Why is farming in the Gobi Desert mainly limited to river valleys?

Farming in the Gobi Desert is primarily limited to river valleys because the region is an extremely arid environment with very little annual precipitation—often less than 4 inches (100 mm) in many areas.12

The desert's drainage is largely underground, and surface rivers typically have little constant flow, often disappearing into the loose soil or drying up entirely. Because the vast majority of the landscape is a stony, waterless, or salt-affected plain, agriculture is not viable in most areas. River valleys provide the necessary access to water that is otherwise scarce or inaccessible across the broader, parched desert terrain. Consequently, these valleys serve as the only locations where the moisture levels and soil conditions can support agricultural development.324