What is the maximum amount of rainfall per year for a place to be classified as a desert?

To classify a location as a desert, the defining characteristic is the amount of annual precipitation it receives. Generally, a desert is classified as an area that receives less than 250 millimeters (10 inches) of rainfall per year. This low level of precipitation creates extremely arid conditions, significantly limiting vegetation and wildlife.

Deserts can be hot, like the Sahara, or cold, like the Gobi, but they all share the common trait of having very low annual rainfall. Thus, the threshold of less than 250 mm effectively delineates true deserts from semi-arid regions, which may receive slightly more precipitation yet still experience dry conditions. The classification is based on these precise definitions in climatology, emphasizing the stark difference in moisture availability compared to more fertile or humid regions.

Other thresholds, such as 350 mm or 450 mm, would include areas that may not typically exhibit the arid characteristics we associate with deserts, allowing for additional vegetation and wildlife that wouldn't thrive in a true desert environment. Therefore, less than 250 mm is the most accurate cutoff for identifying a desert.