Desert

Deserts cover about 35 percent of the earth's surface and are mainly located between the latitudes of 5–35 degrees north of the equator. They are regions characterized by high aridity, little vegetation cover and large surfaces of bare soil, and highly adaptable plants and animals that can survive long droughts. According to bioecological definitions, the world's deserts represent all ecoregions of the world that harbor desert vegetation, identified by xerophilous life forms and the general desert-adapted physiognomy of the dominant plants.

Among these, aridity is the most prominent indicator, commonly measured by the Aridity Index, [Page 448]an estimator for the ratio between mean annual precipitation and mean annual potential evapotranspiration, which is less than 1.57 inches (−40 millimeters) for arid deserts and −.79 inches (−20 millimeters) ...