Deserts and tundras

Deserts are part of a wide classification of regions that, on an average annual basis, have a moisture deficit Measurement of rainfall alone cannot provide an accurate definition of what a desert is because being arid also depends on evaporation, which depends in part on temperature. For example, Phoenix, Arizona receives less than 250 millimeters (10 in) of precipitation per year, and is immediately recognized as being located in a desert due to its arid adapted plants. The North Slope of Alaska's Brooks Range also receives less than 250 millimeters (10 in) of precipitation per year and is often classified as a cold desert. Other regions of the world have cold deserts, including areas of the Himalayas and other high altitude areas in other parts of the world.Polar deserts cover much of the ice free areas of the arctic and Antarctic.An alternative definition describes deserts as parts of earth that don't have a sufficient vegetation cover to support human population.