Deserts are characterized by their rainfall—or rather, their lack of it. Most deserts get less than ten inches of precipitation each year and evaporation usually exceeds rainfall. Deserts – regions where more water evaporates from the ground than is replaced by precipitation – are generally extremely hot, but some, like the Gobi in Asia, experience very cold winters. And deserts that are hot during the day may become cold at night because they lack the insulation provided by clouds and humidity.