Scientists divide the desert biome into four types: hot and dry, semiarid, coastal and cool. All major deserts of North America are hot and dry: Chihuahuan, Sonoran, Mojave and Great Basin. In these deserts the lack of moisture in the air results in hot days and cold night. Semiarid deserts are quite hot in the summer days but cool in the evenings. Coastal deserts are warm in the summer and cool in the winter, while cool deserts--such as the Antarctic desert--will have snow in the winter and rains in the summer.
It is very rare to find a canopy of vegetation in a desert. The plants that have adapted to the extreme conditions are mostly sparse, low shrubs. Leaves are small and thick, reduced in some plants--such as the cactus--to spines that shade the surface just enough to reduce transpiration. Some plants have silver or shiny leaves in order to reflect more radiant energy. Others open only at night.
Don't look for many large mammals in deserts. Big animals usually cannot store enough water to withstand the desert heat, especially important since a desert does not provide much shade or shelter from the sun. Small mammals do better, but the dominant animals of warm deserts are reptiles. Many desert animals are inactive while it is hot and only come out in the early morning or late evening when the air is cooler.
Although it is lack of water that defines a desert, deserts do get rain. In fact, storms can be violent. Once 44 mm, or 1.7 inches, of rain fell in the Sahara in just three hours. Although that was a record, storms in the Sahara regularly deliver a lot of rain in a very short time. Arroyos--dry stream channels--fill quickly with heavy rainfall and become dangerous. As the U.S. Geological Service warns: "More people drown in deserts than die of thirst."
Hot deserts can get up to 120 degrees F (49 degrees C) although the mean annual temperature ranges from 68 to 77 degrees F (20 to 25 degrees C)--the same as summer averages for semiarid deserts. Coastal deserts are cooler, between 55 to 75 degrees F (13 to 24 degrees C) in the summer, with winter temperatures of 41 degrees F (5 degrees C). Cool deserts can dip to 25 degrees F (-4 degrees C) in the winter.