On a hot summer day the temperature may fall 30 to 50 F as night approaches, because of the low humidity and lack of cloud cover. Without clouds to hold the heat in, the air rapidly cools. Surface temperatures in direct sunlight are commonly 25 to 50 F warmer than the air temperature six feet above. Temperatures in the shade may be cooler by 20 or more degrees. Winter snow and violent thunderstorms fall on thin, sandy soils that do not retain much moisture.
Plants use a variety of techniques to survive desert extremes.
These annual plants have a short life cycle and include the spring wildflowers that occur in showy abundance early each year. Perennials, plants that live longer than one year, must deal with desert extremes in other ways. Cacti store water within their bodies, blackbrush drop their tiny, leathery leaves in dry weather, and yucca have tap roots up to 30 feet long which are able to reach water deep underground. Many desert plants have lightly colored, highly reflective leaves. Moss, a plant not commonly associated with deserts, thrives because it can survive long periods of drought.