Figure 17.11: The Sahara desert takes up much of northern Africa. The green band below
the sandy Sahara is the Congo. ( 10 )
sun can be merciless and daytime temperatures are extremely hot. Temperatures often
plunge when the Sun goes down and the daily temperature range may be 15° to 25°C (27° to
45°F). Annual rainfall is mostly less than 25 cm (10 inches). The Sonora desert gets much of
its rain in the winter, when storms come in from the Pacific. Summer monsoon rains drop
a great deal of rain in some areas. The existence of two wet seasons a year allows a unique
group of plants and animals to survive in the southwestern deserts.
Vegetation is limited, since water is scarce. Desert plants are adapted to surviving long
periods of drought. Cacti and shrubby plants have wide or deep roots to reach water after
a rain. Many desert plants are able to store water. Some plants lie dormant as seeds, and
bloom after rain falls.
Semi-arid or Steppe (Bs)
Deserts in continental interiors or in rain shadows are found at higher latitudes. Semi-arid
deserts often receive more rain than the arid deserts, between 20 to 40 cm (8 to 16 inches)
annually. Because land areas change temperature easily, these areas have lower annual
average temperatures plus greater annual temperature ranges. In the winter, these climate
zones get very cold under cold high pressure cells. In the summer, they heat up, allowing
air to rise and rain to fall.
In the United States, the Great Plains, portions of the southern California coast and the
Great Basin are semi-arid deserts. The biome is calledsteppe, which has short bunch grass,
and scattered low bushes, or sagebrush (Figure17.13). A steppe has few or no trees because
there is not enough rain for trees to grow.