Arid Climates

An arid climate is one that receives less than 10 inches (25.4 centimeters) of rainfall in an entire year. Deserts are areas that are arid. Although the most familiar image of a desert involves hot sand, the Arctic North and Antarctica are also deserts, as they also receive little moisture, usually in the form of snow. In contrast, the island of Fiji receives drenching rains for several months of the year, and is located in a tropical area of the world. Fiji receives an astounding 120 inches of rain each year, more than ten times the rainfall that falls in arid areas.

The rain that falls in an arid climate is sporadic and when it does fall, it is usually in the form of a thunderstorm. Flash floods are frequently a danger in arid climates after thunderstorms as the dry, compact soil cannot absorb water quickly enough to capture the rain. Streams swell with water for a few hours and then dry up again until the next cloudburst.

Plants surviving in an arid climate

Plants that survive in an arid climate have adapted to cope with the rare rainfall. Some plants can remain dormant (inactive) most of the time, only growing and reproducing when water is available. This cycle of activity and inactivity that is geared to the availability of water (and sometimes to other factors such as temperature) allows these hardy plants to survive for years.

Other desert plants that grow, bloom, and die each year (annual plants) will quickly go through the life cycle from a seed to a seed-producing plant, and then having their seeds distributed in the few wet days following a heavy rain. These plants will then die and the seeds will lie in wait for the next big rainfall. Surveys of the Sonoran Desert in the southwestern United States have found 10,000 or more seeds in a square yard of soil. For plants like the Desert Sand Verbena and the Desert Paintbrush, this life cycle can be hours or days in length. The brief blooms of these plants turns the desert many beautiful colors.

Plants such as cacti have few or no leaves. This reduces the loss of moisture from the leaves into the air (transpiration) that occurs with plants such as maple trees. To avoid water loss the holes in the leaves of some plants that let moisture out (stromata) can close during the heat of the day and open at night.

Some cacti and other desert plants have long roots that reach far down into the ground to where it is saturated with water (the water table). For example, the roots of the mesquite tree can be up to 80 feet (24 meters) long, the height of an 8 story building.

Animals surviving in an arid climate

Animals and humans also face the challenge of finding water in an arid climate. Even though a streambed (the channel through which a stream runs) may appear dry, flash floods that

Las Vegas Water Use

The city of Las Vegas is located in the desert in Nevada. While Las Vegas was founded in 1855, until the 1940s the area was not heavily populated. Then Las Vegas became known as a resort for gambling and entertainment. Hotels were built and the population began to grow. The population of Las Vegas has grown from approximately 65,000 in 1960 to over 1 million today. The city's population is estimated to double by 2015. Additionally, millions of tourists flock to the area each year.

This population growth, vacation popularity, and increased demands for electricity have put a burden on the water supply of Las Vegas. As groundwater (freshwater in layers beneath earth's surface) has been pumped out to supply the city with drinking water and water for golf course management and other needs, the land in some areas of the city has settled lower by more than 5 feet (1.5 meters). If the amount of groundwater that is being withdrawn continues to be more than the amount of water that flows back into the ground (withdrawal currently exceeds the replenishment by 2 to 3 times), then the situation could become dangerous for the stability of some buildings.

Lower water levels in Storrie Lake, a lake that Las Vegas uses as a water source, has also meant that water rationing is periodically necessary. Water levels in Storrie Lake have dropped by more than 45 feet (14 meters) from levels several decades ago. The rationing of water is necessary to protect the lake from going dry.

fill the bed to the brim with water may leave some water below the surface of the ground. If a hole looks damp when it is dug, then some water is present. Camels conserve water in their fatty tissues for use when sources of water are scarce in the desert, and can drink over 25 gallons (95 liters) of water at one time when a source of water is found. Humans, unable to adapt without water for more than a few days, dig wells and build reservoirs in arid climates to ensure a consistent water supply. As thirsty as a desert traveler might be, the water should not be drunk before it has been treated to kill harmful microorganisms that might be present. Even in an arid climate (microorganisms ordinarily thrive in moist environments) troublesome microorganisms such as Giardia can sometimes be found in natural sources of water. If water contaminated with Giardia is drunk, the microorganisms can cause an intestinal upset.

Dew is another source of water in arid climates. Water that is present in the air as water vapor can change to liquid water on the surface of leaves. Many animals in arid climates, such as lizards, make use of the water provided by dew.

The scarcity of water in an arid climate makes managing the available water resources especially important for those living in this environment. The naturally available water is not enough to supply the needs of all the people in cities in many arid climates. Water is then brought from other regions into these locations adding an expense to the water. Transporting water is typically accomplished by constructing pipelines that funnel water from often far away locations to the arid community.

Brian Hoyle, Ph.D.

For More Information

Books

Abbey, Edward. Desert Solitaire. New York: Ballantine Books, 1990.

Alloway, David. Desert Survival Skills. Austin: University of Texas Press, 2000.

Cromwell, Cathy, and Carole Palmer. Desert Landscaping for Beginners: Tips and Techniques for Success in an Arid Climate. Phoenix: Arizona Master Gardener Press, 2001.

Websites

"How Plants Cope with the Desert Climate." Arizona-Sonora Desert Museum.http://www.desertmuseum.org/programs/succulents_adaptation.html (accessed on August 27, 2004).