What is a Desert?

I've been writing about deserts for awhile, but it seems that it might be a good idea to define what a desert is. The most basic definition is that a desert is an area that is moisture deficient; more water evaporates than is received. Another definition, more quantitative in nature, says areas that receive no water for at least 12 consecutive months are extremely arid lands, those that receive less than 10 inches (less than 250 mm) a year are arid lands, and those that receive 10-20 inches (250-500 mm) a year are semiarid lands (steppes rather than deserts).

One of the characteristics of deserts is that they have large temperature fluctuations due to the lack of humidity. Daytime and nighttime temperatures may vary by over 50 degrees Fahrenheit (10 deg C). (Keep that in mind if you're packing for a trip to the desert!)

Deserts are not necessarily hot. Antarctica classifies as a desert because of the small amount of precipitation it receives. In fact, over one-third of the land masses on our planet are considered to be deserts. Sand covers only about 20 percent of deserts, with a variety of soils, bare rock, and even ice constituting the other desert bottoms.

The word desert is derived from the Latin desertum, which means "unpopulated place." That was largely true at one time, but due to humans creating diversions and developing the combustible engine that pumps groundwater up to the surface, over 500 million people live in the deserts. Desert cities include Phoenix, Arizona; Riyadh, Saudi Arabia; Greater Los Angeles area, California; Dubai, United Arab Emirates; Juarez, Mexico; and many others.

Although at first it might appear that few plants and animals live in deserts, biodiversity is often high. Animals might not be readily seen because some spend part of their lives in burrows to escape temperatures that are not conducive to their lifestyles, while others are primarily active at night. Some animals (like kangaroo rats) have evolved to be able to live without drinking water by creating water during metabolic processes when they digest food. Plants are often drought- or salt-tolerant to be able to withstand the harsh conditions. Some desert plants have long taproots to be able to reach underground water.

Humans have adapted to survive in the desert by being nomadic to find food and water sources. Traditional desert dwellers include the Bedouin, Tuareg Tribe, and Pueblo people, who live in hot deserts, and the Inuits, who live in a cold desert. Many more people have moved to the desert in the last 75 years due to the invention of air-conditioning and highly engineered water systems.

The Four North American Deserts

In an earlier post, I briefly mentioned the four North American deserts. Now I'll describe them in a bit more detail.

Sagebrush in the Great Basin Desert

Great Basin Desert

The Great Basin Desert is the biggest North American desert, covering most of the state of Nevada and extending into the states of Utah, Idaho, Oregon, and California. It is the only North American desert considered to be a cold desert, which is largely a function of its high elevation, with most basins above 4,000 feet in elevation, and mountaintops over 13,000 feet. Average annual precipitation is 6 to 12 inches. The term Great Basin originates from the fact that the water that falls in the Great Basin does not drain out to the ocean, but stays within the basin. It's really a bunch of basins separated by mountain ranges, but somehow trying to say that succinctly isn't easy.

The primary plant in the Great Basin Desert is sagebrush (Artemisia tridentata), a fragrant green-gray shrub that grows up to several feet high. Several species of sagebrush grow in the desert. Other common plants are winterfat, greasewood, rabbitbrush, and saltbush. Salt Lake City, Utah and Reno, Nevada are in the Great Basin Desert.

Lechuguilla in the Chihuahuan Desert

Chihuahuan Desert

The Chihuahuan Desert is the spiny desert, with lots of sharp plants. It is found primarily in Mexico, but a small portion creeps across the border and into New Mexico and Texas. It's the coolest of the hot deserts, with elevations ranging from 1,200 to 6,000 feet, and it receives up to 10 inches of precipitation annually.

While creosote bush and ocotillo are common, the distinctive plant in this desert is the lechuguilla (Agave lechuguilla). It's a member of the Agave family and has razor sharp spines. Other spiky plants are other agaves, yuccas, sotols, thorny mesquites, and a variety of cacti. El Paso, Texas and Carlsbad and Roswell, New Mexico are within the Chihuahuan Desert.

Saguaro cactus in the Sonoran Desert

Sonoran Desert

The Sonoran Desert is the neat cactus desert, with the characteristic saguaro cactus (Carnegiea gigantea) holding up its arms. In addition to this charismatic character, the Sonoran desert has the greatest species diversity of all North American deserts, despite being the hottest of the four deserts. 

Precipitation ranges from less than 2 inches to more than 12 inches. The desert creeps into southern Arizona and California, but the majority of it is found in Mexico. Phoenix and Tuscon, Arizona are part of the Sonoran Desert.

Joshua tree in the Mojave Desert

Mojave Desert

The Mojave is the smallest of the four North American deserts, but what it lacks in size it makes up in character. This is the desert with the Dr. Seuss-like Joshua trees (Yucca brevifolia).

The Mojave Desert is found between the Sonoran and Great Basin deserts in California, Nevada, Utah, and Arizona. It is a transition area between the two deserts, ranging in elevation from 2,000 to 4,000 feet on average, although it also includes Death Valley which descends below sea level and Mt. Charleston at over 11,000 feet. This is the driest of the four deserts, with 2 to 5 inches of annual precipitation. Las Vegas, Nevada and Palmdale, California, St. George, Utah, and Lake Havasu City, Arizona are in the Mojave Desert.

So in summary:

Largest Desert: Great Basin (or Chihuhuan based on some maps)

Smallest Desert: Mojave

Hottest Desert: Sonoran

Driest Desert: Mojave

Best Desert: You decide

A great resource for learning more about these deserts and the plants that live in them is Ronald J. Taylor's Desert Wildflowers of North America. And now Desert Boy, Henry, and I are going to head outside to go enjoy another desert adventure.