The word “desert” comes from a Latin word meaning “abandoned.” How appropriate, because when people think about deserts, they mostly conjure up images of endless sand dunes and desolate stretches of barren land. These images are accurate in some places in the world, but there are different types of deserts. Principally, what makes a desert is an inherent lack of regular rainfall, but scientists use a variety of additional factors to classify deserts into categories (hot and dry, semiarid, coastal, and cold). These factors include temperature, humidity, geology, soil and mineral composition, and the flora and fauna that inhabit the region.
Types of Deserts
Hot and Dry
Hot and dry deserts are classified as being hot throughout the year and very hot in the summer. They receive minimal amounts of rainfall in the winter. Soils tend to be shallow and rocky with good drainage. Plant life includes shrubs, small trees, and cactuses.
Seasons in semi-arid deserts are more defined than in hot and dry deserts. Summers are reasonably hot and dry, and rainfall in winter is minimal. Semi-arid deserts support an assortment of shrubby and grassy plant life.
These deserts are found in areas that are moderately warm to cool. Winters typically are cool and brief, and summers are long and warm. Coastal deserts support a wider variety of plant life than hot and dry or semi-arid deserts.
In cold deserts the main source of precipitation is not rain as in the other types of deserts. Here, moisture comes in the form of snow, ice, or fog. Many of these deserts are found at high elevations and support little life, if any.
Why are Deserts so Hot?
In most places around the world, moisture in the air prevents the sun’s rays from completely penetrating the atmosphere, allowing a ‘moisture blanket’ to protect the Earth from the sun’s intense heat. But in deserts, humidity is low, and the moisture content in the air is minimal, so the sun’s rays are able to penetrate the Earth, creating dangerously high temperatures. This lack of humidity also accounts for deserts’ extreme temperature differences. Since moisture in the air is low, heat accumulated during the daylight hours dissipates quickly, causing temperatures to plummet once the sun goes down. Some deserts experience temperature differences as great as 50°F or more in a single day!
Deserts of the World
• North America: North American Desert
• South America: Atacama, Patagonian
• Africa: Sahara, Arabian, Namib, Kalahari
• Asia: Turkestan, Takla Makan, Gobi, Iranian, Indian
• Australia: Australian
Most of these deserts are separated further into regions, each with a specific name. The North American Desert is divided into four regions: the Sonoran, Mojave, Great Basin, and Chihuahuan.
Surviving in the Desert
Deserts are some of the most inhospitable places on Earth, but despite the callous, arid environment, some creatures have managed to eek out a way of life. Desert-dwelling plants and animals have astonishing adaptations that allow them to survive harsh desert conditions.
Desert Plant Adaptations
Every living organism on Earth requires some form of moisture in order to survive, and in deserts, this is the most limiting factor. Deserts get an extremely limited amount of precipitation each year, which makes supporting plant life an extreme challenge. There are two basic strategies plants use to deal with this ever-present dilemma: drought evasion or drought resistance.
The Drought Evaders: A Sit-and-Wait Strategy
Many plants have circumvented a lack of moisture by altering their life strategy to generate, unfold, and complete in the time span of a single rain event. Certain grasses and weeds avert drought by remaining in a dormant stage as a seed until the seasonal rains come. A tough seed coat prevents them from desiccation (drying out) while they lay dormant. These plants have a short life span and dedicate their meager existence to perpetuating the next generation of desert-dwellers.
The Drought Resistors: Moisture Misers
Other plants, like shrubs and bushes, have developed many creative strategies to work around the perpetual water shortage in the desert. Some, like the creosote bush, have shallow roots that spread just beneath the surface to absorb surface moisture from rain as well as deep tap roots that explore deeper soil layers for moisture. Some plants have sparsely distributed, waxy leaves and some even shed them, both in order to prevent transpiration (evaporation through the leaves). The paloverde (“green tree”) has a chlorophyll-laden stem, enabling photosynthesis to occur without the additional threat of water loss through leaves. Succulents, like cactuses, conserve water in their tissues and release it in limited amounts over long periods of time to nourish the plant; sharp spines and irritating hairs prevent other organisms from obtaining the precious fluid. An interesting plant known as the night-blooming cereus stores water in a specialized underground bulb-like structure.
Desert Animals: Extreme Survivors
While most desert plants survive the arid climate through modifications of their structure, many desert animals alter their behavior to cope with the stressors of desert life. The majority of desert denizens limit their periods of activity to the night, when temperatures are cooler. Amphibians, such as the spadefoot toad, aestivate (a form of summer hibernation) during the dry season, emerging only during the rainy season. There are many animals, however, that have special adaptations for surviving the desert heat. Jack rabbits, for example, have large, upright ears with large blood vessels; this allows blood traveling through the ears to be cooled by the wind and re-circulated throughout the body, cooling the rest of the blood. Reptiles have roughly-scaled skin to prevent water loss.
The Rainy Season- A Temporary Eden
Even the driest, hottest, most arid deserts in the world have to get rainfall at some point in order to sustain life, and when it rains, it pours! Once a year (or once every several years in some regions) the desert sky opens up and healing drops of liquid life rejuvenate the landscape. Almost overnight the desert transforms from a desolate wasteland to a thriving garden of lush vegetation. Dormant seeds germinate; bare branches extrude verdant, green leaves; fruits and flowers blossom in luxuriant radiance. For a few short weeks, the desert is a tropical paradise, and this is when all the action happens. Plants generate the seeds that will perpetuate the next generation of desert survivors, and animals gorge themselves on the abundant vegetative resources. Then, almost as suddenly as the rains appeared, the fruits of their labor begin to vanish. Leaves wither and crumble under the scorching sun; pools dry up; animals burrow underground; and desert life fades back to its melancholy dormancy.
Desert Fun Facts
- The Sahara Desert in northern Africa is the largest desert in the world, encompassing over 3.5 million square miles; that’s almost as large as all of America’s 50 states!
- The Gobi Desert, in Mongolia, is actually cold for most of the year.
- There are some deserts in the world that are adjacent to tropical rain forests! These deserts are bordered by mountains that block the rain from entering; this is called the rain shadow effect.
Links for Additional Information on Deserts
Written by Rob Nelson
Rob is an ecologist from the University of Hawaii. He is also an award winning filmmaker. As principle director of the Untamed Science productions his goal is to create videos and content that are both entertaining and educational. When he's not making science content, he races slalom kayaks and skydives.
View all posts by Rob Nelson →
Deserts cover about one fifth of the Earths surface and occur where rainfall is less than 50 cm/year. Although most deserts, such as the Sahara of North Africa and the deserts of the southwestern U.S., Mexico, and Australia, occur at low latitudes, another kind of desert, cold deserts, occur in the basin and range area of Utah and Nevada and in parts of western Asia. Most deserts have a considerable amount of specialized vegetation, as well as specialized vertebrate and invertebrate animals. Soils often have abundant nutrients because they need only water to become very productive and have little or no organic matter. Disturbances are common in the form of occasional fires or cold weather, and sudden, infrequent, but intense rains that cause flooding.
There are relatively few large mammals in deserts because most are not capable of storing sufficient water and withstanding the heat. Deserts often provide little shelter from the sun for large animals. The dominant animals of warm deserts are nonmammalian vertebrates, such as reptiles. Mammals are usually small, like the kangaroo mice of North American deserts.
Desert biomes can be classified according to several characteristics.
There are four major types of deserts:
Hot and Dry
Hot and Dry Desert The four major North American deserts of this type are the Chihuahuan, Sonoran, Mojave and Great Basin. Others outside the U.S. include the Southern Asian realm, Neotropical (South and Central America), Ethiopian (Africa) and Australian.
The seasons are generally warm throughout the year and very hot in the summer. The winters usually bring little rainfall. Temperatures exhibit daily extremes because the atmosphere contains little humidity to block the Suns rays. Desert surfaces receive a little more than twice the solar radiation received by humid regions and lose almost twice as much heat at night. Many mean annual temperatures range from 20-25° C. The extreme maximum ranges from 43.5-49° C. Minimum temperatures sometimes drop to -18° C.
Rainfall is usually very low and/or concentrated in short bursts between long rainless periods. Evaporation rates regularly exceed rainfall rates. Sometimes rain starts falling and evaporates before reaching the ground. Rainfall is lowest on the Atacama Desert of Chile, where it averages less than 1.5 cm. Some years are even rainless. Inland Sahara also receives less than 1.5 cm a year. Rainfall in American deserts is higheralmost 28 cm a year.
Soils are course-textured, shallow, rocky or gravely with good drainage and have no subsurface water. They are coarse because there is less chemical weathering. The finer dust and sand particles are blown elsewhere, leaving heavier pieces behind.
Canopy in most deserts is very rare. Plants are mainly ground-hugging shrubs and short woody trees. Leaves are replete (fully supported with nutrients) with water-conserving characteristics. They tend to be small, thick and covered with a thick cuticle (outer layer). In the cacti, the leaves are much-reduced (to spines) and photosynthetic activity is restricted to the stems. Some plants open their stomata (microscopic openings in the epidermis of leaves that allow for gas exchange) only at night when evaporation rates are lowest. These plants include: yuccas, ocotillo, turpentine bush, prickly pears, false mesquite, sotol, ephedras, agaves and brittlebush.
The animals include small nocturnal (active at night) carnivores. The dominant animals are burrowers and kangaroo rats. There are also insects, arachnids, reptiles and birds. The animals stay inactive in protected hideaways during the hot day and come out to forage at dusk, dawn or at night, when the desert is cooler.
Semiarid Desert The major deserts of this type include the sagebrush of Utah, Montana and Great Basin. They also include the Nearctic realm (North America, Newfoundland, Greenland, Russia, Europe and northern Asia).
The summers are moderately long and dry, and like hot deserts, the winters normally bring low concentrations of rainfall. Summer temperatures usually average between 21-27° C. It normally does not go above 38° C and evening temperatures are cool, at around 10° C. Cool nights help both plants and animals by reducing moisture loss from transpiration, sweating and breathing. Furthermore, condensation of dew caused by night cooling may equal or exceed the rainfall received by some deserts. As in the hot desert, rainfall is often very low and/or concentrated. The average rainfall ranges from 2-4 cm annually.
The soil can range from sandy and fine-textured to loose rock fragments, gravel or sand. It has a fairly low salt concentration, compared to deserts which receive a lot of rain (acquiring higher salt concentrations as a result). In areas such as mountain slopes, the soil is shallow, rocky or gravely with good drainage. In the upper bajada (lower slopes) they are coarse-textured, rocky, well-drained and partly laid by rock bench. In the lower bajada (bottom land) the soil is sandy and fine-textured, often with caliche hardpan. In each case there is no subsurface water.
The spiny nature of many plants in semiarid deserts provides protection in a hazardous environment. The large numbers of spines shade the surface enough to significantly reduce transpiration. The same may be true of the hairs on the woolly desert plants. Many plants have silvery or glossy leaves, allowing them to reflect more radiant energy. These plants often have an unfavorable odor or taste. Semiarid plants include: Creosote bush, bur sage (Franseria dumosa or F. deltoidea), white thorn, cat claw, mesquite, brittle bushes (Encelia farinosa), lyciums, and jujube.
During the day, insects move around twigs to stay on the shady side; jack rabbits follow the moving shadow of a cactus or shrub. Naturally, many animals find protection in underground burrows where they are insulated from both heat and aridity. These animals include mammals such as the kangaroo rats, rabbits, and skunks; insects like grasshoppers and ants; reptiles are represented by lizards and snakes; and birds such as burrowing owls and the California thrasher.
Coastal Desert These deserts occur in moderately cool to warm areas such as the Nearctic and Neotropical realm. A good example is the Atacama of Chile.
The cool winters of coastal deserts are followed by moderately long, warm summers. The average summer temperature ranges from 13-24° C; winter temperatures are 5° C or below. The maximum annual temperature is about 35° C and the minimum is about -4° C. In Chile, the temperature ranges from -2 to 5° C in July and 21-25° C in January.
The average rainfall measures 8-13 cm in many areas. The maximum annual precipitation over a long period of years has been 37 cm with a minimum of 5 cm.
The soil is fine-textured with a moderate salt content. It is fairly porous with good drainage. Some plants have extensive root systems close to the surface where they can take advantage of any rain showers. All of the plants with thick and fleshy leaves or stems can take in large quantities of water when it is available and store it for future use. In some plants, the surfaces are corrugated with longitudinal ridges and grooves. When water is available, the stem swells so that the grooves are shallow and the ridges far apart. As the water is used, the stem shrinks so that the grooves are deep and ridges close together. The plants living in this type of desert include the salt bush, buckwheat bush, black bush, rice grass, little leaf horsebrush, black sage, and chrysothamnus.
Some animals have specialized adaptations for dealing with the desert heat and lack of water. Some toads seal themselves in burrows with gelatinous secretions and remain inactive for eight or nine months until a heavy rain occurs. Amphibians that pass through larval stages have accelerated life cycles, which improves their chances of reaching maturity before the waters evaporate. Some insects lay eggs that remain dormant until the environmental conditions are suitable for hatching. The fairy shrimps also lay dormant eggs. Other animals include: insects, mammals (coyote and badger), amphibians (toads), birds (great horned owl, golden eagle and the bald eagle), and reptiles (lizards and snakes).
Cold Desert These deserts are characterized by cold winters with snowfall and high overall rainfall throughout the winter and occasionally over the summer. They occur in the Antarctic, Greenland and the Nearctic realm. They have short, moist, and moderately warm summers with fairly long, cold winters. The mean winter temperature is between -2 to 4° C and the mean summer temperature is between 21-26° C.
The winters receive quite a bit of snow. The mean annual precipitation ranges from 15-26 cm. Annual precipitation has reached a maximum of 46 cm and a minimum of 9 cm. The heaviest rainfall of the spring is usually in April or May. In some areas, rainfall can be heavy in autumn. The soil is heavy, silty, and salty. It contains alluvial fans where soil is relatively porous and drainage is good so that most of the salt has been leached out.
The plants are widely scattered. In areas of shad-scale, about 10 percent of the ground is covered, but in some areas of sagebush it approaches 85 percent. Plant heights vary between 15 cm and 122 cm. The main plants are deciduous, most having spiny leaves. Widely distributed animals are jack rabbits, kangaroo rats, kangaroo mice, pocket mice, grasshopper mice, and antelope ground squirrels. In areas like Utah, population density of these animals can range from 14-41 individuals per hectare. All except the jack rabbits are burrowers. The burrowing habit also applies to carnivores like the badger, kit fox, and coyote. Several lizards do some burrowing and moving of soil. Deer are found only in the winter.