Did you know deserts can be either hot deserts or cold deserts? Hot deserts are such like the Sahara desert in North Africa where there is little rainfall for an entire year. Cold deserts is where precipitation (rainfall) is mainly snow - but only ten inches or less per year such as the Great Bain are in the United States or the Gobi desert in Northern China. Deserts cover about one fifth of the Earth's surface and occur where rainfall is less than 50 cm/year.

Where are these deserts?

Deserts can be found in mainly two areas: the sub-tropical interior regions between 15º and 30º latitude and along the western coastlines of continents.

Deserts Regions

Deserts can be classified into several types based on certain charcteristics.They are Hot and Dry deserts, Semiarid, Deserts, Coastal Deserts and Cold Deserts.

• Hot and Dry deserts
  These are generally warm throughout the year and very hot in the summers with very little rainfall occuring in the winter. Daily temperatures are extreme because the atmosphere contains little humidity to block the Sun's rays. Desert surfaces receive almost twice the solar radiation received by humid regions and lose almost twice as much heat at night. 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 and evaporation rates regularly exceed rainfall rates. Sometimes rain starts falling and evaporates before reaching the ground. Soils are course-textured, shallow, rocky or gravely with good drainage and have no subsurface water. 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 have water-saving 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. 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 look for food at dusk, dawn or at night, when the desert is cooler.
  
  
• Semiarid Deserts
  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. 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. 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 the heat
  
  
• Coastal Deserts
  The Atacama of Chile is a good example of this . 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. Some animals have specialized adaptations for dealing with the desert heat and lack of water. Some toads seal themselves in burrows with specialsecretions and remain inactive for eight or nine months until a heavy rain occurs. Some insects lay eggs that remain dormant until the environmental conditions are suitable for hatching.
  
  
• Cold Deserts
  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 and Greenland. 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. The plants are widely scattered. 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.

Most desert plants are adapted to this harsh environment by being either drought or salt-tolerant. They store water in their leaves, roots, and stems. Some desert plants have long tap roots that burrow to the water table, anchor the soil, and control erosion. Desert vegetation is sparse but widely diverse and vaires according to the type of desert. Cacti are often seen as desert plants, because they have adapted well to the dry environment. Notice that instead of leaves they have the spines which actually helps to prevent water loss by evapouration. Cold deserts have grasses and shrubs as the dominant vegetation.

	Saguaro Cactus. Has a green stem, photosynthesis occurs in the top layer of the stem instead of in leaves. Another adaptation is its large network of roots which extend far away from its trunk whcih collects water after it rains. These roots also wrap about rocks providing anchorage from winds blowing across the desert. This is stored in the stem, keeping the saguaro alive until the next rain. Its fruit is used in jam and woody skeletons are used in building materials. Mainly gorws in the Southern Arizona region.
	Tumbleweed. Often seen in the wild wests looks like a skeleton of a normal shrub.Seeds are dispersed as it rolls along usually 250,000 seeds per plant. These Plants thrive in salty and alkaline soils. At some point in time they were used as hay and silage for livestock in Canada after a period of drought.
	Desert Lily. Mostly found on sandy desert flats and slopes. Usually blooms between March to May. The Desert Lily's leaves are about an inch wide with curved edges and grow 8 to 20 inches long. Native Americans used the bulb as a food source. These bulbs can remain in the ground for several years, waiting for enough moisture to emerge.

These animals have adapted both in behaviour and in physical structure at avoiding excess heat and excessive water loss. Staying undergound during the day or for long periods of time to avoid the desert sun or the eating of food that conatins some water is just a few examples of how some animals adapt.Reptiles, like snakes and lizards, have tough leathery skins to protect them. Desert animals get most of their liquid from the plants or insects they eat.

	Kangaroo Rats :These are pale in color with light variations of tan, cream and off-white. 9 to 14 inches is the average length.They mainly feed on grasses and seeds and can convert the seeds into water! An interesting adaptation is that they do not sweat nor pant like other animals to keep cool.In addition they have specialised kidneys which allows them to dispose of waste materials with very little output of water. Most Kangaroo Rats hop on their hind feet, using their tails for balance.
	El Lobo (Mexican Gray Wolf): Mexican Gray Wolf was declared an endangered species in 1976 they are the rarest of the world's wolves.They are believed to be ancestors of the domestic dog.Wolves eat a wide variety of food, including small animals like mice and squirrels, large animals like deer and moose and domestic animals life cows,sheep due to their defensless nature.
	Golden Eagle: They have large nests made of sticks in trees or cliff walls where they have a good view of the ground below. Golden Eagles are masters at soaring. With their large wingspan of up to 6- 7.5 ft they can soar for long periods of time with little wing flapping. They may catch rising masses of warm air, to carry them in a spiral fashion upward high into the sky. If the bird spots prey while soaring, it can tuck its wings and swoop at speeds up to 200 mph. If you are close enough, the bird may sound like a low-flying, small airplane. The birds may also hunt from a favorite perch.Their powerful eyesight allows them to find their prey easliy from up high .And by swooping in a sudden flash they catch their prey, gripping them in their beak or vice grip talons
	The Roadrunner: Can be found in the Mojave and Sonoran desert areas. Average size of a roadrunner is about 20 inches. Mainly feeds on insects, lizards, and rattlesnakes. They can live up to 7 or 8 years. The young are hatched from eggs. They secrete salt form their nasal passages and reabsorb water from their excrement.
	Desert Iguana : Mainly found in the Mojave and Sonoran desert regions. The can grow up to 10 to16 inches long with a large, round body and a long tail. It is colored brown around the head which diffuses into a reddish brown netlike pattern. It has tan or gray spots on the neck and trunk.. The tail is gray or white encircled with rows of dark spots. They often find a small bush to hide in to keep cool, if the temperature becomes ot hig they remian inactive.
	The SideWinder : A venomous snake, also called the "Horned Rattlesnake." It is unique because of its sideways form of movement with its body moving in an S-shaped curve. Average length 18 to 32 inches. Preys mostly on Kangaroo Rats, lizards and small birds. Rodents are bitten, released and tracked down, while lizards are held until the venom takes effect.
	Praying Mantis : Praying mantids get their name from the appearance of their front legs, which they hold in a "prayerlike" manner. "Mantid" derives from a Greek word meaning "prophet" or "seer." Size varies from one to three inches long, and they have a distinctive appearance. They feed on insects,and small birds and reptiles.Mantids grab their prey with the front legs which can quickly shoot out and grasp a victim. The mantid’s mouth is more grasshopper like; its small mandibles require that the insect eat live prey like a stalk of celery. Mantids feed upon a variety of insects, and they have even been known to capture and consume hummingbirds.

Ships of the Desert

Food Store:

The Arabian camel has one hump and the Bactrian camel has two humps. These humps store flesh and fat and can be absorbed into the body for food as necessary

Water Adaptation :

Camels can go without water and food for 5-7 days which is good for climates where the temperatures are very hot and a little water supply is sometimes difficult. They also perspire very little.

Physical Adaptations :

The camel can close its nostrils to protect against the harsh winds and its long eyelashes protects its eyes from the desert dust while the bushy eyebrows shades their eyes from the sun. The camels ears are lined on the inside with fur to filter dust coming into the ear canal. Hard calluses or skin on the joints (like the chest & knees) and thick pads on the feet protects the camel from the hot desert sand. Camels also have special , flat, broad leathery pads with two toes on each foot. As the camel walks on the sand the pads spread, preventing the feet from sinking into the sand.

• Bedouin in the Sahara
  
  They are know as the " people of the tent". They are naturalized Arabs descended from Ishmell. There maybe about 10 millions of them, spreading from their origins in Arabia to the arid regions of the Middle East. Some of them are camel raisers and drivers, sheep and goat nomads, cattle-driving nomads, merchants, artisan and entertainer castes. In general, they despite agricultural and manual labour, but there are still tribes settle in fertile areas near to oases and raise cereal crops, using camel dung as fuels.

• African Bushmen of the Kalahari
  
  The Bushmen of the Kalahari desert are the last of a group of nomadic people that once lived all over South Africa. They have yellow-brown skin and are generally short (about 150cm). They speak a language full of extraordinary clicking sounds. Most of them became herders or farmers, while some are still rather primitive, living a life of hunting and gathering with their naked bodies. They often coat theier bodies with oil and then cover it with dust to protect them fron the desert sun.

• Aborigines in Australia
  
  The indigenous people of Australia were Aborigines who lived off the land for thousands of years before the first white settlers arrived. They lived a nomadic life closest to nature, with least amount of material possessions among the desert peoples. They were hunter-gatherers. They formed into small and spread-out food-gathering groups and shared the animals and plants they found. The men carry the hunting weapons, spears, throwing sticks and boomerangs. The women would carry a few stone and bone tools and digging sticks which can be used as weapons.They had their own art, music, social functions like corroborees and some religious time. There is a musician storyteller in each tribe. The stories would be passes orally. Almost all Aborigines were naked. At night, they would gather around a campfire to keep them warm.