What is a Desert?

The world's Deserts present one of the most hostile environments for humans on the planet. Although popularly associated with very hot climates many deserts are not located in such places. The definition of a desert is an area that receives almost no precipitation (Rain, snow, moisture), with an annual precipitation of no greater than 25cm in a given year, other definitions list them as places where more moisture is lost from evaporation than falls as precipitation. Surprisingly the world’s largest deserts are Antarctica and the Artic with the best known and largest of the Hot deserts the Sahara coming third in size (see Arctic Survival article). The polar deserts have similar features to hot deserts but with any precipitation falling as snow. Antarctica even has some dry valleys where snow almost never falls and ice covered saline lakes indicating a higher rate of evaporation than snow fall,  possibly due to the effect of Katabatic winds which are able to evaporate ice.

The world’s top ten deserts are listed below in size order
Antarctic
Arctic
Sahara
Arabian
Gobi
Kalahari
Patagonian
Great Victoria Desert
Syrian Desert

Navigation and movement

Most deserts are featureless (or have repeating patterns of sand dunes) making navigation by landscape features difficult, lack of cloud cover does mean that navigation by the stars at night is possible if you are skilled and this can be useful as travelling at night if possible is the best way to conserve water and avoid heat in hot deserts. Contrary to the image portrayed in film sand covers only about 1/5th of the world’s deserts although sand seas and vast dunes are present in some and make walking draining and the use of vehicles difficult.  Rocky deserts are more common and by there very nature most deserts are barren, salt plans are also present in some due to intense evaporation.

Desert Flora/ Fauna

Deserts have virtually no vegetation and any species of plants present are highly adapted to arid environments and provide almost no shade or protection. Despite this considerable biodiversity can be found in deserts, the majority of animals are nocturnal and remain hidden underground during the day to conserve water and regulate body temperature. Adapted desert animals include coyotes, kangaroo rats, jack rabbits and other similar species throughout the world, hard to track and locate many can be used as a source of protein if caught and eaten. Common desert adaptations include modified kidneys to conserve water and cope with high salt contents, membranes and eye lashes to protect eyes against wind and sand grains, wide or heavily padded feet to protect against sharp stones and hot desert sand. A wide variety of insects and reptiles can also be found but many of these are poisonous either to eat or have poisonous bites or stings, by themselves the venom is rarely lethal but add to it the complications of dehydration and limited access to medical assistance they become a greater threat to life. In fact deaths by caused by animals are no higher than in other areas such as rain forests or savannah.  One issue to be aware of is scorpions especially when choosing a camp site. Scorpions are very well adapted to desert environments and have a tendency to lurk in footwear so it is important to make sure that footwear is hung upside down or checked in the morning before putting on. 

Desert plants are also well adapted being both drought and salt tolerant, many species store water in their leaves or roots and some fluid can be harvested from them if lucky.  Many Desert plants have extremely long tap roots to gather water from a greater area and these tough roots can be a source of fibre for making ropes/ strings. Others have spiky leaves to protect them not from herbivores but from high winds carrying abrasive sand and rock particles. The hostile environment means that many desert plans are very long lived and slow growing but adapted to react rapidly to infrequent rain for reproduction.
 
Environmental Hazards

The environmental hazards of cold deserts are dealt with under the arctic survival article here I will focus on the environmental hazards of hot deserts. Hot deserts have high daytime temperatures and low night time temperatures as the lack of humidity means the ground cools quicker as well as little or no cloud cover. Hot deserts are some of the hottest places on earth some reaching above 45 °C/113 °F in the day and dropping to nearly freezing point at night. A dry desert is unable to block sunlight or trap heat in plants or water so the solar radition reaches the ground unhindered.

Finding some kind of shade and keeping cool is vital to survival in a desert as the hotter you are the more you sweat as the body tries to cool itself this means you are loosing water and salts. Unless you really have to move the best plan is to stay put and wait rescue as you will be able to conserve energy, and fluid. To best conserve your resources find shade and place something underneath you as this will help prevent the hot ground affecting your body tempreture by conduction, keeping still will reduce the need to sweat. Try to eat sparingly as humans use water to aid digestion.

Don’t shed clothing as it will protect you from sunburn which will further rapidly dehydrate you and allow you to conserve your sweat, by trapping it against your skin and gaining the maximum benefit of its cooling effect. Wrapping clothes around your head will trap sweat from your hair and further protect you (there is a reason why desert people wear head scarves)

Careful control of what water you have is key. Regular sips are better than having to go a long time between drinks after drinking heavily. Try not to think about drinking as this will make you thirstier and don’t use thirst as an indicator to drink, distract yourself from thinking about your thirst, use non physical tasks such as children’s games like eye spy or word games to keep your mind off your thirst. Some sources suggest that you should drink no more than a litre of water every hour if the temperature is above 38C and half this amount if its below but this may seem a great deal of water but without this amount you risk heatstroke. Consider that any form of physical exercise will increase the amount of water needed. Even if you think you have enough water to travel to safety think about how much this will weight, a litre of water weights around 1 kg so a few days water in a hot desert can weight a lot. Your urine colour is a good indication of your hydration level with a dark colour an indication of dehydration.   Heat and dehydration are the big killers, heat exhaustion is the most common problem caused by loss of salts and fluid, signs of this include weakness, headaches, pale clammy skin and mental confusion.  Heat stroke has the same causes but will be fatal if not dealt with quickly, symptoms are normally a hot dry skin (unlike heat exhaustion) but also headache, vomiting and a fast pulse rate, a confused mental state normally precedes unconsciousness and death. Heat cramps are a result of loss of salt (hence the use of salt tablets) and are muscle cramps which start in the limbs and can spread throughout the body eventually preventing any physical activity.

Although rare deserts do get violent rain storms these can lead to flash floods with dry river beds and Wadis quickly filling making them hazardous. Some large rivers cross deserts such as the Nile but these are fed by headwaters in mountain ranges, other deserts have underground streams, sometimes plants have adapted deep roots to tap these and vegetation can be a sign of underground water. Some native peoples have developed other ways to obtain water either from sources stored in plants (but they rarely contain actual water despite the film image), the Bedouin have been known to under stones to collect the dew that forms on them before dawn. One trick involves a plastic bottle or container which you half bury in the ground, this simple method uses condensation to collect a small but useful amount of water.

Another environmental hazard is sandstorms. Sandstorms can last days and make navigation and travel extremely difficult they also clog vehicle filters and sand gets into equipment doing damage to everything from vehicles to communications equipment.  Hot deserts have fine particulate matter in the air and from personnel experience it is surprising how it can affect your respiratory systems, the best way to keep a scarf  or a piece of cloth over your mouth and nose,  during a Sandstorm this is much worse and goggles are needed to protect your eyes. If travelling the Sandstorm will be very disorientating so one tactic is to lie down and mark your direction of travel until the storm abates.

In summary the biggest issue for survival in a desert will be water and heat, without conserving water you will die quickly whereas lack of food can be tolerated much longer. As stated earlier the best option if stranded is to stay put and wait it out, using scrub to make a signal fire or a mirror to reflect unless you know there is little chance of rescue.

Recommended Reading

Deserts: A Very Short Introduction , Nick Middleton, An interesting book looking at the huge diversity found in deserts from the landscapes to the native peoples and wildlife, chapters are included on desert peoples, climate, wildlife, landscapes and the role of deserts in world climate. Also includes maps and illustrations/ photographs.

Deserts of the Earth: Extraordinary Images of Extreme , Michael Martin & Michael Asher, A stunning book filled with amazing images of desert environments, contains considerable text and information about these beautiful places. A photographic tour of some of the world’s great deserts with accompanying text from the author, who travelled these by motorbike, includes the Kalahari and the Great Sandy Desert.