Desert Survival

By Edward J. Otten, MD

Deserts comprise about 15% of the earthís land area. Approximately 8% of the land area of the United States , or 300,000 square miles, is desert. Most of the American deserts are part of or adjacent to National Parks and Forests and are frequently visited. This includes Grand Canyon , Great Basin , Big Bend , Arches, Zion , Organ Pipe, and Joshua Tree, for example.

An area that has less than 10 inches (25 cm) of rain, unevenly distributed throughout the year, is considered desert. Most deserts are found between 30f South and 30f North latitude, making them hot as well as dry, such as the Sahara , Arabian, Australian, and Kalahan deserts. But there are several large areas of "cold" desertóthe Gobi, Great Basin, and Patagonianóthat are found beyond 40f North and South latitudes and have variable temperatures.

There are several climatic processes that produce desert areas. The most important of these are the six cells of air currents that descend at the poles and near the Tropic of Cancer and Tropic of Capricorn. These air currents, driven by the sun and the rotation of the earth, create areas of relatively warm, dry climate. The second important process is the problem of rain shadows caused by mountain ranges along the western edge of the continents. These areas lie to leeward of the prevailing winds and moist oceanic air is unable to rise over the mountains before it cools and loses its moisture on the western slopes. The dry air then rises over the mountain and descends to the land drying it. The Andes shadow the Patagonian Desert , the Sierra Nevada and Cascades shadow the Great Basin and Mojave, the Great Dividing Range in Australia places most of that continent in a rain shadow.

The dry land that is formed is unable to sustain a large amount of plant life. This lack of vegetation allows the sunís energy to directly heat the ground. The heat concentrates in the ground and in the air directly above it. In a non-desert forested region the plants give off moisture via transpiration; this phenomenon, along with the plants themselves, absorb most of the sunís energy before it can heat the ground. The large surface area of the vegetation also disperses the heat energy so the temperature on a forest floor rarely rises above 100f F (39f C). In deserts, the combination of solar radiation, high winds, and hot temperatures causes an increase in the evaporation of any moisture that does reach the ground. The same factors that cause a high temperature during the day allow for a rapid loss of heat during the night. Temperatures may vary 40 to 45f F in a single 24-hour period.

It would seem that this climate only would allow for a sparse flora and fauna. This is not the case. Death Valley, where air temperatures have been recorded at 134f F, has 600 species of plants, 30 species of mammals, 25 species of reptiles, and 2 species of fish. The plants and animals that have evolved in this environment have developed ingenious methods for adapting to the aridity and extremes of temperature. Man, in order to survive in the desert, must adopt some of the same methods used by the indigenous organisms.

Preparation for a Desert Climate

Obviously, the more prepared someone is for a particular climate the more likely he or she will survive, all other things being equal. Things are never equal, however, and luck is probably the most important, albeit the most uncontrollable, factor. There are several controllable factors, namely physical conditioning, clothing, survival kit, and survival skills may prevent needless deaths in the desert.

Physical conditioning and acclimatization is probably just as important with desert travel as with mountaineering. The bodyís need for water cannot be lessened by these methods, but the amount of electrolytes lost and the efficiency of the sweating apparatus can be optimized. Lower body strength may help to prevent a minor injury such as an ankle fracture that in the desert environment could be fatal if the injured person was unable to get help or water. Prior to a trip to the desert for the unacclimatized individual, I recommend a level of fitness at least equivalent to an aerobic workout to 80% of maximum heart rate for 30 minutes, 4 times a week.

Upon arriving in the desert area, the individual should spend at least 3 days acclimatizing before starting out on any long hikes (more than 5 miles). This will allow for the increased intake of water that may be up to 3 to 5 gallons per day and the adjustment to the lack of vegetation and increased solar radiation, and the large temperature variations. Most activity should take place between dawn and 10 A.M. and between 3 P.M. and dusk. Between 10 A.M. and 3 P.M. , the hottest time of the day, it is best to stay in the shade and sleep, read, or handle domestic duties.

The most important conditioning is mental conditioning or "the will to survive." Throughout the survival literature this is constantly cited as the one thing that brought survivors through their ordeals. Unfortunately, this cannot be taught. However, the potential is in all of us but may only appear in extreme circumstances. Many medical personnel develop a sense of aequanimitas or coolness under fire when dealing with emergencies on a daily basis. Jet pilots seem to have a similar trait. While the will to survive is not exactly the same as this, it may arise in unlikely individuals, just like courage in a battle.

The clothing most suitable for the desert is similar to that worn in most wilderness areas, only the type of material may be different. Polypropylene, wool, pile, and Gore-TexÆ are the choices of the mountaineer whose enemy is hypothermia. While hypothermia is a possibility on the desert, hyperthermia and dehydration are more likely. Ripstop cotton is ideal due to its evaporative ability, and long- sleeve shirts and trousers made from this material are excellent for desert conditions. A light color should be chosen to help reflect solar radiation. A pile jacket or wool sweater is needed at night in many desert areas. Most novices traveling in the desert remark on how cold it is at night and how ill prepared they were for it.

A rule of thumb is "expose as little skin as possible." The skin must be protected from heat, ultraviolet rays, blowing sand, insects, and water loss. A hat is an absolute necessity and should be broad brimmed or a kepi to protect the neck and face. A cravat or large handkerchief can be used as an emergency hat, if the other is lost. It can also be used as a towel or soaked in water and placed between the head and the hat to act as a solar air conditioner. Sunscreen and a lip balm with sunscreen should be used frequently to protect exposed skin. Sunglasses or goggles are needed to protect the eyes. Ultraviolet keratitis similar to snowblindness can occur especially at higher elevations. Corneal abrasions from blowing sand are quite common and preventable.

Leather gloves protect the hands from hot objects as well as cactus spines and thorns. Footwear can be leather or manmade materials and should be ankle high or higher. Low-cut shoes will allow sand to enter and do not give adequate ankle support. Jungle boots with metal spike protection and running shoes may get extremely hot in the desert soil and are not a good choice for desert travel. Polypropylene (with or without wool) socks seem to decrease the amount of blistering and give adequate cushioning and insulation to the feet.

Survival Kit

The survival kit should have the necessary equipment and supplies to help you survive yet be small enough to be carried with you wherever you hike in the desert. The principle component should be water or the means of acquiring it. Unfortunately, water weighs 8 pounds to the gallon and this limits the amount that an individual can carry to about 1-day's supply. A solar still should be carried along with water purifying tablets or iodine. The best way out of a survival situation is to be rescued; therefore, signaling equipment is essential. Survival kit items should be selected that have multiple uses and they must be of high quality. Do not spare expense in purchasing equipment that your life may depend on.

Below is an example of a basic kit that may be carried in a relatively small pack:

 Basic Survival Kit

Nylon canteen, 5 qt.
Penlight
Canteen cup
Space blanket
Clear plastic sheet
Sunscreen
Plastic tubing
Signal mirror
Iodine crystals
Whistle
Band-Aids
several Sunglasses
Swiss Army knife
Parachute cord, 50í
W aterproof matchbox
Compass
Insect repellant
Hard candy
Safety pins
Needle and thread

When weight is not a consideration

the following items should also be carried:

Plastic water container, 5 gal/person
Folding shovel
Toilet paper
First aid kit
Nylon tarp
Gloves
Extra clothing
Food
CB radio

Necessity being the mother of invention, many items from vehicles can be used in an emergency; the rearview mirror can be used to signal, the hubcaps to collect water, batteries to start fires, and oil to produce smudge for signaling, to mention just a few.

The best survival kit is of no use if the person carrying it does not have the skills to use it correctly. These skills must be learned and practiced regularly or they will be lost. Until you have actually built a solar still you cannot anticipate the problems encountered. An experienced person can produce a solar still in 15 minutes. An amateur will take 60 minutes and lose more sweat than the still will produce in a week. Direction finding, fire building, shelter construction, and signaling are all necessary skills that must be learned before getting into a situation where your life may depend on them. It is too late to learn to swim after you have fallen out of the boat.

Priorities in a survival situation are based on the "rule of 3s," you can live

3 minutes without oxygen, 3 hours without warmth, 3 days without water,

and 3 weeks without food.

Assuming that there are no immediate medical problems or environmental hazards (i.e., fractured pelvis, landslide, flash flood, etc.) the top priority in a desert survival situation will probably be water.

If there is a limited amount of water available, then food should not be eaten unless the food contains a large amount of water. The metabolism of food and excretion of waste products requires unnecessary usage of water. Water obtained from lakes, streams, wells, or springs should be considered contaminated and purified before drinking. Water may sometimes be found by digging at the outside bend of a dry riverbed or stream. Vomiting and diarrhea caused by contaminated water could be quickly fatal in the desert. Rainwater, dew, and water obtained from solar or vegetable stills are relatively pure. Urine, seawater, or brackish water should never be drunk in a survival situation. Liquid from radiators is contaminated by glycols and should never be drunk. Many plants (such as barrel cactus and travelerís tree) and animals (such as the desert tortoise) contain water and can be used in an emergency.

A solar still can be made by stretching a 5í x 5í piece of clear plastic over a hole dug in the ground into which vegetation, urine, or brackish water has been placed. The sun will cause water to evaporate and collect on the underside of the plastic and then drip back into a container at the bottom of the hole. A tube can be used to remove the water from the container without dismantling the still. The amount of water produced will depend on the amount of moisture in the hole; bone dry sand will not be very productive. Build the still at night to conserve water. Dew, rainwater, and edible animals may also be collected in the still as a bonus.

Shelter

Shelter is essential if the effects of the sun during the midday are to be ameliorated. The temperature in the desert will vary both above and below the ground. The temperature at the ground surface will be the highest. It will decrease as one goes above or below the ground. Therefore, a shelter that protects from direct solar rays and has within it either a trench 12" to 18" deep or a platform 12" to18" high will be cooler than one in which you must be in contact with the ground. A second roof suspended 12 to18" above the first will trap a layer of air and decrease the temperature within the shelter. Metal vehicles will be like ovens, and it is better to sit on a seat cushion in the shade of an automobile or under the wing of an airplane than to be inside. Try to build the shelter in the shadow of a cactus, tree, or large rock. Avoid dry stream beds (arroyo, wadi, or dry wash) that could turn into a killer flood in a matter of minutes after a cloudburst miles away. Desert animals will seek out shelter during the day also and may venture into your shade. Reptiles may be venomous and mammals may carry diseases such as rabies or plague. Most of them can be scared off with a stick or rock.

Waiting for rescue or trying to find civilization

One of the earliest decisions that you will have to make is whether to wait for rescue or to attempt to find your way back to civilization. You need to look at all the factors that may decide your survival. What is the chance that you will be rescued? If you filed an itinerary or flight plan, if you have signaling equipment, a radio or emergency locator transmitter, water, shelter, and food, then you probably should stay where you are.

Your chances for rescue will be much better if you are near an object such as an airplane or automobile that can be seen by search and rescue (SAR) personnel. If you do decide to travel, mark a large arrow on the ground in the direction of travel and leave a note stating your direction of travel and plans. Travel in the cool of the night to conserve water, although the footing may be more hazardous. Before traveling in the desert or anywhere, obtain an up-to-date topographic map of the area and learn how to use a compass. Memorize major physical and manmade features so if you get lost without your map and compass, you will still be able to find a road, river, or power line that may lead to help. Direction can be approximated by using the shadow-tip method (using the movement of a shadow around noontime), a watch during the day, or the stars at night.

Signaling can best be accomplished during the day using a mirror and reflecting the sun off the mirror towards the horizon in the direction of potential help. If an aircraft is spotted, do not shine the mirror directly on the aircraft, but rather alternate flashing the mirror from the ground to the aircraft. A signal such as this can be seen at 30,000 feet. At night, a fire or penlight can also be seen at great distances if shone from a high point . A mirror cannot be "used up" but penlight batteries and firewood can, so wait until you hear the sound of an aircraft or rescuers before signaling by these methods.

Nature is neutral, neither for us nor against us. The game of survival, like all games of life, is based on our control of nature to the extent that we need to survive. This includes the nature inside of us, as well as outside of us. The first step in any survival situation is to gain control of ourselves, then to try to control those things outside ourselves such as climate and terrain.

 

Bibliography

Adolph EF. Physiology of man in the desert. New York : Hafner Press, 1969.

Craighead FC and Craighead JJ. How to survive on land and sea, 4th ed.

Annapolis, MD: Naval Institute Press, 1984.

MacMahon JA. Deserts. New York: Alfred Knopf, 1985.

U.S. Air Force Publication AFM 64-3, Survival training edition. Washington, DC,

Headquarters Dept of the Air Force, 1969.

U.S. Army Publication FM21-76 Survival. Washington , DC , Headquarters Dept of the Army, 1986.

Wagner FH. Wildlife of the deserts. New York: Harry Abrams, 1984.

Mel is a past president of the Wilderness Medical Society and the Director, Division of Toxicology and Professor of Emergency Medicine and Pediatrics, University of Cincinnati College of Medicine, Cincinnati, OH, USA.

Wilderness Medicine Letter, Volume 17, Number 2, Spring 2000