Desert rainfall and temperature

Typical of desert extremes are conditions in the Rub'al Khali, the "Empty Quarter", of southern Arabia. For most of the year there is only a trace of rain but over 30mm may fall on a single day in the winter. July temperatures may reach over 48C(120F),dropping to 15C(60F) at night, and December extremes range from 26 to 6.6C (79-20).

WATER

Water needs are paramount. Finding it is VITAL. If you have it, ration it immediately. If you are stranded by mechanical failure during a planned desert crossing, you will have plotted your route with an awareness of oases, wells and waterholes.

Wells can be very deep and the water level require a container lowered on a line to reach it. Small water holes in wadi bottoms are often seasonal. They are usually covered with a stone or brushwood. Away from known waterholes, try digging at the lowest point between dunes. Do not dig in the heat of the day, the exertion will use up too much fluid and you may not be able to replace it.

You must always balance fluid loss against possible gain. Exploit cactus and roots as water sources and , in deserts where the day/night temperature range is great, exploit this to produce water by condensation.

Desert Life expectancy

Life expectancy depends upon the water available and your ability to protect the body from exposure to the sun to minimize perspiration. Allow a slight negative balance. Drink 1.5 litre for every 2 litre lost and then drink at the rate the body is sweating.

Life expectancy depends upon the water available and your ability to protect the body from exposure to the sun to minimize perspiration. Allow a slight negative balance. Drink 1.5 litre for every 2 litre lost and then drink at the rate the body is sweating.

Efficiency is then impaired little and no water is wasted. Less fluid will not result in less sweating. Sweating is a cooling mechanism, not a way of losing moisture. If more fluid is drunk than needed it will be excreted and used to no purpose.

Without water you will last about two and a half days at 48C(120F) if you spend the whole time resting in the shade, though you could last as long as twelve days if the temperature stays below 21C(70F).

If you are forced to walk to safety the distance you cover will relate directly to water available. With none, a temperature of 48C(120F), walking only at night, resting all day, you could cover 40km(25miles). Attempting to walk by day you would be lucky to complete 8km(5miles) before collapse. At the same temperature, with about 2litres of water you might cover 56km(35miles) and last three days.

Your chances are not appreciably increased until available water reaches about 4.5 litres per person, though training and determination to survive could contradict predictions.