What the desert actually asks of you

The first thing the desert does is contradict the brochure. It is not uniformly hot: the Sahara at three in the morning is cold enough that you will wear every item of clothing you brought and still sleep badly. The Gobi drops below minus thirty in winter and sometimes gets snow on its dunes. Antarctica, which receives so little precipitation that it qualifies as a desert, is the largest one on Earth.

The second thing it does is remove the margin for error that you are used to. Everything else follows from that.

Understand which desert you are going to

"Desert" describes rainfall, not temperature, and the practical differences are enormous.

• Hot sand deserts - the Sahara, parts of Arabia, the Namib. Extreme daytime heat, sharp night-time cooling, and genuine navigation difficulty.
• High cold deserts - the Gobi, the Atacama, the Pamirs. Altitude compounds everything, and the Atacama has weather stations that have never recorded rain.
• Rocky and semi-arid - Wadi Rum, much of the American Southwest, the Kalahari, which gets enough rain to support grass and trees and is technically a savanna.
• Polar deserts - the McMurdo Dry Valleys, stripped bare by katabatic winds and unrained-on for roughly two million years.

The kit and the risks differ substantially. Read about the specific place, not about deserts.

Water: the arithmetic

In serious heat, an active adult can lose several litres a day through sweat and breathing, and you will not feel thirsty in proportion to the loss because dry air evaporates sweat before you notice it. The standard guidance for desert hiking is at least four litres per person per day, more if you are exerting yourself, and that is drinking water alone.

Practical rules: drink steadily rather than in large amounts occasionally; add electrolytes, because water alone flushes salt and can make things worse; and never rely on a single container. Carry water in at least two vessels so that one failure is an inconvenience rather than an emergency.

Heat, and the hours you simply do not use

Desert cultures organised themselves around this centuries ago and they were right. The middle of the day is for shade. Move early - first light to about ten - and again from late afternoon. Between those, do nothing energetic.

Cover up rather than strip off. Loose, long, light-coloured clothing reduces both heat load and water loss far better than bare skin, which is why the traditional dress across the Sahara and Arabia looks the way it does. Add a wide brim or a head wrap, and sunglasses that actually block UV, because reflected glare off pale sand is punishing.

Learn the early signs of heat exhaustion - heavy sweating, weakness, nausea, headache, clammy skin - and treat them by stopping, shading and rehydrating. Heat stroke, where sweating stops and confusion begins, is a medical emergency.

Cold, which is the part people fail to plan for

Clear desert skies radiate heat away extraordinarily fast after sunset. A 40°C day can become a 5°C night, and at altitude it goes below freezing. Every experienced desert traveller carries an insulating layer they did not appear to need at midday.

Pack a warm mid-layer, a hat, and a sleeping bag rated colder than the forecast suggests. If you are on an organised camp, ask what the overnight low actually is rather than assuming.

Navigation and the things that go wrong

Sand deserts lack landmarks by definition, dunes change shape, and tracks disappear. A phone is not a navigation system when it is at 8% and 48°C.

• Carry offline maps and a paper map, and know roughly where north is without a device.
• Tell somebody your route and your expected return time, and stick to it.
• If you are driving, travel in two vehicles or with a guide. Recovery gear, a compressor, and knowledge of how to lower tyre pressure for soft sand are not optional extras.
• If a vehicle breaks down, stay with it. It is visible, it provides shade, and it holds your water. Walking away from a vehicle is the classic fatal decision.
• Sandstorms reduce visibility to a few metres in minutes. Stop, shelter, cover your face, and wait. They pass.

Hire a local guide, and not only for safety

In most desert regions, a guide is the difference between a landscape and a place. They know where the water is, which track is passable this month, when the wind gets up, and where you can sleep out of it. They also know the things you would never find: the rock paintings in Tassili showing swimmers and hippos, proof the Sahara was green within the last 10,000 years; which dunes boom when the sand avalanches; where the salt caravan still passes.

It is also, straightforwardly, where the money should go. Desert communities have very few economic options, and guiding is one of the good ones.

What to carry, specifically

• Water, in more than one container, plus electrolyte tablets.
• Long, loose, light clothing; a head covering; UV sunglasses; high-factor sunscreen and lip balm.
• A warm layer and a hat for the night.
• A head torch with spare batteries.
• Offline maps, a paper map, a compass, and a power bank.
• A small first-aid kit including rehydration salts and blister treatment.
• Something to keep sand out of your camera. It gets everywhere and it does not leave - two months later you will find Saharan sand in the spine of a paperback.

Why go at all

Because the silence is not like other silences. After the generator goes off in Wadi Rum there is no sound at all - not wind, not insects, nothing - and six people will sit in the dark for an hour without speaking. Because the Milky Way in the Kalahari is bright enough to cast a shadow. Because at Deadvlei the camelthorn trees died nine hundred years ago and the air is too dry for them to rot, so they simply stand there, black against white clay, waiting.

The desert asks for preparation and gives back scale. It is a fair trade.