Why Are Deserts Hot?

Not all deserts are hot!

Because the definition of a desert is that it lacks moisture, a desert is not defined as being hot. For example, the Atacama Desert in Chile is considered the driest place on earth and it is rather cold for a desert, with daily temps from 32°F to 77°F (1). Some deserts are cold because of their altitude, some are cold because they are so far from the equator (polar deserts) and others are cold because of a dominant cold wind flow.

Here's a couple reasons why some deserts are hot:

1) Many deserts are largely influenced by something called a subtropical high pressure (described in How do deserts form?). Subtropical refers to it's location, out of the tropics. High pressure is an area of sinking air. As air sinks, it heats up. Not only that, but the warmer air will aid in evaporating water. So, Under a large area of high pressure that rarely moves, there is sinking air which warms the earth and evaporates water from the soil...perfect for a hot desert!

2) Sunlight energy can be used to evaporate water. If there is little to no water to evaporate, then all of that sunlight energy is absorbed by the earth. Then the earth emits more energy into the air thus heating the air even more.

3) The closer a desert is to the equator, the closer it is to the most intense sunshine all year long. The more intense the sunshine, the hotter the land and air will get.

Some Examples of Hot and Cold Deserts :

Hot Deserts

• Australian
• Arabian, Arabian Peninsula
• Mojave, US (Arizona, California, Nevada)
• Sahara, Northern Africa
• Sonoran, US (Arizona, California) & Mexico

Cold Deserts

• Atacama, Chile/Peru
• Gobi, Northern China/Southern Mongolia
• Great Basin, US (Idaho, Nevada, Oregon & Utah)
• Namib, Coasts of Southwestern Africa
• Turkestan, Parts of Middle East & Russia

Good work
Here is missing bold subtropical high pressure defined




In this map below you'll notice all the deserts in orange to reddish colors. Then, I have drawn a black line where 30 degrees North and 30 degrees South is located. Notice how many of the large deserts are all located in or around these belts. Again this is the location of the subtropical high pressure that helps to create atmospheric conditions ripe for desert formation.




Here's why these black lines above are ideal atmospheric conditions for deserts; the air from storms near the equator rises very high and eventually falls back down to earth creating the subtropical high pressure zone. This air in the subtropical high pressure zones is very dry because the air has dropped most of its moisture in the form of rain over the tropics. Also, as the air sinks around 30°North and 30°South it warms due to compressional heating. Warmer air encourages more evaporation from the surface which helps to further the dry climate. Along with a dominant high pressure system, there tends not to be any strong winds. Without a dominant wind blowing in storms or moisture off the ocean, the land further remains dry.

Did You Know: The region around 30° North and 30° South is called the horse latitudes. The name horse latitudes came about due to Spanish sailing ships headed for the West Indies. As the ships encountered the calm winds around 30° degrees North, the ships wouldn't move fast enough. So, sailors often threw horses overboard in order to preserve fresh water for themselves.

http://weathersavvy.com/Q-Climate_DesertsFormed.html