We all know that deserts are the hottest places on Earth, but what makes them different from other parts of the world?
We all know that deserts are the hottest places on Earth.
That is not necessarily true. What is true is that the hottest places on Earth are in deserts. Note the reversal. Much of the Arctic and Antarctic are technically deserts due to extremely low precipitation. Excluding these polar deserts, some deserts are quite cool, even if they are close to the equator. For example, Arica, Chile (the driest inhabited locale in the world), has a rather mild climate temperature-wise, despite being at 18°29′ south latitude. This is the case for much of the Atacama desert.
What makes them different from other parts of the world?
I'm assuming you are asking about those deserts that are hot in the summertime rather than deserts in general. A key ingredient for extremely high temperatures is a desert, but not a high latitude desert, high altitude desert, or coastal desert.
Very low precipitation is what distinguishes desert from non-desert biomes. Lack of precipitation is not sufficient for very high temperatures, as exhibited by the very cold polar deserts and the rather cool deserts that are well outside polar areas. Much of the Atacama is at a high altitude, as are the Gobi in China and Mongolia, the Taklamakan in China, and the high desert in the Mexico and the US. While some of these deserts can be hot during summer, they aren't ridiculously hot. Areas along the coast of the previously mentioned Atacama desert and the Namib in Africa are kept somewhat cool by ocean breezes. These coastal deserts can be uniformly mild year-round.
What is needed to create the possibility for extremely high temperatures is a desert that is not at extreme latitudes, that is well removed from coastal cooling, and that is at low altitudes. A desert is needed so as to receive the full brunt of solar radiation. Equatorial regions don't work because they tend to be cloudy and rainy. High latitude areas don't work because they don't receive very much insolation. High altitude areas don't work because temperature tends to decrease with increased altitude.
A low altitude desert in the horse latitudes is exactly what is needed, and this is why Furnace Creek in Death Valley, California (supposedly the hottest place in the world) and Tirat Zvi, Isreal (supposedly the hottest place in Asia) can be very, very hot. The horse latitudes are where the Hadley cell and mid latitude cell converge, creating long-lived high pressure areas where rain is highly unlikely. Most of the world's non-polar deserts are in or near the horse latitudes.
Even better than Furnace Creek are those areas that are so ridiculously hot that nobody sane would live there and hence there are no weather stations. We don't know, for example, how hot it gets in the Lut desert in Iran. It's too hot there for people to fathom, and is almost certainly hotter than is Furnace Creek.
The first thing to note is that not all deserts are hot - think Tibet. But there is no doubt that most deserts are distributed adjacent to the hot and wet climatic equator. This is no coincidence. Because the sun is at or close to being overhead in the equatorial zone, this belt receives the most solar energy per square metre. Hot air rises, dumping a lot of the moisture as it cools (hence tropical rain forests), then the air spreads out polewards in both north and south directions, flowing in the upper troposphere. Pressure distribution is such that this part of the global circulation is balanced by a return air flow close to ground level. Together this convective air circulation occurs in 'Hadley Cells' which constitutes the world's biggest heat re-distribution mechanism. The downflow part of the cells is where hot dry air descends under clear skies, and hence is where deserts occur.
Hot deserts are usually in a location where several factors are all occurring together:
- the elevation is near sea level (this ensures enough atmospheric heating)
- the latitude is not near the poles (not enough sunlight)
- the location is not in the path of any seasonal rainstorms (e.g. in the rain shadow of mountain ranges: rain clouds predominantly come from one direction and orographic rainfall occurs on only one side of the range )
Furthermore, you can read here:
Deserts are formed by weathering processes as large variations in temperature between day and night put strains on the rocks which consequently break in pieces. Although rain seldom occurs in deserts, there are occasional downpours that can result in flash floods. Rain falling on hot rocks can cause them to shatter and the resulting fragments and rubble strewn over the desert floor is further eroded by the wind. This picks up particles of sand and dust and wafts them aloft in sand or dust storms. Wind-blown sand grains striking any solid object in their path can abrade the surface. Rocks are smoothed down, and the wind sorts sand into uniform deposits. The grains end up as level sheets of sand or are piled high in billowing sand dunes. Other deserts are flat, stony plains where all the fine material has been blown away and the surface consists of a mosaic of smooth stones. These areas are known as desert pavements and little further erosion takes place. Other desert features include rock outcrops, exposed bedrock and clays once deposited by flowing water. Temporary lakes may form and salt pans may be left when waters evaporate. There may be underground sources of water in the form of springs and seepages from aquifers. Where these are found, oases can occur.