Characteristics of Tropical Deserts

The Sahara is the world's largest tropical desert.

Tropical deserts are both the driest and hottest places on Earth. In fact, the world's highest recorded temperature, 136 degrees Fahrenheit, occurred in a tropical desert in Libya. The tropical desert is among the major climate types in the Köppen classification system, designated by BWh. A "B" climate type features little rain and a large daily temperature range, the "W" indicates that the lack of precipitation is so extreme as to form a desert and the "h" denotes an average annual temperature greater than 64 degrees Fahrenheit.

Geographical Distribution

Tropical deserts cover approximately 12 percent of the world's entire land surface. They are found at low latitudes just to the north and south of the equator, generally between 15 and 28 degrees latitude in both hemispheres. Most tropical deserts tend to lie inland and away from major bodies of water, although there are a few exceptions. The largest and most famous tropical desert is the Sahara of North Africa, but tropical deserts also can be found in southern Africa, the Middle East, western India, central and western Australia, Argentina, Baja California and northern Mexico.

Contributing Factors

Subtropical, high-pressure systems dominate the climates of tropical deserts, with their sinking air inhibiting precipitation and warding off any moist air masses. Lack of wind encourages any water to rapidly evaporate. Deserts near oceans, such as Baja California, are located in spots where cool, offshore currents suppress shower and thunderstorm formation.

Temperature Extremes

Possessing the highest mean annual temperatures of any climate in the world, tropical deserts' combined daytime highs and overnight lows can average as high as mid-90 degrees Fahrenheit. Constant sunshine and high sun angles unite to produce excessive heat. The most extreme high temperatures occur in deserts lying at the lowest elevations. Although tropical deserts are the hottest places on the planet overall, nights can become chilly. Once the sun goes down, the lack of clouds allows heat to easily escape into the upper atmosphere, drastically cooling the air at the surface. Hence, tropical deserts experience a significant fluctuation in daytime and nighttime temperatures.

Low Humidity and Precipitation

Relative humidity in tropical deserts hovers around 10 percent or less. On average, tropical deserts receive less than 10 inches of rain per year. An entire year's worth of rain can fall in a single day, and some years no precipitation occurs whatsoever. Additionally, tropical deserts receive the greatest percentage of sunshine of any location on Earth.

References

• Weather Explained: Temperature Extremes, Highest
• Blue Planet Biomes: World Climates
• Encyclopedia Britannica: Tropical and Subtropical Desert Climate
• Encyclopedia Britannica: Facts about Desert - Climate
• University of Wisconsin Stephen's Point: Tropical Desert Climate
• University of Wisconsin Stephen's Point: Tropical Desert Climate (BWh)