What Makes Deserts Hot?
Areas with average annual rainfall less than one hundred millimeters per year are classified as deserts. They make up approximately one-third of the surface of the earth. Hot deserts are classified by high daytime temperatures and low nighttime temperatures. Examples of hot deserts include the Arabian desert, the Kalahari and the Thar desert.
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Geographical Location
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According to "The Environment: Principles and Applications," hot deserts are commonly found in two geographical belts above and below the equator: between 30 degrees latitude north of the equator (belt one is 30 degrees north to 0 degrees equator) and 30 degrees latitude south of the equator (belt two is 0 degrees equator to 30 degrees south of the equator). These areas are characterized by high temperatures (higher than 25 degrees) due to the angle of sunlight, which falls directly over the equator and bends slightly in areas lying slightly above and below it.
High Rate of Evaporation
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In deserts, the rate of evaporation is higher than the rate of precipitation. Evaporation is the process in which water is converted from its liquid state to water vapor. The rate at which water evaporates depends upon the humidity level, temperature and wind speed. Precipitation occurs when clouds can no longer bear the weight of water. Those suspended particles of vapor fall on the ground as precipitation (snow, sleet, freezing rain, rain and hail).
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High Pressure
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Deserts are areas of high atmospheric pressure. This pressure prevents the formation of clouds, the absence of which provides the overhead sun direct, uninterrupted access to the desert. High pressure belts (also called horse latitudes) are located between 30 degrees latitude (north of the equator) and 30 degrees latitude (south of the equator). These high pressure zones give rise to high temperatures due to their nearness to the equator and the weather pattern of the wind. Cold air descends in high pressure zones, becoming warm as it nears the ground. There, instead of releasing precipitation (in the form of rain), ground heat evaporates the water before it can be released.
Limited Plant Life
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Lack of plant life also contributes to the heat of the desert. Trees and plants can reduce temperature by three to eight degrees, according to "Planning for Forest Resources and Biodiversity Management." Desert plants are mainly short woody trees or low-lying shrubs that are ineffective in providing an appropriate shade canopy. Examples of plants that are common to hot deserts include prickly pears, ocotillo, yuccas, ephedras and mesquite.
Low Humidity
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Hot deserts have low humidity. According to "Climate -- Vegetation: Afro-Asian Mediterranean and Red Sea Coastal Lands," low humidity allows at least 90 percent of the heat of the sun to reach the ground. This characteristic low humidly makes deserts heat up and cool down (during the nights) fairly quickly.
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References
- Climate -- Vegetation: Afro-Asian Mediterranean and Red Sea Coastal Lands; MA Zahran, Francis Gilbert; 2010
- Michigan Technological University: Evaporation
- Thurston High School, Springfield, Oregon: Desert
- The Environment: Principles and Applications; Chris C. Park; 2001
- University of Berkeley: The Desert Biome
- Photo Credit desert plants image by Carol Tomalty from Fotolia.com
