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Tropical and subtropical desert climate
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What is a desert climate?
A tropical and subtropical desert climate, a major climate classification in the Köppen system, is influenced year-round by subtropical anticyclones, resulting in descending air, strong inversions, and clear skies that inhibit precipitation.
These true desert (BW) climates typically lie between 15° and 30° latitude at the poleward end of the Hadley cell circulation. The most arid zones are far from moisture-bearing winds and are most developed on continents' western sides, where subtropical anticyclones are most intense.
Cloud cover is uncommon, and precipitation ranges from 0 to 25 cm annually. Temperature variations are extreme, with monthly means between 21–32 °C (70–90 °F). Daily temperature ranges of 35 °C (63 °F) are not unusual.
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Where are tropical and subtropical desert climates usually found?
Tropical and subtropical desert climates are typically located between 15° and 30° latitude, within the subtropical anticyclone region, at the poleward end of the Hadley cell circulation. These areas are characterized by descending air, elevated inversions, and clear skies, which inhibit precipitation.
These arid regions are often far from moisture-bearing winds and are most developed on the western sides of continents, where the subtropical anticyclone is most intense. Examples include the Sahara, Atacama, Kalahari, and Sonoran deserts. An exception is the Horn of Africa, where dryness is due to the landmass orientation relative to atmospheric circulation.
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What is the typical weather like in tropical and subtropical deserts?
Tropical and subtropical deserts, found between 15° and 30° latitude, are dominated by subtropical anticyclones, resulting in descending air, clear skies, and limited precipitation. These deserts typically receive between 0 and 25 cm (0-10 inches) of rainfall annually, with rainfall being highly unreliable. Temperatures are high, with monthly averages ranging from 21 to 32 °C (70-90 °F), and daily temperature variations can be extreme. The highest air temperatures on Earth have been recorded in these regions, such as in Death Valley and Libya. Some West Coast deserts experience cooler temperatures (monthly means of 15–21 °C [59–70 °F]) due to cold ocean currents, often accompanied by fog and low clouds.
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Why do tropical and subtropical deserts receive so little rainfall?
Tropical and subtropical deserts get little rainfall because of their location within the Hadley cell circulation pattern. This pattern brings dry air to these regions, inhibiting precipitation.
Near the Equator, air rises, cools, and releases moisture as rain. This air then moves poleward, descends in the subtropics (between 15° and 30° latitude), and becomes compressed and warmer, further reducing its ability to form clouds and rain. Additionally, many deserts are located far from the coast or on the western sides of continents, where the effects of the subtropical anticyclone are most intense. The result is a consistently dry environment with minimal rainfall.
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How do plants and animals adapt to life in these desert climates?
In tropical and subtropical deserts, plants and animals have developed unique strategies to survive the harsh conditions.
Plant Adaptations
* Xerophytes Most desert plants are xerophytes, which are adapted for arid conditions. Some are phreatophytes and rely on groundwater by using deep roots.
* Succulents Succulents, such as cacti and agaves, have thick, fleshy tissues for water storage. Some have small leaves or no leaves to minimize water loss.
* Stomata Many succulents have stomata that open at night to take in carbon dioxide and minimize water loss during the day.
* Dormancy Perennial plants may become inactive during dry periods or use underground organs like bulbs and rhizomes to survive until rain triggers growth.
* Ephemerals Ephemeral plants survive as dormant seeds, germinating rapidly after rain to quickly flower and reproduce before the soil dries out.Animal Adaptations
- Nocturnal Behavior Many desert animals avoid the heat of the day by staying underground in burrows and emerging only at night to feed.
- Water Conservation Desert animals have specialized skin that is relatively impervious to water. Some animals cool exhaled air to condense and reabsorb water in the nasal passages.
- Dormancy Some animals, like snails, can remain dormant for extended periods during dry conditions. Reproduction may also cease in extreme drought years for some animals, such as lizards.
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What are some well-known examples of tropical and subtropical deserts around the world?
Tropical and subtropical desert climates are influenced by subtropical anticyclones, resulting in descending air, clear skies, and minimal precipitation. These deserts, typically found between 15° and 30° latitude, have extreme temperature variations and average monthly temperatures between 21–32 °C (70–90 °F).
Well-known examples include:
* Sahara Desert Spanning much of North Africa, it features both dry subtropical and tropical climates.
* Arabian Desert Located in Southwest Asia, much of it lies north of the Tropic of Cancer, and experiences intense summer heat and low rainfall.
* Atacama Desert Situated along the Pacific coast of South America in northern Chile, it's one of the driest regions globally, with unique cool temperatures due to the Peru Current.7 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
Tropical and subtropical desert climate, major climate type of the Köppen classification dominated in all months by the subtropical anticyclone (or subtropical high), with its descending air, elevated inversions, and clear skies. Such an atmospheric environment inhibits precipitation. Most of Earth’s tropical, true desert (BW) climates occur between 15° and 30° latitude, at the poleward end of the Hadley cell circulation (see atmosphere). In the Köppen-Geiger-Pohl system, this climate is divided between the tropical desert (BWh) and subtropical desert (part of BWk) subtypes.
The most extreme arid areas also are far removed from sources of moisture-bearing winds in the interiors of continents and are best developed on the western sides of continents, where the subtropical anticyclone shows its most intense development. An exception to the general tendency for aridity to be associated with subsidence is in the so-called Horn of Africa region, where the dryness of Somalia is caused more by the orientation of the landmass in relation to the atmospheric circulation. Both the high- and low-sun monsoonal winds blow parallel to the coast, so that moisture-laden maritime air can penetrate over land only infrequently.
In most low-latitude deserts, cloud cover is uncommon (fewer than 30 days per year have clouds in some areas). Precipitation amounts are mostly in the range 0–25 cm (0–10 inches), although the unreliability of precipitation is more significant than the small totals. Average figures have little meaning; a location with a 10-year mean of 5 cm (2 inches), for example, might have received 50 cm (about 20 inches) in one year as a result of an unusual intrusion of moist air, followed by nine years with no measurable precipitation.
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Temperatures are high, with monthly means in the range 21–32 °C (70–90 °F). Daily temperature variations are extreme. Ranges of 35 °C (63 °F) are not unknown when daytime maxima in excess of 40 °C (104 °F) are followed by a rapid nocturnal temperature drop brought about by the limited capacity of the dry, cloudless desert air to emit infrared radiation to the ground to offset radiation loss from the surface at night. The highest air temperatures recorded on Earth have been in the BWh regions; for example, in shaded, well-ventilated locations, Death Valley in the western United States has reached 57 °C (135 °F), while al-ʿAzīzīyah in Libya has had a recorded high of 58 °C (136 °F). Actual surface temperatures may reach 82 °C (180 °F) on dry sand under intense sunshine.
An interesting variant of tropical and subtropical deserts are the so-called West Coast Desert areas found on the western coastal margins of the regions discussed above (such as in the Sonoran Desert of North America, the Peru and Atacama deserts of South America, and the Sahara [Moroccan part] and Namib deserts of Africa). These areas are much cooler than their latitude would suggest (monthly mean temperatures of only 15–21 °C [59–70 °F]), and parts are classified as BWk in Köppen’s scheme. The cooling results from airflow off adjacent coastal waters where upwelling of the ocean gives rise to cold currents. Deserts of this sort are subject to frequent fog and low-level clouds; yet they are extremely arid. Some parts of the Atacama Desert, for example, have recorded no precipitation for 20 years.