White Sands National Monument, New Mexico, USA Wadi Dhar, Yemen Dead Vleii, Namib Desert DESERT...
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Transcript of White Sands National Monument, New Mexico, USA Wadi Dhar, Yemen Dead Vleii, Namib Desert DESERT...
White Sands National Monument, New Mexico, USA
Wadi Dhar, Yemen
Dead Vleii, Namib DesertDESERTINTRODUCTION
Describe the characteristics and distribution of the two ecosystems listed in the syllabus (tropical rainforest and tropical desert).• Explain the relationship in each ecosystem of natural vegetation, wildlife and climate.
DISTRIBUTION OF DESERTS
Annual precipitation in deserts is less than 250mm and less than 100mm in extreme deserts. Deserts have large diurnal temperature ranges.
Deserts are located near the tropics (Tropic of Cancer and the Tropic of Capricorn). Some of the world's most famous deserts include:
Sahara in Northern AfricaKalahari in Southern AfricaAtacama in South AmericaGobi in Central AsiaArabian in the Middle EastGreat Victoria and Great Sandy in
AustraliaMojave and Chihuahuan of North
America
Antarctica is sometimes classified as a desert because it actually has very low levels of precipitation. However, when we talk about deserts in this section of the desert we mean sandy deserts.
Types of Deserts
Desert Types There are 5 main types of deserts
1.Subtropical Deserts – 30o n/s
2.Rain shadow deserts on Leeward side of major Mountain ranges
3.Continental Interior Deserts- center of continents far from ocean 35-50 N
4.Coastal desert- prevailing onshore wind cooled by cold ocean current
5. Polar deserts- extremely cold and dry
How is a Hadley Cell Formed?
Sun heats
equator
Ground heats
air
Air rises and
cools in the
atmosphere
As air cools it can no longer
rise
Cold air sinks at
the Horse
Latitudes
WIND moves between high
and low pressure LOWHIGH
The trade winds in two belts on the equatorial sides of the Horse Latitudes heat up as they move toward the Equator. These dry winds dissipate cloud cover, allowing more sunlight to heat the land. Most of the major deserts of the world lie in areas crossed by the trade winds. The world's largest desert, the Sahara of North Africa, which has experienced temperatures as high as 57° C, is a trade wind desert.
Orographic deserts - deserts that receive little moisture due to the "rain shadow" effect of nearby mountains, e.g., Basin and Range of
Nevada and eastern Oregon's deserts.
Rain shadow deserts are formed because tall mountain ranges prevent moisture-rich clouds from reaching areas on the lee, or protected side, of the range. As air rises over the mountain, water is precipitated and the air loses its moisture content. A desert is formed in the leeside "shadow" of the range.
Latitude: -45 / Longitude: -73
Image showing the impact of the Andes Mountains on rainfall and vegetation. At left is southermost Chile, which appears quite lush, while Argentina (Patagonia) appears dry and brown. Bright turquoise lakes are the result of extremely fine sediment ground up by mountain glaciers and deposited in the lakes.
The rainshadow effect S.America
Pacific oceanAtlanticAtacama DesertPatagonian DesertThe AndesS-E trade windsNorth Westerlies
Midlatitude deserts
These deserts are in interior drainage far from oceans and have a wide range of annual temperatures.
Coastal deserts where cold oceans lie next to hot coastal regions - most of the precipitation falls over the oceans before it gets to the land, e.g., Atacama and Kalahari deserts.
Deserts are extremely dry (arid) places. True deserts normally have less than 250mm a year, although some deserts like the Atacama to the right can go years without any water. Deserts are very dry because the air that descends over them is very dry.
The air is dry because most of the moisture has fallen as precipitation over the Equator (tropical rainforests) before being pushed out and falling near the tropics. The air is also very dry because the air travelling from the equator to the tropics travels over land and not the sea.
This means that no additional moisture is picked up. Because there is no moisture in the air, there are very few clouds in deserts which means desert areas are exposed to high levels of incoming radiation from the sun. This means that daytime temperatures in the desert are very high.
However, the lack of cloud cover also means that a lot of outgoing radiation is able to escape, making desert temperatures very cold at night. So even though the annual temperature range in deserts is very low, the daily temperature range is very high. The daily temperature range is known as the diurnal temperature range.
Basins of inland drainage called playas or shotts
Dry ravines or wadis or arroyos
Alluvial fans can join together to form a bajada
This xerophytic or drought resistant vegetation has adapted to living in dry conditions by having small, twisted leaves with stomata which only open at night to allow respiration.
Perennials, such as ocotillo, become dormant between the rains. Once all moisture has evaporated from the soil, the plant drops its leaves and temporarily stops growing.
Instead of thorns, the creosote bush relies for protection on a smell and taste that wildlife find unpleasant. Creosote has an extensive double root system -- both radial and deep -- to accumulate water from both surface and ground water.
Cactus, xerophytic adaptations of the rose family, are among the most drought-resistant plants on the planet due to their absence of leaves, shallow root systems, ability to store water in their stems, spines for shade and waxy skin to seal in moisture.
Desert plants must act quickly when heat, moisture and light inform them it's time to bloom. Ephemerals are the sprinters of the plant world, sending flower stalks jetting out in a few days. The peak of this bloom may last for just days or many weeks, depending on the weather and difference in elevation.